SW! gm“! —

A MANUAL FOR THE CONSTRUCTION
OF LOW-COST ROADS IN PAKISTAN

Thais 501' the am d M. 3.
MfCHiGAN STATE COLLEGE

Taiammal Hussain Hashmi
194-8

 

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H495

A MANUAL FOR THE CONSTRUCTION OF
LOW-COST ROADS IN PAKISTAN

By
Tajammal Hussain Hashmi

 

A THESIS

Submitted to the School of Graduate Studies of Michigan
State College of Agriculture and Applied Science
in partial fulfillment of the requirements
' for the degree of
MASTER OF SCIENCE
Department of Civil Engineering
1948

EHESfig

"It is the minor roads that have been most neglected
in the past and will be in danger of further neglect if devel-
opment is too much from the trunks outwards. It is the minor
roads’that condition the whole business of rural marketing
and the material and social progress of the farmer. It is
by way of the minor roads that all schemes for rural uplift

and betterment will reach their target, or fail to do so."

Sir Kenneth Michell

206049

TABLE OF CONTENTS

ACKNOWLEDGEMENTS

INTRODUCTION

CHAPTER

I.
II.
III.
IV.
V.
VI.

VII.
VIII.

STABILIZED ROADS

SOIL STABILIZED ROADS

PORTLAND CEMENT STABILIZED ROADS

BITUMINOUS STABILIZATION

CHEMICALLY STABILIZED ROADS

UNTREATED SURFACES

Earth, Sand, Clay, Gravel and Stone
Roads

LOCATION AND DESIGN
CONCLUSIONS and RECOMMENDATIONS

SUGGESTED READING

Page

ll
18
53
84
106
150

163
177

186

ACKNOWLEDGENENTS

The author wishes to acknowledge the courtesies
extended by many individuals, Experiment Stations, En-
gineering Departments of Colleges, State Highway Depart-
ments, Engineering Journals, and Commercial firms in the
United States, too numerous to mention by name, in pro-

viding published material as well as advice.

The author is indebted to Professor C. L. Allen,
Head of the Department of Civil Engineering at Michigan
State College whose keen interest, constant encouragement,
mature judgement and kind advice has been invaluable in
this work. Thanks are also due to Professor G. C. Blom-
quiet for going through the manuscript critically and

helpful suggestions.

INTRODUCTION

Pakistan's first concern is to effectively utilize
all available resources, in order to build up an economy
worthy of the fifth largest nation in the world. Pakistan
has many assets, it is indeed richly endowed. Mighty
rivers flow down its rich and fertile valleys from snow
clad mountains, providing water for raising abundant crops
all the year round. The climate in most parts is vigorous
and bracing, fostering a rugged and sturdy population,
and conducive to the raising of file livestock and crops
of all types. Vast resources in hydro-electric power and
minerals await exploitation. The people are united in their
faith for Pakistan and millions have sacrificed their all
for the achievement of its independence. In Quid-i-Azem
Mbhd Ali Jinnah, the country has a leader who not only has
great vision and faith, but also possesses the tenacity
of purpose, experience and skill to bring our hapes and

aspirations to fruition.

In contrast to these assets, Pakistan has equally
formidable handicaps that need to be removed expeditiously.
There are such legacies of the past as a complete lack of
industries, extreme pressure on land resources and a low
level of income. The literacy level is low, public health
facilities are inadequate,and due to lack of technological
development, the vast wealth of the country in minerals,

 

 

III ill. 3.5: I

water-power and agriculture is inadequately exploited.
Last but not the least, roads which can be said to be a
country's measure of civilization, are woefully few and

poorly maintained.

This situation is clearly brought out by compar—
ing the road mileage per square mile area in Pakistan,

_with a recognized standardT given below:

Miles of Road per

 

 

Square mile of Area Type of Countryin U. S. A.
2.3 Highly developed industrial area
1.7 Highly developed agricultural area
1.4 Well deveIOped hilly area
0.7 Nbuntain area
0.3 Desert area

Pakistan has a road mileage of o.2e per square mile area
(Table I) and thus by this standard has less road mileage

than even a desert area in the United States.

The road mileage is compared with some other countries
in Table II. It will be seen that England has 900 per
cent and U. S. A., 500 per cent more roads than Pakistan.
In addition,while a vast majority of roads in other coun-
tries are metalled, 88 percent of Pakistan's roads are

'earth roads,indifferently constructed and maintained.

 

1"E. W. James, quoted by Kynnersley, T. R. S., in
Roadeor India. Padma Publications. 1946.

 

 

TABLE I
AN (excluding acceding states)

*RILEAGE or ROADS

 

MAINTAINED BI PUBLIC AUTHORITY IN PAKIST'

 

 

 

 

 

 

 

 

 

HIGH TYPE Low TYPE

MOdern L Total Road

Surfaces Nature Area Mileage

Bitumen Water Total Granular Soil Earth Unsur-Grand i? Sq' t9 Sq-

or Bound Metalled Material Fair Roads faced Total miles mile of
PROVINCE Cement Macadam Weather Total area
BENGAL 825 1650 2475 288 9000 7890 17178 19655 58080 0-34
PUNJAB 2540 290 3630 93 6670 6460 13223 15855 156060 0-26
N.N.F.P. 1159 119 1278 781 1307 332 2420 3698 14283 0'26
SIND 143 120 263 308 6480 4681 11469 11732 48136 0.24
BALUCHASTAN 523 38 561 1759 1044 1567 4350‘ 4911 54951 0'09
N.W.F.P. h 0
TRIBAL AREA 289 75 364 549 209 ——- 758 1122 84986 0-05
Total for
PAKISTAN 6279 2292 8571 3758 24710 20830 49398 57969 266476 0-23

*ndapted from the 1947 Indian Year Book. Times of India Press,, Bombay-
- t - . ,.
The figures for Bengal have been reduced to é th. and %/5 for PunJab, to compensate for the areas ceded to India.

 

   

 

 

 

‘ROAD MILEAGE IN VARIOUS COUNTRIES IN RELATION TO

Area in

TABLE N0. II

AREA AND POPULATION

ROad

Nhleage

Road Mile—
age per

t0 Square 100,000 of

 

lountry Square Miles Population Road Mileage Mile Populatioxa
United
Kingdom 88,748 45,601,000 178,904 2.02 392
France 212,741 42,010,000 392,147 1.84 934
U. s. 1. 2,973,776 122,775,046 3,068,921 1.03 2500
Germany 181,814 66,616,000 173,287 0.95 260
Italy 119,722 43,050,000 106,129 0.89 247
Pakistan 266,476 70,000,000 ' 57,969 0.22 83
(excluding
acceding
States)

 

*Kynnersley, T. R. S. 1946. Road for India.

tion Ltd. Bombay.

Padma Publica-

 

 

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It is, therefore, little wonder that our rural com-
munities are isolated, illiterate, and steeped in medieval-
ism. The technological scientific revolution which has
raised the plane of living in more progressive countries.
to an unprecedented level, has left our rural areas high

and dry.

Our educational, public health and agricultural
extension services have their headquarters in urban centres.
At present their effectiveness is severely curtailed as
the energy and enthusiasm of workers is sapped up by the
dust of communications. With a reasonably good system
of rural roads, mobile libraries, mobile public health
units, mobile livestock disease control units and mobile
agricultural services could be made available to rural
areas thereby multiplying the usefulness of existing equip-
ment and staff manifold. No agency can perform efficient
service if its staff is dissatisfied and discouraged. Good
workers who have ambition and intelligence do not wish to
work in the villages because of lack of elementary facili-
ties for their families and themselves. In the wake of
good roads alone will follow the development of health
services, the provision of educational facilities, the ex-

tension of technical information for improving agricul-

tural production, in fact the opening up of the villages

to the influence of progressive forces.

In spite of the very small size of the average
holding in the country (2-10 acres), the methods of farm- '
ing are extensive rather than intensive., This is so be-
cause the cultivation Of vegetables and fruits and the ex-
pansion of poultry farming or dairying are contingent upon
adequate transport facilities so that such perishable com-
modities could be assembled, processed and marketed without
delay and in good condition. An indirect result is the
severe shortage of food of high biological value in the
dietary of the peOple. This is true not only of Eastern
Pakistan where the deficiency has been more marked but al-
so of Western Pakistan. I"A recent (1939-40) survey in the
Lyallpur district - admittedly the best area in the country -

has revealed a marked deficiency in protective foods.

Facilities for gainful disposal of agricultural pro-
duce is fundamental totthe prosperity of the farmers. The
development of cOOperative which is a basic need in small
scale farming, and is almost non-existent in Pakistan, de-
pends on the availability of good roads so that collection
and assembling of produce from over a large area is made

possible to obtain the necessary volume for effective busi-

 

1"Report on an enquiry into Diets, States of Nutri-
tion and factors associated therewith, in relation to health
in the Lyallpur district. Punjab Public Health Dept.

 

.U U I Ill '1'] I'll! l U

ness Operations.

Yet another advantage of a sound road system is the
prompt transport of peOples and commodities during unfor-
seen national emergencies. Military and defense needs
require efficient communication for both the movement of
men and supplies. NO modern state can afford to neglect

its communications.

There are many more arguments that are equally con-
vincing and are generally recognized in principal. Rarely,
however, is any attention given to these when considering
a specific project. The sanctioning authorities usually
demand a favorable balance of cost to earnings and while
it is easy for a hydroelectric scheme or an irrigation
project to prove its worth in annes and pies, it is diffi-
cult in the case of a road project. In a project like the
making of a rural road, the intangible and the indirect
benefits so outweigh the tangible ones that it would be
unfair to consider its merits from that standpoint. A
road is as much an educational institution as it is a busi—
ness venture and should be so treated, particularly in

under developed sections.
DEVELOPMENT PLANS

Road develOpment has always lagged behind the needs
of the country. Except for the large trunk roads which

have been well maintained due to military exPediency, roads,

particularly in rural areas have been very inadequate.

In 1927, a special road committee appointed by the late
government of India was instrumental in creating consider-
able interest in the development of roads. National planning
which included all fields of endeavour, was taken up very
enthusiastically towards the termination of the last war.

A road plan for post-war development was one Of the series
of departmental plans. The chief Engineers of all pro-
vinces met in a conference at Nagpur, India, in 1943 and
considered igtgr'alia, road develOpment policies and deter-
mined post-war needs for roads. Their recommendations

have been the basis Of plans for the various provinces.

The authors Of the I"Bombay plan, the premier un-official
plan, envisaged a doubling of the road mileage in the coun-
try over a 20 years period. This plan envisaged the link-
ing of all villages with a population of 1000 and more,
with the main highways, such that no village of that size
should be more than half a mile from a highway. Pakistan
will, no doubt, consider road develOpment in its territories
as soon as conditions permit and it can be anticipated that
at least a doubling of the present road mileage will be
determined as the largest for the immediate future. On

a twenty years basis it would be advisable to aim at one

!

 

O

0 Sir P. Thekurdas. 1944 A Brief Memorandum Outlining
a Plan of Eeonomie Development for India. Penquin

Books, New York.

mile of road per square mile area and would mean a 3.5
fold increase in existing road mileage. Even this is con-
siderably lower than our needs. According to the standard
mentioned before, James (10c. cit.), if we aim to be in
the category of a 'highly developed agricultural area'

we will need a six fold increase in our road mileage.
TYPE OF ROADS

A large part of the new road mileage will he village

roads. Such roads should be able to give reasonable ser-

vice as arteries of trade and be able to bear transport

of agricultural produce from the rural areas to the markets.
The Bombay plan envisages the modernizing of all earth
roads. In Pakistan it will not be possible to build a
large mileage of metalled roads in the immediate future.

The choice is not restricted, however, to expensive high-
ways and no roads. The available funds can be utilized ’
very effectively by building low cost roads in the initial
stages. Such roads can be quickly built by utilizing mater-
ials ready at hand. The expansion will come in the form

of less expensive but improved type of roads. A great deal
of experience in methods of constructing such roads has ac-
cumulated from work in the United States of America and from
air-field construction in all operational theatres in the

last war. A variety of means has been.succes$fu1ly employed

to stabilize the soil for road surfaces. Such soil stabilized

roads are now generally recognized‘ as being most suitable
for meeting the immediate requirements for inexpensive yet
serviceable roads. The favourable features Of these roads
include (1) low initial cost, (2) utilization of locally
available materials, (3) low maintenance costs, as stabilized
roads need less frequent dragging, blading and reworking,

and (4) greater safety and comfort, as with stabilized sur-

4 faces loose pebbles and dust are eliminated. Roads, however,
whether of the inexpensive or of the high cost type, involve
considerable labour and expense. It is, therefore, a very
costly process to neglect careful planning in the construc-
tion of low cost roads. All low cost roads should be so
built, that they can be converted into a higher type when-
ever funds permit or traffic conditions warrant. Not in-
frequently, where low cost roads have not been built with

an eye to future requirements, the 01d roads have to be

entirely scrapped when it is decided to modernize them.

Much of the work done on the location and construction
of soil stabiliyed roads is of recent origin and is dis-
persed in reports and bulletins 0f the various experimental
stations and State highway departments. The author has on-
deavoured to bring together this material in the form of a
handy manual which may serve as a practical guide in the con-

struction and maintenance of low cost roads.

 

*In 'A food_plan for India', with a forward by Pro-
fessor A. V. Hill. Royal Institute of International Affairs.
Oxford University Press, London. 1945.

11

CHAPTER I
STABILIZED ROADS

The stabilized road is one of the more recent.deve10p-
ments in highway construction. The difficulty in providing
satisfactory low cost roads for the enormous mileage in
rural areas has taxed the ingenuity of the highway engineer
for a number of years. Mechanical stabilization and the
use of portland cement, bituminous materials, chemicals,
industrial waste and numerous by-products are suggested
for use as admixtures to increase the resistance of soil
mixtures to deformation and wear. Such roads are primarily
designed to utilize available low-cost materials and provide

a serviceable highway.
PRINCIPLES OF STABILIZATION

Stabilization has been defined as a combination of
brider-soil and aggregate preferably Obtained at or near
the site of stabilization, manipulated and treated with or
without admixtures, and compacted so that it will remain
in its compacted state without detrimental change in shape
or volume under the force of traffic and heavy loads. The
methods employed include the use of admixtures, compaction
and densification by specific technical theory and labora-'
tory control. Optimum water control is fundamental with
gradation. Admixtures may be of soil materials, delinques-

cent chemicals, solution of electrolytes, soluble cementitions

chemicals, primes and neutralizers, and insoluble binders.
A broder definition that is frequently used states, "A
stabilized road is one that will not flow laterally under

a load."

Three factors are fundamental to stabilization;
gradation, water, and compaction or densification. All
three of these are also interdependent upon each other in
such a manner that they must be considered together. For
stability two types of resistance are needed; the one pro-
duced by the internal friction of the particles and the
other stickitiveness. This is effected by gradation. Each
of the components of a well-graded soil adds its own peculiar
characteristics to the stability of the whole. Clay due to
its cohesive properties when wet provides cohesion and acts
somewhat as a cement between the larger particles of silt
and sand which have no cohesive prOperties. Also, clay,
due to its mineral composition and crystalline structure
may be considered as the active ingredient, in the sense
that its properties can be changed somewhat by chemical
action. Silt provides pore filler and embedment for the
sand grains and contributes to the internal friction of
the whole. Sand and gravel, usually of less than 1 inch
maximum particle diameter, supply the greatest amount of
internal friction and affords a hard wearing course for the

' road.

lProctor discovered that compacted mixtures of such
materials possess an Optimum moisture content and maximum
density for each degree of compactive effort used in mould-
ing specimens. The moisture in the soil at maximum density
is called the optimum moisture content for this compactive
effort. ZHOgentogler state that all soil mixtures suitable
for road use are stable at some water contents, and water
in stable roads in more adhesive than free water and stability
depends upon the thickness of the absorbed moisture film,
and the principal aims of stabilization are to make the
soils as dense as possible and to prevent the thickness of

the moisture film from changing.

Use is made of these principles of stabilization in
working towards two objectives; the most stable combination
of the available materials, and as great a degree of per-
manence of that stability as is possible by means of me-
chanical consolidation and the use Of admixtures. To per-
form satisfactorily, such a mixture must neither dust, be;
come slippery when wet, nor ravel appreciably during dry

weather.

 

lProctor, R. R. Fundamental Principles of Soil Com-
paction. Engineering News Record, g, (9, 10). 1933.

‘ 2RegentOgler, C. A. and T. A. Kelley. 1937. Role
of Soil Binders and Aggregates in Soil Stabilization. Pro-
ceedings American Road Builders Association.

14

GENERAL PROCEDURE IN STABILIZATION

In the construction of a stabilized road, as in other
types, there is a general procedure which includes the pre-
liminary work and the actual construction. In this treat-
ment of the general procedure, the soil survey is given as

the first step in the preliminary investigation.

SOIL Profile: --— Soil surveys and the resulting soil profile
are as important on stabilized roads as on other types, and
are used for determining the characteristics of the sub-
grade and road metal and for locating sources of burrows.

In addition, particular use can be made of such survey in
mapping the road surfacr to show the amount and type of

the material already in the road. Soil surveys, in most
instances, can be expedited considerably by utilizing avail-
able geological and agricultural soil maps. The . soil
profile, as often used include the mapping and presentation
of data from a complete investigation of all soil and geologi-
cal stratification encountered in subgrade, in cut, or in
foundation, which may influence the design, construction

and maintenance of a highway. A complete profile is an un-
dertaking too comprehensive for an average stabilization

project.

Bornigs are taken as close to the centre line of
the prOposed road as possible, at interval ranging from 25

to 500 feet depending on soil conditions; and samples are

collected for laboratory classification. A record is made
of the surface elevation and of the depth, thickness, and
description of each soil layer encountered in the hole.

It is customary to map the layers to a depth of at least
four feet below the proposed subgrade. In the case of old
earth roads which are to be stabilized a performance sur-
vey of the such roads is also made. Any indications of in-
stability are carefully inspected, and apparent reasons for

other types of failures are noted.
MATERIALS USED FOR STABILIZATION

The materials used for stabilization are limitbd in
number although their applications are numerous. Soil, the
most common of engineering materials, is the principal ma-
terial of stabilization. Ranging from clay and silt through
fine sands, coarse sands, to the gravels, are the soil and
aggregate materials that provide the structure of the im-
proved base as well as the subgrade. These are combined
with portland cement, bitumin, clacium chloride, sodium
chloride and miscellaneous materials like molasses to give

a suitable mixture for stabilized roads.
TYPES OF STABILIZATION

The various types of stabilization are described as

under:---

MECHANICAL Stabilization: --- The combination of soil and

aggregate in optimum prOportions, suitably compacted, pro-
vides a relatively stable mixture for all weather roads.
The wet-weather Stability of sand and noncohesive particles
and the binding power of clay when dry give mechanically
stabilized mixtures their all—weather stability. However
the achievement of mechanical stabilization, under field
conditions is not alway practicable since ingredients are
often not available in the immediate vicinity of the road.
Under such conditions it becomes very expensive to trans-
port large quantities of sand, clay or other ingredients
from distant sources. It is then economical to use small
quantities of more expensive stabilizers such as bituminous

materials, portland cement etc.
(PORTLAND CEMENT STABILIZATION

The use of portland cement as andadmixture in stabili-
zation has been applied to a wide range of soil types.
A soil-cement combination produces a semi-rigid pavement
rather than the flexible type characteristic of other ad-
mixtures. The chemical reaction between cement and soil
appears to have the same function in a soil-cement mixture
as in an aggregate-cement mixture. 'The soil-cement mix-
ture may be considered as a semi-rigid slob having sufficient
strength to carry the load. Since these mixtures are com-
paratively weaker than cement concrete, special attention

should be given to the provision of an adequate subgrade.

l7

BITUIINOUS STABILIZATION

In the stabilization of relatively fine-grained soil
the use of bituminous admixtures produces in the soil ma-
terial a high degree of resistance to the deleterious effect
of water. The heavier grades of bituminous materials im-
part some degree of binder action to the soils, but the
principal benefit appears to be in making it impervious
to water. A wearing surface is sometimes applied to pro-

tect the base material from~the abrasive action of traffic.

CHEMICAL STABILIZATION

The use of chemical admixtures, such as calcium or
sodium chloride, with mechanically Stabilized mixtures has
gained great popularity in recent years. These admixtures
are normally used with soil-aggregate gradation having me-
chanical stability, where in they serve to increase the
density of the compacted mass and to minimize daily and

seasonal fluctuations in moisture content.

l8

CHAPTER II
I
SOIL STABILIZED ROADS

Soil stabilization is the process of giving natural
soil enough abrasive resistance and shear strength to ac-
commOdate traffic or loads under prevalent weather condi-

tions, without detrimental deformation.

COMPOSITION OF SOIL

The 8011 mass, regardless of individual characteristics
of composition and structure, is made up of the same group
of constituents, namely, (1) soil solids, (2) soil moisture,
and (5) soil air. Soil solids may be further divided into
mineral matter, derived from rock or parent soil material
by various weathering processes, and organic matter com-
posed of the residue of vegetation. Soil moisture is the
moisture contained in soils which originate as ground water,
capillary water, surface water or precipitation. Soil air
is entrapped air within the soil voids which occupies the
volume that is not taken up by the soil solids and soil

mixture, and thus complete the soil mass.

GRAIN size demensions and behaviour of soil solids: -~- All
soils are divided by size into three principal parts, namely,
sand, silt and clay sizes. In different soils the soil
properties may be derived from different sources, but the

particles which fall in the same size group will have cer-

tain similiar characteristics.

Fine sand group consists Of all particles pasting
No. 40 sieve and retained on No. 270 sieve (0.05 m.m.),and
these particles may be considered as inert in their phy-
sical reaction with water. Capillary gravitational water
may enter and fill the pores in the particles themselves,
ane all or part of the voids between the particles, but
there is no tendency for the individual particles to see

parate from one another.

(Silt, is meant all particles finer than No. 270
(0.05 m.m.) sieve and larger than 0.005 m. m. in diameter -
and these particles may likewise be considered as inert.
Their physical property when in contact with water are
much the same as for sand except that the individual grains,
and therefore the voids between the grains are much
smaller in size. This means that a column of silt can
usually take more water and lift it higher by capillary

action, than a corresponding column of sand.

All particles smaller than 0.005 m.m. in diameter
constitute the clay size, and all particles smaller than
0.001 m.m. in diameter are known as colloids. The clay
particles are the active constituents of a soil binder
mixture and most of the activity is furnished by colloids.
If a column of clay is exposed to capillary or gravitation

water, not only will the voids between the particles be

filled but each of the clay grain will tend to absorb a
film of water around itself and thereby separate from

its neighbour. This causes the total soil to a increase
in volume and become plastic with the addition of moisture
and to decrease in 8178 when the moisture is lost. A
clay grain that is a part of a soil mixture, however will
seldom be able to absorb the maximum thickness of water
film of which it is capable to, due to two reasons.

(1) Loss of moisture caused by evaporation frOm some con-
necting surface of the soil mass and, (2) confinement due
to internal compaction or external pressure. When the
absorbed film is much thinner than ordinary water, and
the clay grains become a strong binding medium instead

of a lubricant.

A good type of soil binder will contain enough sand
and silt grains to assure stability in the mass when wet
and enough clay grains to furnish cohesion to the mass
when damp or dry. If there are not enough active day
particles to coat the surface of the inert sand and silt
particles fairly well, the mixture will lack cohesion and
will be extremely difficult to set up in road construction.
If on the other hand there is an over abundance of active
clay particles in a soil mixture, these particles will
absorb enough water to slide on each other and thus at
as a lubricant instead of a binder between the sand and

soil particles and thus result in a base which is unstable

under traffic.
CLASSIFICATIONS 0F SOIL

The engineer selects samples of all of the soils
that differ in appearance and enough samples of similar
materials to establish their identity. The next problem
is to analize the soil samples to determine which of the
samples belong to the same strata. 1Soils are classified
into eight distinct types in accordance with their struc-
tural prOperties. The Public Roads Administration (U.S.A.)

has the following descriptions of these: --—

Soil type Apl. Excellent binder for soil roads, contain-
ing proper balance of coarse and fine materials, high
internal friction and cohesion. Absence of detrimental

shrinkage, expansion, capillarity or elasticity.

Soil type A—2. Contains either an excess of sand or an
excess of clay. May be stable in dry weather and soft
in wet weather or rough and dusty in dry weather and fair-

ly stable in wet weather.

Soil type A-S. Almost pure sand. Flows under wheel

loads but furnishes excellent supporting medium.

Soil type A94. Predominance of silt. Absence of cohesion.

 

1U. s. Bureauof Public Roads, Classification of Soils.
as quoted by Brown, V. J. (1936). Soil Stabilization after C. A.
Hogentogler. Gillete Publishing Co. Chicago.

Absorbs water so quickly as to disrupt structures. It is
subject to serious frost heaving, and may form stable road

when dry but will soften in wet weather.

Soil type A-5. Predominance of silt as tn A-4 but with
added elastic porperties even in dry state. Will not re-

tain compacted density.

Soil type A-6. Predominance of sticky, collodial clay.
Practically non elastic and can be compacted to high
pavement densities. Absorbs water slowly and has high

shrinkage, often interferes with macadam bond.

Soil type A-7. Predominance of clay but often elastic.
May have tremendous amounts. Volume changes and cause

concrete pavement to crack and fault.

Soil type A-B. Contains high amount of peak or muck.
Spongy level settle down under load. High capillarity
and elasticity.

SOIL USE

Until recently efforts in road construct on were
concentrated on obtaining a good surface without regard
to soil which composed the major part of the structure and
which constituted all of the foundation. This resulted
in placing poor soil in the structure where it would do
most harm, and good soil being placed in the structure

where it would do the Least good, the result being the

excessive maintenance cost, mat failure, warping and crack-
ing and costly reconstruction. The following are the aids
and information available to the engineer to improve the

construction.

1. Preliminary tests to determine the type of soil occurring
on each project.

2. A soil profile showing the extent of each type of soil.

5. A soil report containing recommendations for design
and reasons for disposition and treatment of soils.

4. A knowledge of the difference between good and poor
soil for specific projects.

5. Sample tests to help the field man to distinguish soil
type.

6. Soil selection and disposition of the soils encountered
on the project.

7. The method of soil improvement by addition of water,

rolling or other treatment are included.
PRELIMINARY SOIL SURVEY

The purpose of the soil survey is to (1) determine
the extent and characteristics of the various natural
soil foundations on and adjacent to the proposed alignment
which will affect the construction and durability of the
roadway; (2) to obtain samples of representative soils,
test their, and, from the results of tests, determine the

best use of the soils available, and the best method of

24

handling these soils during construction; and (5) to have
available, from construction records and the final soil
profile, a record of complete road which may be used in
road-life studies and as a basis for design when similar
soils and soil conditions are encountered on future pro-

Jects.

SOIL.Irofile: --- The soil profile is obtained by examin-

ing the soil in the natural field condition. The work

is best accomplished by examining excavations, road cuts,
etc. The method of using a soil auger is most common.

There is no definite procedure, the only consideration is

to examine the soil at close intervals to determine the

soil type nd by boring deep enough to penetrate the more

or less nonuniform layers of soil and soil material.
Particular attention should be paid to the following pro-
perties proceeding in a systematic way. (1) Texture. Suc-
cessive layers differing in texture or fineness or coarseness
shouhd be carefully examined up to 5 or 6 feet below the
proposed grade line. (2) Colour. Layers of different colours
should be described and their thickness given. (3)1§££ug-
3233. Structure is defined as the kind and size of particle
aggregation. Each layer that differs according to the
structure should be examined and note made of (a) fine
granular structure, (b) coarse granular structure, (c) layer-
ed or plately structure in which the material splits into
thin plates, (d) buckshot structures in which the soil on

25

\.

drying breaks up into angular fragments (containing more
clay or lime), and (e) single grain structure like flour

or sand. (4) Consistangy. Determination of the successive
layers differing in stickiness, friability and plastaty,
and its description should be given. (5) Compactness.

The degree of resistance to the penetration of a pointed
instrument is compactness. It should be determined for

the several layers. (6) Cementation. It should be de-
termined that the resistance to penetration is due to any
cementation and the probable cementing material should

be ascertained. (7). Chemical Composition. Although

the chemical composition of the various soils cannot be
determined in the field yet there are a number of features
that cankbscertained. Field tests can determine the pro;
sence of horizons with concentration of organic matter

or of salts of the alkalis and alkaline earth. Organic
matter inthe surface soil is recognised by its dark colour
and the relative intensity of dark colour gives the per-

eentage.
SOIL TESTING

After ascertaining the characteristics described
above, samples of soil are sent to the laboratory for de-
termining the (1) amount of soil fines, (2) amount of coarse
aggregates, and (3) moisture content necessary for compac-

tion. Five pounds sample of soil from each layer is ob-

tained with pick and shovel from the test pit dug at loca-

tions by the borings. Each sample is placed in a canvas»
‘bag, tied securely, marked with proper identification and
sent to laboratory. A sufficient number of samples must
be taken to determine the range in test results for what

appears to be the same layer.

MECHANICAL ANALYSIS

Samples of soil received in the laboratory are
spread out in large shallow pans and allowed to dry with-
out the direct application of heat. After they become so
dry that dust would form when the lumps were rubbed with
the fingers they are pulverized in a large porcelain mor-
tar by a rubber covered pestle from these large samples,
approximately one of the following amounts depending upon
the amount of gravelly material are quartered out: ---

If largely silt and clay --- 65 grams
If of sandy texture ---115 grams

If containing gravel at
least ---500 grams

The rest of the sample is passed through No. 40 sieve and
the coarse material discarded. At least 500 grams of the

finer material would be placed in a container and set aside

for the moisture equivalent test.

A soil material may be sub-divided into fractions
according to the si7e of the constituents particles. Such
a division is known as 'Mechanical analysis of soil'. In

a mechanical analysis coarser fractions are separated by
use of sieve; finer particles are separated by method of
wet analysis based principally on the speed of sedimenta-
tion. The finer the particles, the more time it requires

to settle through a contain distance.
HYDROMETER.METHOD

It is the methed of wet analysis originally prepared
in 1926 by Professor Bonyoneos of Michigan State College.
This method depends upon variation in the density of a
soil suspension contained in a one liter graduated cylinder.
The density of the suspension is measured with the hydro-
meter at determined time intervals, than the coarse dia-
meter of particles in suspension at a given time and the
percentage of particles finer than that coarsest (suspended)
diameter are computed. The computations are based on Stokes

Formula: --- v . .2. 31:2 s - so
5 n

Speed of sinking Cm. Per. Sec.
Acceleration of gravity Cm/secz

Radius of particles. Cm.

m HQ '4
'0

Density of particles g/sec.
SO8 Density of the liquid g/sec.

n 8 Co-efficient of viscosity of the liquid,
(poises ie.gm/cm./sec).

CENTRIFUGE MOISTURE EQUIVALENT

A liquid strongly attached to the walls of a tube

resists the action of a pressure applied along the axis
of the tube. Should the pressure exceed a certain limit,
the liquid will be removed from the tube wholly or partly;
it is shorn off from the walls. In a similar manner, mois-
ture in a soil pore attached by the soil particles can
be removed if additional pressure is applied. The amount
of moisture that can be removed depends on the intensity
of molecular attractive force and on the value of pressure.
To capacity of a soil to hold water under the action of
a force which tend to remove it is termed 'water holding
capacity'. The moisture equivalent is the moisture con-
tent of the soil which initially saturated, has been cen-

trifuged for a given time with a given centrifugal acceler-
- ation. Host of the water held in most coarser interstices
of a soil is removed, while all the moisture in finer in-
tersitices may remain.. The value of moisture equivalent
for very permeable soil is Sfiator less. Sandy loam and
other fairly permeable soils generally have a moisture
equivalent 5-12. The moisture equivalent of clay may
be 40, 50 or more. Soils possessing a low moisture equiva-

lent dryout easily and vice versa.
SIEVE ANALYSIS

A portion of the sample is allowed to dry in an

29

oven at approximately 110 degree C. overnight. It is
then weighed and passed through a nest of sievesof dif-
ferent sizes. The material remaining in each sieve after
thorough shaking and that passing the No. 200 is weighed

on a suitable balance.

 

 

 

 

Sieve size Wt. in grams Percentage Cumulative
retained retained percent passing
1 inch O '0 100
i inch 10 2 98
5/8 inch 80 16 82
No. 4 85 17 65
No. 10 75 15 ' 50
lo. 40 95 19 31
No. 270’ 70 14 17
Passing 270 85 17 --

Total grams = 500
’(H0. 200 mesh sieve often substituted)

A study of the table will show that the cumulative percents
reported as passing, for example, No. 4 sieve is 65 per—
cent of the 500 grams samples went through No. 4 sieve.
Incidently, this gradation will make a good stabilization
mixture. Sometimes it is essential to wash the portion

of the sample retained on No. 200 sieve through that sieve.

The amount passing is computed.

.30

LIQUID LIMIT

This is the percentage of moisture at which the soil
changes from a plastic to a liquid condition. It is
liquid when it begins to flow under certain arbitrary con-
ditions as explained below. Apparatus required. Liquid
limit device with grooving tool, 25 m. m. graduated burette
with stand; spatula, distilled water.

PROcedure: --— 50 gms of the soil are placed in a brass
dish and thoroughly mixed with water (added for convenience
through the burette) to a stiff but workable state. The
surface is smoothed off in a half-moon in the front of

the dish and a groove cut with a special tool. The cup

is pinned in a machine and the crank is turned. The num-
ber 4 shocks required to Just close the groove cut in

the sample is recorded in the moisture contents determined
by over drying as small sample. The soil is again wetted
and the entire procedure repeated until there are several
values ranging 25 shocks. The data are their made and

plotted in the form of a curve and the mean value taken.
PLASTIC LIMIT

Plastic limit is the percentage moisture at which
the soil changes from a solid to a plastic condition. Usual-
ly some of the soil remaining from the liquid limit test
is mixed with some dry soil until it is Just slightly

31

workable. It is then rolled with the palm of the hand
over the glass plates in the threads 1/8 inch in diameter
until these threads Just begin to crumble. The moisture

content is then determined by overdrying a small sample.
PLASTICITY INDEX

The numerical difference between the liquid limit
and the plastic limit is defined as the 'plasticity index'.

SHRINKAGE TEST

Apparatus: --- Glass cup with ground glass edge,
glass plate with three prongs, milk dish, steel straight
edge, 25 c.c. glass graduate, mercury, porcelain mixing

dish, spatula, distilled water.

Procedure: --- The soil is mixed with water to

slightly abdve the liquid limit. It is their placed in

a mill dish in three layers and after each addition it

is carefully tapered to remove the air bubbles. The soil
is then scraped off level to the top of the dish with the
straight edge and the samples weighed. It is first air
dried and then oven dried to constant weight. After cool-
ing in a desicator the dry weight in sustained. The mois-
ture content is computed. The volume of the pat is deter-
mined by filling the glass cup with mercury, immersing

the specimen and measuring the overflow in the 25 c.c.‘

graduated cylinder. The shrinkage limit and shrinkage

32

ratio are computed as follows.

Shrinkage limit Mbisture Content Percent -

100 x VOlume of dish - Vol of drysodl
Wt. of dry soil

Wei ht of dr soil
Volume of dry soII

THE LINEAR SHRINKAGE TEST

Shrinkage Ratio

The test as made by the Texas Highway Department,
is the loss in length expressed as a percentage of the 1
original wet length, incurred by a specimen in shrinkage
from the liquid limit state down to dryness.

A % by % by 5 inch bar specimen in formed in a
metal mould and the actual loss in length measured by
means of a rule, with 1/20 of an inch representing per

cent linear shrinkage.
DESIGN OF STABILIZED MIXTURES

There are two approaches to the preparation of stabi-
lized soil mixtures. (l) Graded mix for light traffic
build with best local materials available. The main pur—
pose of this road is to provide an inexpensive all-weather
surface for light traffic on rural roads. This surface
may become muddy or dusty and portions may get roughuor

smooth. The surface requires continual maintenance. This

type is described later in chapter 6 (2) Grades mix for
medium traffic constructed with a designed and proportioned
mix. This type provides adequate service for heavier
traffic than type No. 1 because the surface is wider and
thicker,the mixture is designed carefully and the various
steps in construction are controlled so as to produce a

dense mix. The steps are described below in detail.

The design of a soil mixture is based on, (1) the
grading of the combined coarse aggregates and soil mortar
as determined by mechanical analysis, and (2) the binder
properties of the fixes as disclosed by the plasticity
index test performed on the fraction of the soil pasSing
the No. 40 sieve. Materials falling within the following

gradations, by weights should produce good results.

Sieve Number 1" %" No. 4 No. 1O No. 60 No. 270
Percentage Passing 100 85-100 55-85 40-65 25-50 10-25

Materials larger than 1 inch can be used under certain con-
ditions but the amount should not exceed 10 per cent. The
maximum size should never exceed 1/5 of the thickness of
stabilized layer. The fraction passing the No. 270 sieve
should be less than 2/5 of the fraction passing the No. 40
sieve. Generally plasticity index of about 5 or less in-
dicates sufficient binder cohesion for roads to be construct-
ed on locations subjected to usually wet conditions, an

index of 4 to 8 for conditions of average moisture, and of

9 to 15 inclusive, only for the drier or the arid conditions.
Plasticity index exceeding 15 indicates that the soil is

not suitable for this type of construction.

The presence of undesirable organic substances is
indicated by liquid limits greater than those indicated
by the expression L.L : 1.6 x P.I - 14. The more
the liquid limit exceeds those values, the more unsatisfactory
the soil binder is apt to be, due to detrimental sponginess
and capillarity. Elimination of such properties in detri-
mental amount from the final road mixture may be accomp-
lished by keeping the liquid limits from exceeding about

35.
DESIGN OF MIXTURE

In designing a prOportionEd mix it is desirable
that limestone or slag screenings or pit run gravel be
incorporated in the mix. Stabilized mixtures might be
said to have three requirements according to the Indiana
State Highway Commissionz (Smith 1941).
(1) A well grades aggregate. This may be pit run gravel
provided it is well graded, crusher run limestone or slag
with a maximum size of 1% inch or as desired, _(2) A fine
aggregate such as stone or slag dust or sand, used to fill
the large voids in the coarse stone, and containing sufficient

material of minus 40 mesh size to give control of the plasticity

of the finished mix, and ——-

 

28mith, A. R. quoted by Brown, V. J. (1956). Soil
Stabilization after C. A. Hogentogler. Gilett Publication,
Chicago.

55

(5) A binder having a plasticity index of between 12-25.
When using an aggregate deficimmt in lime-rock particles,
a binder having a pH of less than 7 is not recommended.
Acid soils binder can be used, however, if the mixture
includes sufficient lime or limestone dust to neutralize

the soil.

A careful screen analysis should be made of each
magerial proposed for use in the stabilization and the
plasticity of each should be determined. It is often the
case that only one particular type or grading of fine ag-
gregate or clay may be obtained. The others must then be
selected so as to work satisfactorily with the constituents
which is available. It is necessary that physical tests
of the final mix show low capillarity, or water absorbing
properties, otherwise, the clay binder will act as a
lubricant during wet period. The soil fines of the finish-
ed mix (materials smaller than No. 40 mesh) should have a
liquid limit under 25, a plasticity index of 9 or less
and a centrifuge moisture equivalent under 20, for average

climatic conditions.

A convenient method for the design of stabilized
mixtures, suggested by the Kansas State Highway Commission
(Worley 1940)! is given below with an example to illustrate

its working.

 

aWorley, H. E. (1940) Design of Soil Mixtures for
Stabilized Road Surfaces. Roads and Street, g5, (5): 70.

56

A mix may be designed to meet gradation specification
very readily by means of rectangular graph method. The
percentage retained on No. 10 sieve may be plotted as or-
dinate and the percentage passing No. 200 sieve as abscissa.
Each material and the specification limit or limits within
which the mix is desired may be drawn on graph. The speci-

fications for this sample areas follows.

Sieve Number 1" %" N0. 4 No. 10 No. 40 No. 200

Percentage
Retained 0 0-25 40-60 50-70 65-80 80-92

The test results of the materials are given in the following
table. I

Percentagngetained 22 Sieves. Table I

No.
1' g" 3/8' 4 10 20 40 60 100 200 .02 .001 .1

Aggregates - _
No. l 0 25 54 76 90 92 94 95 96 97 100 .100 o
No. 2 0 24 6O 77 so 92 97 99 1
No. 3 0 3 11 18 so 54 90 9s 2
Binder Soil 0 1 l 2 4 4s 94 9

THREE material Mix: --- Three materials usually may be combined

to form a satisfactory mix. Using the materials in table x
plot aggregate No. l at A (90 percent passing No. 10 sieve
and 5 percent retained on No. 200). Then plot aggregate
No. 2 at B and binder soil at C. Draw line AB. Any point
on this line represents a combination of aggregate N0. 1

and aggregate N0. 2. Select a point E with in the specifica-

     

 

 

 

 

100 '
ffiree Magi/08 MM.

3' .90 w A (90,5)
S. 80 1 Panda? From 5/1980 atom”
§ To Feb/wed Iva/0 i - 60

60 £(60./4) POSS/71 II 200 - , 2'
E 9 {/oo sags/‘4
§ do
0)
Q< 40‘
S“ .30 \\
m,
e
+; 20 \
E:
S 10
R }B( ,8) do. 96)

O - A a a

20 .20 50 40 O?) 60 7'0 (90 30 (00

Percentage 106255019 N0. 200_

90 A Four Mflrff/flé MIX

  
      

C‘ (Ema/er)

 

£0.46)

A J_

fierce/72396 fle/émea' on Na 10

10 .20 .30 1'0 6'0 60 70 60 .90 100

Percen/‘éje Pass/”.9 N0 200

37

tions and draw a line from C through E to where it inter-
sects the line AB. Mark this intersection at D. The ratio

DE to DC gives the percentage of C in the mix.

Note: --- Ratio of distances are taken from projec-

tion of lines either on abseissa or ordinate.

DE 10 11 percent of binder soil.

Sg-z I
This leaves (lOO-ll) . 89 percent of(A + B)

AD _ 25 . 25.6 percent of (A + B) in B.

25.6% x 89% . 25% B or Aggregate No. 2
100 - 25.6 g 74.4% of (A + B) is A
74.4 x 89 = 66% A or Agg. No. 1.
The mix is then:
Agg. No. 1 66 percent
Agg. N0. 2 25 percent
Binder Soil _ll_percent
Total 100
The gradation may be calculated by taking 66 percent of
the percentage retained on each sieve of aggregate N0. 1
as given in table x, 25 percent of aggregate N0. 2, 11
percent of the percentage retained on each sieve of binder
soil, and taking the total of the percentage retained on

each sieve.

38

Table Y. Percentage Retained gn_Sieves.
- Ne. m.m. m.m.
Sieve No. 1" fi" 5/8” -4 10 20 4O 60 100 200 0.02 0.001.

Percentage
of Materials

66$ Agg. NO. l 0 16 36 .50 59 61 62 63 63 64 .66 66

25’ Agg. No. 2 O 6 14 18 20 21 22 25
11$ Binder Soil 0 0 5 10

Gradatlon of Mix 0 16 36 50 59 67 76 81 83 85 93 99

This gives us the gradation.
The plasticity index may be calculated as follows.

 

 

 

Table 2
Materials Proportion Percentage of P.I.
of Material material passing P.I. of ofmix
Used . N0. 40 sieve (A x B) Materials (CxD)(total
E-C)
Iw B '—_C'——'___EF—__"—1T—"TF_'
Agg. No. 1 66$ 6 4.0 6 24
A35. No. 2 23¢ 40 9.2 l 9
Binder Soil 11% 90 10.9 9 98

 

Total - 10096 25.1 1W

39

FOUR Material Mix: --- Sometimes a satisfactory mix can.

not be made from any three materials located, and four ma-
terials are required. The rectangular co-ordinate graph

can be used for designing a mix with any number of materials
although the process become more and more complicated and

more trials may be necessary as more materials are used.

Draw the line BF and select point G. This may be
selected anywhere on line BF. Draw the Line AG. Select
the point E within the specifications and draw line CE
cutting AG at D. The ratio of DE to DC gives the percentage
of C in the mix.

DE ; 6 u» 7% C or binder soil
DC 6'3"

This leaves 10096 - 796 a 9396 (A + B + F)

no : 64 g 7lfiof(A+B+F)isA.
IF. 9‘0

70$ x 95¢

66$ A or Agg. No. 1

Int; . $3 .. 29$of(A+B+F)is(B4-F)

29’ x 93$ 27% (B + F)

so :- 12 . 51.6! (13+r) is F.
E! 5'6

51.6’ x 27$ 3 9% F or Agg. No. 5.

100$ - 51.6% . 68.4fi of (B + F) is B.

68.4fi x 27$ 3 18% B or Aggregate_No. 2.
The mix is then: ---

Agg. No. l 66 percent

40

Agg. No. 2 18 percent

Agg. No. 5 9 percent

Binder Soil __Z_percent
Total 100

The gradation of the P.I. may be calculated as follows.
Table R

Percentage Percentage of Sieve
of material m.m m.m
1" %" 5/8" 4 10 20 4O 60 100 200 0.02 0.001.

66; Agg. No. l 0 16 56 50 59 61 62 65 65 64 66 66

18’ Agg. N0. 2 4 11 14 15 l7 17 18
9f Agg. No. 5 1 2 5 5 8 9
7’ Binder Soil 5 2

 

Gradation of Mix 0 16 36 50 59 65 74 79 81 86 90 100

Plasticity Index may be calculated as follows: ---

 

 

 

Table 3
Percentage P.I .
Materials Pr0p0rtion of of materials P.I. of of
materials used passing N0. 40 (AxB) material (CID) totxnl
._ 12-3)
A B C D E F
Agg. No. 1 66$ 6 4.0 6 24
Agg. No. 2 18¢ 40 7.2 l 7
Agg. No. 5 9% 89 8.0, 2 l6
Binder Soil 7’ 90 6.9 9 62 y‘_
Total 100$ ' 26.1 109 4

If the gradation of P.I. is not satisfactory another trial may
be made by shifting point C on line BF.

41

CONSTRUCTION

A stable surface should have sufficient shrearing
strength to carry the load imposed by traffic under condi-
tions of subgrade, climate and protection to which it will
be subjected without detrimental deformation or lateral
flow.

MATERIALS

Attempt should be made to use readily available
local materials which will provide an economical surface.
The type of materials available may differ widely in various
parts. Pr0per1y grades materials include sand, gravel,
crush or run or recombined crushed limestone, clay gravels,
limestone screenings, and sand of various gradings, to be
combined with binder to produced a desired grading and
Plasticity Index. An aggregate binder course depends for
its shearing strength upon two factors, (1) internal fric-
tion; and (2) cohesion. The interlocking action of the
aggregate particles furnishes the internal friction, the
fine sand and silt act as filter and provide capillary
bond. The binder particles furnish cohesion by means of
extremely thin film of moisture which they retain after
the thicker film of capillary moisture has evaporated. Some
binder soil is necessary to hold the aggregate together
during construction so that satisfactory compaction can

be obtained. However, only a small portion is required

and an excess is detrimental to a surface of this type.

FIELD TESTING TROCEDURE

It is realized that only one sample from a pit is
not representative, therefore, the material must be listed
on the Job during excavation and production to insure a
uniformly satisfactory base course. To accomplish this
there should be a small field laboratory at the plant site
and the inspector should test several samples of the finished
product each day as well as the different types of materials
encountered in the pit. The inspector should be furnished
with a field soil kit of laboratory equipment, and a manual
of test procedures for the field tests.

The soil sample is first dried, weighed, then allow-
ed to soil in water long enough to shake all of the soil
binder. It is important that the sample be dried before
any slaking is attempted. After the slaking, and8 inch
40 mesh sieve with two inch sides is placed in a large
' clear pan and the free water peoured of the sample through
the screen. The sieve is agitated up and down until all
of the soil binder appears to have passed through the meshes.
The sieve is then held above the water and the remaining
material there in washed by pouring over it a small amount
of clear water. This retained material is then placed in-
to a separate pan and another batch of the slaked material

placed on the screen as washed as before. After the total

43

'sample has been washed,aany water present in the retained
material is poured out and the materials been dried and
weighed. The percentage of material larger than 40-mesh
is calculated as
100 x day wt. of material retained on 4Q-mesh
or ginal dry wt. of’totalfsample
and Percent Soil Binder 8 100 - Percent retained on 40-mesh.

A portion of the dried soil is put into a stone mor-
tar and broken down with a stone pestle until all lumps
are smaller than 1/16 inch in diameter.) The material is
then sieved on a 40-mesh sieve and the retained portiori re-
turned to mortar. A rubber covered pestle is now used to
take the remaining material down to just pass the 40-mesh
sieve without fracturing any of the individual grains.
It is then thoroughly mixed, and is referred to as 'prepared

sample' hereafter.

The liquid limit test is then made using the hand
method. The hand method is preferred for field work because
(1) only one moisture content sample is put up, (2) a big
saving in total time consumed is effected (5) expence of
device is eliminated and (4) with a trained and experience
operation that method appears to give as accurate and consis-
tant results as can be obtained by the liquid limit device.
Apparatus: --- Two evaporating dishes of east aluminum, one

stainless steel spatula with 4 inches blade, one grooving

tool, 50 c.c. graduated burette with slant, balance and

weight box.

About 15 c.c. of water, slightly more for a day type
and a little less for a sandy type soil, is placed in an
evaporating dish and dry soil added to it until practically
all of the free water has been absorbed. The mixture is
then thoroughly mixed for several minutes using the broad-
side of the spatula. Additional increments of dry soil are
then added to the mixture, and the material is thoroughly
mixed after each addition of soil. When the material at-
tains the consistency of a fairly thick paste, it should
be tested to see if the end point has been reached. The
material is then pressed against one side of the dish, smooth-
ed off in a layer about 5/8 inch thick, and a clean groove
cut in the soil with the grooving tool. The dish is then
held in one hand, with the groove on the outside and struck
lightly against the heel of the other hand ten times. If
the groove does not close with ten blows, more water is
added and thoroughly mixed. If the groove closes with less
than ten blows, more dry soil is mixed in thoroughly and
the testedrepeated. When the groove Just closes on the
tenth blow, a large portion is placed in a moisture can,
weighed, overdried to constant weight, and weighed again.

Liquid Limit = Wt. of Wet Soil and can - Wt. of dr soil and can,
wt. of dry soil and can - Wt. of can

THE PLASTIC LIMIT

The plastic limit of a material is the minimum
moisture content at which the portion of the material pass-
ing the N0. 40 mteve may be rolled in threads 1/8 inch in:
diameter without the thread breaking into pieces. A sample
weighing 55.5 gung is taken from the 'prepared' sample
and placed in an evaporating dish. The water level in the
burette is recorded and water is added from the burette
in an amount to bring the soil to a slightly plastic mass
after the material and water have been thoroughly mixed. The
ground glass plate is slightly moistened with a damp earth
and the moist material from the sample is shaped into a ball
and rolled between the palm of the hand to form the mass
into a thread. If the material is too dry to permit rolling
into a thread 1/8 inch in diameter increments of water are
added from the burette and mixed until thennathaial can be.
rolled to a thread of the specific size without breaking
into pieces. The final burette reading is taken. The P.L.
is equal to three times the number of c.c. of water that

have been added to the dry sample of minus forty material.

SIEVE ANALYSIS

The sieve analysis test should be conducted on the
original sample. The text has been described under soil
tests. A simplified step by step procedure for work under

field conditions is as follows: ---

1.
2.

4.

5.

6.

7.

46

The sample is dried to a constant weight.

The total weight of the dried sample is obtained and
recorded and the sample placed in a pan for washing.
The sample is washed under a stream of water until the
water becomes clear.

After washing, the sample is dried for sieve analysis.
Sieve analysis is run on the sample, using the differ-
ent sieve sizes required. Special care is taken to
shake all sieves to refusal.

The material retained on the largest screen is placed
in the scale pan, the weight read and recorded. The
material retained on the second sieve is added to that
from the first sieve, the weight recorded, and so on
through the entire net of sieve.

The percent retained on each sieve is computed on the
basis of the original total weight and recorded to the

nearest whole percent.

LINEAR SHRINKAGE TEST

The field test for the 'Linear shrinkage' of a soil

binder is the percentage of shrinkage, on the basis of

original wet length, acquired by a soil bar in drying from

its liquid limit down to its shrinkage limit (the moisture

content at which all shrinkage cases). The preliminary

shrinkage of soil containing water in excess of the liquid

limit is in a downward direction. Therefore the linear

shrinkage of a soil bar as measured in the test will not
be materially changed if the specimen is moulded with an
amount of water in excess of the liquid limit. In fact
more accurate result would be obtained from speciments
mixed as described below rather than those made at exactly
the liquid limit consistency. Either the dry material or
the wet soil binder may be used in preparing specimen for
the test but the dry material is preferable. If a dry
material is used, about one third of a cup of water, more
for a clay type and less for a sandy type material, should
be placed in an evaporating dish and the dry soil added to
and thoroughly mixed in with the water until a consistency
slightly more fluid than the liquid limit is reached.

The material is at the pr0per consistency for mould-
ing when a slight tilting of the dish or more light Jar
will close the groove made by the grooving tool. -Cast alumi-
num moulds, with removable end plates, é“ wide, &' deep and
5 indhes long are used. The inside of the mould should be
thinly greased. The wet soil mixture should be placed in
moulds in small increments and worked with a spatula to
remove all air bubbles. As soon as the mould has been pro-
perly filled, the excess should be struck off and the speci-
men smoothed down level with the top of the mould. The
specimen should be placed in an ovemiafter the specimen form-
ed, provided that is not very plastic type of soil. Speci-

men formed of plastic soil is. those with a P.I. greater

than 15, should be dried at less than 140° F. When the

specimen has dried to constant length, the loss in length

is measured to nearest 1/40 Oflrhnifneh.

The percentage Linear Shrinkage : 100 x Loss in Length
Original length

FIELD MOISTURE EQUIVALENT

This is the minimum moisture content expressed at
a percentage of the weight of the oven dried soil, at which
a drop of water placed on a smooth surface of the soil
will not immediately be absorbed, but will instead spread
out over the surface and give it a shiny appearance. The
soil is mixed with water until it will 'ball up' slightly.
A small area is smooth and off with the spatula and a drop
of water allowed to fall on it. While the drop remains on
the surface it appears shiny and when it is absorbed this
luster is lost. The time required for the water to be
absorbed is noted until the drop is absorbed in just 50

seconds. The moisture content is then determined.
CONTROL OF PROPORTIONS DURING CONSTRUCTION

The materials are being delivered to the roadway
the Engineer should (1) Determine the moisture content of
the materials to insure that the proportions by dry weight
are correct to result in a mixture that will meet specifications.
(2) Conduct screen analysis and when necessary P.I. test

on at each 100 tons of individual materials to determine

49

if the proportions being delivered will meet the specifica-
tions for gradation and plasticity index for the project.
(5) Make adjustments in prOportions of the mix when the gra-
dation on plasticity of the materials change enough to ef-
fect the final mix.

MIIing: --- If a blade-mix is used it may be necessary

to conduct an occasional test to determine whether or not
excessive amounts of roadway soil are being bladed into the
mix. Spotted sections which contain excess coarse aggregate
or an insufficient quantity of filter or binder will ravel

on under truck traffic.
EXECUTION OF WORK UNDER LOCAL CONDITIONS

In 1946 about 25 miles of stabilized road was con-
structed as an experimental measure by the soil stabiliza- '
tion division (Lahore, Pakistan) under Mr. S. R. Mehra.

The following was the procedure adopted in the execution
of the work.

1. Collection.2£‘§gilg: The quantity of each type of

soil required in each stock (two to four furlongs as the
case may be), was worked out, from the statement of the De-
sign of Mixtures, and the requisite quantities were collected
at the specified points.

2. Pulverizing g; ggilg: The soils were then broken, with

the backs of the spades or rammers as convenient, to such

a state of fineness that about 80 percent of the soil was

under 5/16 inch size.

5. ‘2 y Mixing End Stacking: The soils or soil-plus-aggre-
gate were then thoroughly mixed in the dry state and made
out into a stack 15 to 18 inches in height. The top of
that stack was carefully levelled, the ground on which it
stood, having been levelled before hand.

. 4. Checking up 3; gixgd stacks: A representative sample
was taken from the stack and analysed in the field labora-
tory to check up the sand contents and P.I. When the
mixture was formed satisfactory the stack was ready for
mixing. If the mixture was found not up to the specifica-
tions, the necessary changes were made and the mixture was
retested. .

5. Addition 3; moisture: On the day proceeding the date
for laying the mixture on the road, a representative sample
was taken from each stack and the contained moisture was
determined in the field laboratory. The additional mois-
ture to be added to each stack to make up its optimum
moisture was then worked out in gallons per oft. of mix
after allowing for evaporation and absorption by the brick
aggregates (if used). The evaporation losses change from
time to time due to change of weather, and were periodical-
ly determined as required. The necessary moisture was

then added towards evening and allowed to seep through the
stack overnight.

6. Laying: In the morning the wet mix was sliced out of

the stack in small lots, mixed as required and laid on

the road, in template both longitudinally and crosswise.
The wearing course was laid after the lease course had been
dried out for a day or so. The lease course was thus a
couple of days ahead of the wearing course. After laying
the wearing course about 10 percent of the aggregates saved
from the total quantity, was spread on the surface. (a)
Base course. The base course was rolled by means of sheep
foot rollers. Locally manufactured sheep foot rollers

were used and an average of 50 trips of rollers were re-
quired to consolidate a 10 ft. width of road. The rolling
was finished off with a flat roller 5-6 tons. The compac-
tion obtained was checked by means of the dry bulk density.
(b) Wearing Course. The wearing course was rolled with
flat 5 wheel rollers 5-6 tons in weight. Rolling was con-
tinued till the wheels do not make an appreciable impression
on the surface. A heavy sprinkling of water was given to
the surface and left overnight. In the morning the surface
was again rolled to finish.

7. Curing: The surface was kept heavily sprinkled with
water for 4-5 days, and closed to traffic. After this the
road was opened to traffic but water was sprinkled for an-
other 10-14 days were required till the surface gets pro-
perly set.

8. Maintenance: Maintenance consisted in digging up the
wearing course where a pot hole was about to form and putting

it back by adding requisite moisture with 1 percent molasses

on the weight of soil added to it. The percentage was
roughly obtained by mixing 5 parts of water with one
part of molasses, and adding enough of the solution to
the soil mixture, so that it makes it just moist enough
to be readily pressed into a ball in the hand.

CHAPTER III
PORTLAND CEMENT STABILIZED ROADS

Soil-cement is a simple, intiinate mixture of soil
with measured amounts of Portland cement and water; compact-
cd to high density. Three basic control factors govern ’
successful construction. These are (1) adequate cement

content; (2) pr0per moisture content; (5) proper density.

The quantity of cement and water to add, and the
density to which the mixture must be compacted are deter-
mined by tests before construction starts, thus assuring
success of completed pavement. The cement acts as the
binder, and by chemical action with water, cements the
material into a hardened mass. The water serves two purposes,
(1) it assists in obtaining maximum compaction ie. density
by lubricating the soil grains, and (2) it hydrates the
cement so that the mass can be hardened. This first pur-
pose is, of course, important since an intimate contact be-
tween cement grains is necessary, but the second is more
important since without sufficient water the cement cannot
hydrate effectively and the soil-cement will not harden
prOperly. During the mixing of soil, cement, and water,
the mass acts similarly to a soil with only minor differences
'in colour and texture due to the presence of the cement.

But after the damp mixture has been packed to a high density
the cement action becomes more obvious as it takes up water

hydrates, crystallizes, and hardens the mass. Each day the

54

cement hydration continues and the soil cement becomes harder.

Wet-dry, freeae-thaw, and compressive strength tests
are made on specimens moulded of soil-cement mixtures at
optimum moisture and maximum density to determine the quantity

of cement needed with the soil.

Construction then starts. First, if the soil con-
tains much silt or clay, it has to be searified and the
lumps broken down after which it is shaped with a blade
grader. Cement is spread over the area in the pr0per pro-
portion and mixed in with the soil. The operation is called
'dry mix'. Water is added in increments each being mixed
with the soil-cement before the next is added. This opera-
tion is called the 'damp mix'.. Water must be controlled
with reasonable limits since too little water will not pro-
perly hydrate the cement or permit compaction to maximum
density, and too much water will make the mixture too wet
to pack out. When the proper amount of water has been add-
ed and intimately mixed with the soil-cement, the damp
mixture is packed out with sheep foot rollers and smooth
steel rollers. Maximum density test is determined on the
soil-cement mixture taken from construction towards the
conclusion of the damp mix. Traffic should not be allowed
until some t pe of straw or earth cover has been placed on
the top to protect it from abrasion and to hold the moisture

in the compacted soil-cent. After seven days the cover

is removed and the soil-cement swept clean. At this
time it can take considerable traffic without much abrasion,
but before it is open to continuous use, a light bituminous

wearing surface may be placed where possible.

MATERIALS
Generally suitability of soils for soil-cement work
is judged (l) on the basis of their gradation, (2) and on
their position in the soil profile.

GRADATION

Soils can be divided into three groups.
1. Sandy and gravelly soils with some fines sand and
gravels, crusher run limestone and some lime-rocks) have
the most favourable characteristics for soil-cement con-
struction. They are readily pulverized, readily mixed
with the cement and water, can be used under greatest range
of weather conditions, and easily finished off to a smooth
surface having good wearibility.
2. Sandy soils without fines have equally good character-
istics for soil-cement construction as soils in group no. 1
except for packing and finishing. Changes in gradation
will be necessary in the majority of cases. Otherwise
larger quantities of will be required to obtain the same
results. These soils are likely also to be 'tender' and
to require attention during the final packing and finishing
to obtain a smooth, light surface. Without a bituminous

56

surface, they may not have high wearibility as unsurfaccd
soil-cement made from soil in group I.

5. Silty and clayey asoils make satisfactory soil-cement
but those containing the higher clay contents require

more experience to pulverize than other soil. Construction
with these souls is less independent of weather conditions.
Soils that are difficult to pulverize at a dry moisture
content, many times can be made mellow and broken down
readily after water is added and permitted to soak in.

In most instances when soils in group (1) and (2) are avail-
able close by. They should be burrowed and placed on top
of soils in group (5) and used for building the soil cemnnt
road. At least sufficient quantity to build up a six-inch

compacted thickness of soil-cement should be placed.
SOIL PROFILE

In some instances, the gradation of the soil is
secondary to its chemical make up in so far as its reaction
with cement is concerned. This is because some types of
surface vegetation deposit organic material in the surface
soil which is harmful to cement. Thus surface soils with-
out organic matter are likely to react better with cement
than surface soils which contain organic matter. In general
it can be assumed that the poorest reacting surface soils
will occur in areas where vegetation is trees, and the

rainfall relatively heavy. Then are usually dark coloured.

57

In areas where rainfall is light and natural vegetation
'is grass, surface soils, even though dark, generally react

as well as the subsurface soil.
WATER

The water used in soil—cement should be relatively
clean and free from harmful amounts of alkalies, acids or
organic matter. Water fit to drink is satisfactory. If
fresh water is not available, other water can be used with
caution. If there is any question whether water from small
creaks, slow moving rivers, or swampy areas is suitable,
simple test can be made by mixing cement and water together
to form a stiff paste and the compacted mixture should

be quite hard in about 24 hours.
ESTIMATE OF CEMENT AND WATER

Cement and water requirements vary with each soil.
Cement may be estimated at 10 percent by volume (0.45 bags
per square yard of pavement 6 inches in compacted thickness);
but actual quantities will vary from 7 percent to about
16 percent by volume. Water quantities can be estimated
at 9 gallons per square yard of pavement 6 inches in com-
pacted thickness. The actual quantity of water will vary
with the Optimum moisture content of the soil-cement, the
moisture content of the soil at the start of processing,

and the rate of evaporation during construction.

STANDARD SOIL-CEMENT TESTS

Laboratory research and field experience has shown
that soil can be hardened by the addition of portland cement
to produce a structural material suitable for low cost
roads. Soils under different conditions behave in various
ways. The manner in which they react is shown by labora-
tory tests. The success in the field, therefore, depends

upon these laboratory tests.

Laboratory procedure consist of pulverizing the soil
so that it, exclusive of gravel and rock, passes a No. 4
sieve. Moisture density relations are then obtained for
this soil and for soil-cement mixtures of various cement
contents. Specimens containing various cement contents
are then fabricated at optimum moisture content and maxi-
mum density and tested in the wet-and-dry and freeze-and
thaw tests to determine the quntity of cement required to
produce a structural material that will pass certain test
criteria. These tests determine, (1) the proper quantity
of water to add to soil-cement mixture to obtain maximum
effectiveness from the cement; (2) the proper density to
which the damp soil cement mixture should be compacted to
obtain maximum effectiveness from the cement; and (5) the
proper quantity of cement required to harden a soil adequate-

ly and economically.,

MOISTURE DENSITY TESTS

This test is intended for determing the relationship
between the moisture contents of soil-cement mixtures and
the resulting densities (oven-dry weight per cubic foot),
when the soil-cement mixture is compacted in the laboratory,
before cement hydration. During the time that soil-cement,
and water are being mixed, there is a distinct change taking
place in the mixture. Moisture-density relations of a soil
cement mixture will vary slightly as a result of this chemical
phenomenon and the partial cement hydration that has taken
place during damp mixing. These effects will be noted
as an increase in the maximum density of the soil-cement
mixture as the damp mixing time increases. For this
reason, specifications for soilycement construction require
that moisture density relation be established in the field,
using soil-cement taken directly from the construction

toward the end of the damp mixing procedure.

Choose the cement contents by volume. Before deter-
mining thc moisture density-relation of soil-cement mixtures
it is first necessary to estimate the cement-contents by
volume that are to be investigated in the wet-dry and freeze-
thaw tests. The cement contents are usually selected in
and ascending order of 2 percent increments, such as 6, 8,
and 10 percent. Calculations for converting cement contents
by volume to cement contents by weight, and for determingng

the quantities of soil and cement required for making the

60

moisture density is 105.5 pounds per cft.; therefore,

a moisture density test specimen will weigh about 105.5 a
50 .

5.52 pounds. Five individual moisture-density tests are
made and each sample weighing about 100 grams will be taken.
So the total specimen we will take would be 5.52 pounds
plus 500 grams . 4.6 pounds. Assume the hygroscopic mois-
ture content of soil is 6 percent or 4.6 x 1.06 . 4.88
pounds of air-dry soil is weighed out. The cement content
by volume to be investigated is 8 percent. The next step
is to convert the cement by volume at maximum density and
Optimum moisture to a weight basis to permit assembling
the mixtures with ease and accuracy. Eight percent-cement
by volume is equivalent to 0.08 x 94 or 7.52 pounds of
cement per cubic foot of soil-cement.

This is equal to ( 7.52 ) 100 or 7.68
percent cement by weight of oven-dry-soil. Therefore

4.6 x 7.58 x 454 - 164 grams cement will be used with
T
4.6 pounds of soil.

The A.S.T.M. has recommended the following procedure
for determining the moisture density} The air dry soil shall
first be pulverized to pass a No. 4 sieve so as to separate

the soil particles without reducing the particle size. The

 

1American Society for Testing Materials. 1944. Methods
of Test for Soil-Cement Mixtures (D 558-40T) Philadelphia, Pa.

required cement shall be added to the pulveriged soil. The
test shall be performed only on that portion of the soil-
cement mixture which will pass a N0. 4 sieve. The thoroughly
mixed soil-cement sample shall be immediately compacted

in the mould in three equal layers, to give a total compacted
depth of 5 inches; each layer being compacted by 25 blows

of the rammer dropping free from a height of 12 inches above
the elevation of each compacted layer. During compaction
the mould shall rest on a uniform, rigid foundation weigh-
ing 200 lb. or of equivalent rigidity. The blows shall be
uniformly distributed over the surface of the layer being
compacted. After compacting, the collar shall be removed
and the top carefully trimmed to the exact height of the
mould with a steel straight edge toproducc a specimen
approximately 4.6 inch in height and having a volume of 1/50
cu. ft. The weight of the compacted soil-cement mixture
shall be determined, the material removed from the cylinder,
sliced vertically in the center and a lOO-g. sample taken
from the center, weighed immediately dried in an oven at
1100 C. for at least 12 hours or to a constant weight.

This procedure establishes the moisture-density relation

of the air-dry soil-cement mixture.

The soil-cement mixture shall be again finely pul-
verized,,so as to separate the particles without reducing
the particle size, to pass a No. 4 sieve and a small incre-

ment of moisture carefully added and thoroughly mixed to

insure uniform distribution. .Thcn the moistened and pul-
verized material shall be compacted in the mould in three
layers as explained above, weighed and a moisture determina-
tion made to establish the moisture-density relation for

a slightly moistened soil-cement mixture. The soil-cement
mixture will again be finely pulverized, so as to separate
the soil particles without reducing the particles size,

to pass a No. 4 sieve and additional increment of water
added and the same procedure followed of mixing, compacting
in the mould, weighing, and making moisture determinations
until the moisture content of the soil-cement moisture
reaches a condition where it is difficult to pulverize the
moistened materials, or it has a moisture content near the

liquid limit.

Calculations:
~ The moisture content and oven-dry weight of the mix-
ture as compacted shall be calculated by macans of the

following formula.
Moisture percent 3

Wet wt. of soil cement - Wt of oven dried soil-cement x 100.
Wt. of oven dried soil-cement

 

Dry weight (Per cu. ft. of soil-cement as compacted)
: Wet Wt. in 1b. Per cu. ft. x 100.
Percentage of moieture plus 100
HOULDING SPECIMEN FOR WETBDRY AND FREEZE-THAN TESTS

Calculations are made for the quantities of soil,

cement and water necessary for moulding test specimens.

The calculated quantities of air-dry soil and cement are
weighed out and spread on a steel tOp table and lightly
troweled to facilitate dry mixing. The designed quantity
of water in sprinkled uniformly over the soil-cement which
has been spread over a steel table to a depth of about 5
inch. Mixing is of uniform colour. If the soil is quite
sandy the water will be mixed in easily, however, heavier
textured soils require additional treatment. Moisture dis-
tribution in the heavier textures soil is facilitated by
pounding the semi mixed soil, cement, water into a container
8 to 10 inches in diameter and about 2% inches high. A
metal hand temper is used in this iperation. The mixture
is permitted to set in the semi-compacted condition 2 or

3 minutes. In some instances it may be well to repeat

the above procedure to insure uniform distribution of

,moisture.

The test specimen is compacted with the same mois-
ture-density equipment used to make moisture density test.
After the specimen is moulded, the collar used to protect
the rim of the mould is removed after cutting the specimen
down alongside the collar and the top of the mould with
a knife to prevent clipping. The surface of the specimen
is levelled with a straight edge. The weight of the
moulded specimen is then obtained and used in conjunction

- with the moisture determination to compute the dry weight

64

and cement contents by volume of the moulded specimen.

The test specimen is carefully removed from the mould. As
the specimens are moulded they are placed in an atmosphere
of high humidity and the cement is allowed to hydrate for

7 days before starting in the wet-dry and freeze-thaw test.
WET-DRY TEST2

At the end of 7 day storage period in an atmosphere
of high humidity, the specimens are submerged in tap water
at room temperature for a period of 5 hours, removed and
no. 1 specimen measured and weighed. No. l and No. 2 speci-
mens are then placed in an oven at about 71 c. for 42 hours,
after which they are removed, and both specimens weighed,
and No. l specimen measured. Specimen No. 2 is then given
two firm strokes on all areas with a wire scratch brush.

In completely covering the total area of the specimen twice,
approximately 18 to 20 vertical strokes of the brush are
required on each end of specimen. The specimen is again
weighed after brushing.’ This procedure constitutes one

cycle of wetting and drying (48 hours). The specimens are
then again submerged in water and the wetting and drying
cycles continued. Twelve cycles of wetting-drying complete
the test. The volume and moisture changes and the soil-cement

losses of the specimen are be calculated as follows: The

 

2American Society for Testing Materials, 1944. Methods
of Tests for Soil-Cement Mixture. (D 559-4OT). Philadelphia, Pa.

65

difference between the volume of specimen No. l at the time
of moulding and subsequent volumes shall be calculated as

a percentage of original volume. The moisture content of
specimen No. l at the time and subsequent moisture contents
shall be calculated as a percentage of the original over-
dry weight of the specimen. The soil—cement low of speci-
men No. 2 shall be calculated as a percentage of the origin-

al oven-dry weight of the specimen.
FREEZE-THAN Tssr5

At the end of 7 days storage period in an atmosphere
of high humidity, water saturated felt pads, lilotters or
similar absorptive material are placed between the specimens
and the specimen carriers. The assembly is placed in a
refrigerator having a constant temperature not warmer than
-28 C. {-10 F.) for 22 hours. The specimens are then re-
moved and the No. l specimen (volume and moisture change
specimen) is weighed and measured, and both specimens placed
in the moist room or air in a suitable covered container
to thaw. The absorbent pads under the specimens shall have
access to free water to permit absorption of water by the

specimens by capillarity.

After a 22 hour thawing period both specimens shall

be weighed and the No. l specimen measured. Specimen No. 2

 

zlmerioen.$ooiety For Testing Materials. 1944. Methods
of Test for Soil-Cement Mixtures (D 560-4OT) Philadelphia, Pa.

(soil-cement loss specimen) is then given two firm strokes
on all areas with the wire scratch brush. To completely
cover the specimen twice, 18 or 20 vertical strokes of the
brush are required on the sides of the specimen, and four
strokes on each end. The specimen is weighed again after
brushing. This procedure constitute one cycle (48 hours)
of freezing and thawing. The specimens are then replaced
in the refrigerator and freezing thawing period. At the
end of each thawing period and after brushing, the speci-
mens are turned over, end for end, before replacing on the
wet pads. Twelve cycles of freezing-thawing complete the
test.

Failure of many of the silt soils and some of the

' clayey soils is caused by sealing of specimen on sides and
ends. In certain instances it is necessary to use a sharp
pointed instrument to loosen this scale, in as much as the
normal brushing after thawing sometimes fail to remove it
because of the structure of the scale and the surface tension
of the water film between the scale and the remaining portion
of the specimen. Calculations are exactly the same as for

wet-dry test.

FIELD TESTING

The following tests are conducted in the field dur—
ing construction: --- (1) field compaction (2) pulverization

tests (3) sieve analysis (4) density test.

FIELD COMPACTION TEST

The procedure in use in conducting the standard

compaction test is as follows.

(a)
(b)
(c)
(d)

(e)
(I)

(s)

(h)

(1)

Obtain a 40 to 50 pound of sample of soil

Mix the sample thoroughly

Weight out 6 or more 6 pound samples.

Weigh out one 50 ounces or 100 grams sample for mois-

ture content determination.

Determine the moisture content

Compute the dry weight of soil in a six plus 61 pound

sample.

Compute the wet weight of soil (based on dry weight

sample) for the various moisture contents (at increments

of 2 percent) to be used in determining the compaction

curve.

Make compaction tests at the various moisture contents

necessary to obtain the compaction curve. Immediately

before mixing and compacting, each sample should be

brought to the prOper moisture content by adding mois-

ture. The moisture content of the soil should be uni-

formily distributed by thorough mixing before being

compacted in the mold.

Compact the soil as follows:

1. Place sufficient soil on the mould to fill the
cylinder (lower section of the mould) approximately

one-third full after being compacted.

(J)
(k)

(l)

(m)
(n)

2. Compact the soil, with 25 blows of the compaction
hammer distributed evenly over the layer.

5. Add soil and compact two more layers in a similar
manner. The third layer should extend approximately
&" above the cylinder after the collar has been
removed.

4. Remove the collar and cut soil flush with the top
of the cylinder, with the trimming knife

5. Turn the mould on its side and trim the excess
soil from the bottons of the cylinder.

Remove the cylinder from the mould and weigh.

Cut the cylinder into halves lengthwise and obtain a

representative moisture sample of all lifts from the

centre of the specimen. Dry this sample for moisture

content determination.

Knowing the moisture content, compute the dry weight

of the soil in the cylinder.

Compute the dry density

Plot the dry density as the ordinate, against the

moisture content on the abscessa.

4Quantity of Cement for Material which does not con-

tain aggregate retained on the No. 4 Sieve. Before compac-

tion tests can be conducted on the soil-cement mixture, it

is necessary to determine the percent of cement to be added

 

4Kansas State Highway Commission, 1941. Soil and Stabi—

ligation Manual for bease conrse construction. Austin, Texas.

 

[trip int ‘1 I.

to the raw soil. If the quantity of aggregate retained

on No. 4 sieve is quite small, less than 5 percent, it may
be neglected and the percent of cement to be added to the
new soil may be calculated as follows: Required cement
content by volume of the compacted soil-cement mixture 3
10 percent.

Standard compaction value of raw soil to be treated = 108D.G.F.
lot per cubic foot of cement : 34 pounds.

Assume wt. of the soil-cement mixture 3 108 P.C.F.

Then one cft. of soil-cement mixture requires 0.1 cft of
cement = 94 x 0.1 3 9.4 lb. and 108 .9,4 = 98.6 lb. of dry
soil. Then to determine the percent of cement by weight,
ditide the weight of cement by the assumed weight of a cubic

foot of the soil-cement mixture.

or ( 9.4 1100 a 8.7 percent of cement by weight.

Then to make a soil-cement mixture having a total weight
of 7 pounds it will require ‘- 7 x 0.087 = 0.609 pounds of
cement and 7.000 - 0.609 = 6.391 pounds of dry soil. If
the sample obtained from the road contains 12 percent mois-
ture then it will require 6.391 J 1.12 = 7.158 lb. of
moist soil to provide 6.391 pounds of dry soil. The

soil and cement should be thoroughly mixed until a uniform

colour is obtained.

Quantity of Cement for Material Containing Aggregate Retained
on the No. 4 Sieve. Soil that contains an appreciable

quantity of aggregate needsonly a sufficient quantity of

7O

cement to the total material to obtain durability of the
portion of the sample passing the No. 4 sieve. For this
reason and also because of the quantity of plus 4 material
in the roadway may change after preliminary samples have
been taken, all durability test in the laboratory are con-
ducted on the portion of the sample that pass the No. 4
sieve. Therefore, all quantities of cement shown in the
soil reports and in the specifications are based on the

minus 4 material.

If, after shaping operations, the soil to be treated
contains an appreciable quantity of gravel retained on
the number 4 sieve, a sieve analysis should be conducted
on each sample of the soil taken for compaction test to
determine the percentage or aggregate retained on the No.
4 sieve. The calculations for this test should be based

on the total dry lot of the sample tested.

After the quantity of plus 4 aggregate has been de-
termined, the quantity of cement to be added to the raw
soil for soil-cement compaction test and the roadway dur-'
ing construction, shall be calculated. Required cement
content of the minus 4 material in the preliminary labora-
tory sample = 10 percent by volume,of the soil-cement mix-
ture. Compacted density of the minus fifl raw soil construc-
tion sample - 110 P.C.F. Aggregates retained on No. 4

sieve in the raw soil construction sample 3 30 percent by

71

weight. Specify gravity of the plus 4 material = 2660.
Then one cft. of the preliminary soils-cement sample con—
tained 0.1 cu. ft. of cement and 0.9 cu. ft. of minus 4
raw soil, or the cement contents based on the volume of
raw soil = 0.1 x 100 = 11.1 percent.

One cubic foot of the raw soil construction sample
contains 0.30 x 100 I 33 lbs. of plus 4 aggregate which
occupies

33 I 0.203 cu. ft. of volume
. x .

Then the construction sample contains 0.203 cft of plus 4
aggregate and 1.000 - 0.203 8 0.797 cu. ft. of minus 4 ma-
. terials '

Since the laboratory tests conducted on the preliminary
sample showed that it required 11.1 percent by volume of
minus 4 raw soil to obtain durability, the construction
sample will require 0.111 x 0.797 8 0.088 cu. ft. of cement
to harden the cubic foot of raw soil Then the volume of
material in the construction sample will be

0.203 cu. ft. of plus 4 aggregate
0.797 cu. ft. of minus 4 aggregate
0.088 cu. ft. of cement
12—09? cu. ft. of total material
This requires 0.088 cu. ft. of cement for durability or
by volume of soil-cement mix equals:
0.088 g 8.09 percent, the required cement content for

1.088
compaction tests and for the material in the roadway.

72

PULVERIZATION TESTS

At the conclusion of Pulverization operations, samples
of each type of soil being treated shall be obtained for
pulverization tests. The samples shall be thoroughly mixed
and quartered or split to result in a sample weighing approxi-
mately 7 pounds. The seven pound sample shall be screened
over the No. 4 sieve, and the two portions placed in separate
pans and dried. Each of the dried portion shall be weighed
and the percentage of the sample retained on the No. 4
sieve shall be calculated, retained on the No. 4 sieve
shall be calculated, h—ased on the dry weight of this entire
sample. The percentage of soil retained on the number 4 sieve

g 2£y_weight of soil retained on No. 4 sieve x 100
Total weight o?:§ample

SIBVE'ANALXSIS

Where an appreciable quantity of aggregate occur
in the soil to be treated, a sieve analysis should be con-
ducted to determine the percentage of material retained
on the No. 4 sieve. A portion of the sample obtained for

standard compaction test shall be used for this test.

The sample to be tested, weighing approximately
seven pounds, shall be dried to constant weight and all
lumps of soil shall be broken down to pass the number 4
sieve. The total dry wt. shall then be determined and the

sample shall be screened over the No. 4 sieve. The portion

73

retained shall be weighed and the percentage retained shall

be calculated as follows:

= Wt. of material retained x 100.
drywt. of total sample

 

Moisture Test --- The sample for moisture test should be

thoroughly mixed, guartered down to an apprOpriate size

and a moisture test conducted.

1.

2.

3.

4.

5.

Weigh carefully and record weight if the sample has

been accurately weighed where first obtained on the fill.
This step in unnecessary.

Place sample in a pan and spread to permit uniform dry-
ing. Set pan in a second pan to prevent burning of

soil and place on stove.

Dry to constant weight. The temperature of the soil
should be approximately 110° C (2300 F). Stir constantly
to prevent burning, but not vigorously enough to cause
dust loss.

After the sample has been dried to constant weight,
remove from stove and allow to cool to prevent error

in weighing. Do not cool sufficiently to allow soil

to absorb an appreciable amount of hygroscopic moisture
weigh dried sample.

Compute moisture contents as follows.

Percent moisture - Wt. of wet soil - Wt. dry soil x 100
Wt. dry soil

DENSITY TEST4

Tests to determine the density of the subgrade prior

to pulverization and after the base course is compacted
shall be determined by sand method as outlined below.
Sand Method Density Test --- This method of density deter—
mination is based on the fact that if a certain wt. of clear
,dry sand is poured from a given weight height into con-
tainers of approximately same size and shape, it will oc-
cupy the same volume of space. Then, if a known weight
of sand whose unit weight has been determined is poured
into and hole, thevolume of the hole can be determined.
Thus, if it requires 10 lbs. of sand, whose unit weight
is 100 lbs. per cu. ft., to fill a hole of this volume of
the hole is

10 s 0.10 cubic ft. Then if dry weight of

IOU-

the soil removed from the test hole is 11 pounds the

density of the soil 3 wei ht g 11 . 110 lbs. per cu. ft.
vqume 0710'

It may be desirable in some instances to dry only a small
portion of the each soil removed from the test hole for
moisture content determination. If this is done, the dry
weight of the sample must be calculated from the wet weight
and the moisture content before the dry density can be de-
termined. This may be done as follows: ---

Dry weight of sample 3 Wet wt. sample x 100
1000 - moist. content sail

or let wet weight 3 14.2 lbs.
and moisture content - 15 percent

Then: Dry wt. of sample = 14.2 x 100 - 12.3 lbs.
IIE‘

This dry wt. may then be used in computing the dry

density.

Method of conducting: ---

(a)

(b)

(c)

(d)

(e)
(f)
(6)

Determine wt. per cu. ft. of sand to be used for test

as follows:

1. Deposit sand in one tenth cu. ft. scale bucket
by means of the one gallon measure with pouring
spout. Hold pouring spout approximately two inches
above the top of the bucket. Deposit sand at a
uniform rate.

2. Strike off excess sand flush with top of bucket
by means of a straight edge. In striking off ex—
cess sand, do not Jar bucket and cause sand to settle.

3. Weigh and record weight of Sand in container

4. Compute and record weight per cu. ft. of sand

Remove all loose soil from an area large enough to

place the 14 inch box flat on the surface.

Bore a hole (through hole in the box) through the full

depth of the compacted material

Place all soil cut from the hole in pans including

any spillage caught in the box. Use a small can and

remove all loose soil from the hole. Extreme care
should be taken not to lose any soil.

Weigh all soil removed from the hole.

Th sample thoroughly

Take out a sample immediately for moisture determina—

tion. Place remaining soil in a clear sack until the

test has been completed.

(h)
(1)

(J)
(k)
(l)

Weigh sufficient sand to more than fill test hole.
Deposit sand in hole by means of one gallon measure.
Hold pouring spout approximately two inches above the
top of lid. Bring the sand almost flush with the sur-
face and complete the pouring by means of a small can
until it is flush with the surface when tested with

a straight edge.

Weigh remaining sand

Determine moisture content

Compute dry density

CONSTRUCTION

The following outline shows the usual sequence of

construction operations and the tests and calculations

necessary for the proper control of construction.

1.

2.

Shaping
a. Determine density of soil in grade

b. Sample for:

(1) Percentage aggregate retained on No. 4 sieve
(2) Compaction test

(a) Raw soil

(b) Calculate quantity of cement

(c) Soil-cement mixture

c. Calculate depth of cut.
Pulverization

a. Sample for:

(l) Pulverization
(2) Moisture content
b. Calculate cement spread
3. Spreading Cement
4. Dry mixture
5. Add water
6. Moist mixing
7. a. Sample for moisture test
7. Compaction test for:
a. Check density and moisture
8. Finishing
a. Final density
b. Moisture test

METHODS OF MIXING

Several methods of mixing the soil, cement and water
have been used successfully in constructing this type of
base. These methods may be divided into "Road mix" and
"Machine Mix" methods. The 'Machine Mix' method may be
subdivided into stationary and travelling plants and the
latter type of plants may either pick up material from a
prefiously prepared wind row, or there may, by means of
blades attached to rotating drums, mix the material in
place on the road. The general instruction covering these

procedures are as follows: —-—

SHAPING

78

Before the roadway is sacrificed for pulverisation,
it must be brought to its final shape and crown. As a
means of checking the crown, long 2" x 8" stakes may be
set at each station four or five feet outside of each edge
of the section to be treated before construction begins.
These stakes can be graded to some elevation above the crown
grade of the completed base. After shaping is complete
a string may be stretched between the stakes and the dis-

tance from the string to the roadway measure.

When shaping Operations are completed and before
pulverizing operations begin sufficient number of density
tests in the portion of the road way to be treatedto de-
termine the depth to which it will be necessary to scarify
the grade to result in a soil-cement mixture of the required
thickness and prOportions. Tests shall be made alternate-
ly to the right of center line, and to the left of the

centerline in order to determine the average density.

The following example illustrates the procedure to
be used in calculating the depth of the material to be

pulverized under the assumed conditions given below.

0

Required density of soil-cement mixture after compaction 8
110 P.C.F.

Density of soil to be treated, after shaping is completed 8
90 P.C.F.

Cement contents by volume of compacted soil-cement mixture =

10’

Required compacted depth of base = 6 inches.

Then one sq. ft. of compacted base will contain lxlx6/12 - 0.5
cu. ft. of soil cement-mixture or 0.5 x 110 a 55 lbs. of
which 10$ by volume is cement or 0.1 x 0.5 I 0.05 cu. ft.

of cement or 0.05 x 97 = 4.7 lbs. of cement. 55.0 - 4.7

8 50.3 lbs. of soil will need to be sconified in the road-
way. Since the soil in the roadway weighs 90 pounds per
cu.ft. to obtain 50.3 lb. of soil it will be necessary to
scerify the grade to a depth 0f‘2g6§ - 0.56 ft. or 6.7 inches.

PULVERIZATION

One of the most important factors contributing to
the durability of this type of base is a uniform mixture
of soil and cement. This obviously cannot be secured un-
less the soil is properly pulveriged before the cement is
added, as very little pulverization is obtained during

soil-cement mixing Operation.

Samples for pulverization tests shall be obtained
from each type of soils in the section being processed.
These samples shall be taken entirely through the depth

of pulverized material.
CEMENT SPREADING

The plans and specifications state the cement re-

,quirements for each section of roadway in terms of cement

per square yard of roadway, or as a percent by volume of
the compacted soil-cement mixture. The quantity of cement
is usually computed by spacing bags at regular intervals
on the section of road to be treated, there emptying the

bags on the grade.

The following procedure illustrates the methods
used in calculating the preper spacing of the bags of
cement for the assumed conditions given below.

Width of road way = 24 ft.

Thickness of box 3 6 in.

Cement content by volume of compacted soil-cement
mixture I 10%

Each yard of roadway contains 3 1.3 x 6 = 4.5 cu. ft. of

soil-cement mixture.
A cement content of 10 w by volume a 0.10 x 45 - 0.45 cu.
ft. of cement per sq. yd. of base.

Each 100 ft. station or roadway contains 26 x 100 - 267
___§____

sq. yds. or each 100 sq. foot station will require
267 x 0.45 a 120 bags of cement.

If these bags are placed in 4 rows, then each row will con-
tain 30 bags. If the outside rows are set in three feet
from each edge and the inside rows and set 3 feet outside:
of centre line, then each row will cover six feet of width.

The longitudinal spacing will be 100 a 3.3 ft. between

81

bags and if the first end row of bags is placed 1.6 ft.
inside the end of the station then each cross-sectional

row will cover 3.3 ft. or length or 3.3 x 60 3 2.2 sq. yd.
"'—1F“'

or 1 : 0.65 bags / sq. yd.

MOISTURE C0NTENT4

To obtain a base that will have durability compar-
able tO the specimens that were prepared intthe laboratory,
on which the cement requirements for the project are based, it
is necessary to have an accurate control of the soil-cement
mixture prior tO compaction. The water-spreading equip-
ment must be equipped to apply a uniform volume of water
to the subgrade during the time it is in Operature. Non-
uniform water distribution will not only cause considerable
rolling and other construction difficulties but it will
also result in reduced base durability.

Samples for moisture control shall be Obtained
through the entire depth of treatment from each type of soil
after pulverization Operations are completed and Just be-
fore the cement is applied. The after dry nuxing is com-
pleted samples should be taken from the same locations as

before to determine the moisture loss during the soil-cement

nuxing Operations.

Using assumed conditions, the following example

illustrates the quantity of water to be applied to the soil-

cement mixture.

10 fi
7,6

Moisture contents of the raw pulverized soil

Moisture contents of the soil-cement mixture
Moisture loss during dry mixing I 3%
Moisture content Of mixture requiredfor compaction I 18%
Required density of the compacted material = 110 P.C.F.
Wt. of water per gallon I 8.34 lbs.

Knowing that moist mixing will require more time than dry
mixing and that it will occur in a warmer part Of the day

add one percent more than the loss during dry mixing.

Then the total moisture to be added =
18$ 9 7f +4£¢ I 15%
One sq. yd. of roadway 6 in. thick 2
h 3 x 3 x 6 = 4.5 cft.
"TE

Which will require 4.5 x 110 x 0.15 a 8.95 or 9 gls per sq. yd.
8.34

 

Composite moisture samples acrossthe roadway shall be taken
at 200 to 300 ft. intervals toward the conclusion Of moist.

mixing to check the moisture content preparatery to rolling.

COMPACTION

Adequate uniform compaction is as essential in Ob-
taining a durable product in this type of base construction

as are the Of pulverization and moisture. Unless

the same degree of compaction is Obtained during con-
struction as was Obtained in modding specimens for durability
tests in the laboratory, comparable durability of the two
products cannot be expected. Therefore, it is essential

that a sufficient number Of density tests be conducted

Just after smooth rolling is completed to assure that ade-

quate compaction is being Obtained.

Each morning, density and moisture tests shall be
made on the sections completed the previous day. A test
should be made at each station, the first determination
was the edge of the treated material, the next at the

centre line and the third at the Opposite edge.

CHAPTER IV
BITUMINOUS STABILIZATION

Liquid asphalt and tar are applied in small quanti-
ties directly to surfaces of road as dust layers, prime
coats, protective coats, surface treatment and seal coats.
These bituminous surfacings, with some exceptions, are made
usually without heating the liquid asphalt or tar beyond
a moderate temperature. This temperature characteristic
partly distinguished them from the class of pavements
built with heavier or more viscous bituminous materials
which are heated to 3500 F., during construction. These
liquid asphalts, road oils, or tar form a large group of
petroleum and tar products. Emulsified aSphalt is also

included in this group of liquid bituminous materials.
MATERIALS

The materials to which the bituminous materials com-
monly are applied or with which they are mixed are of many
types. They range from sand-clay to a clean, graded broken
stone with coarse fractions inch or larger in size. The
materials for bituminous surfacing vary greatly in charanter.
In sand—clay or top soil roads, the material is of very
fine grading. It may pass a NO. 4 sieve. In all mineral
materials the amount of 200 mesh material or that fraction
of material that will pass a No. 200 sieve and its individual

characteristics, are critical. This fraction is frequently

designated as dust, or 'minus 200'. It Often contains
colloidal material. Its importance lies in its capacity
to produce capillary action from sub-surface water, its
uncertain behavior in combination with asphalt and water,
and its enormous surface area per unit of volume. This
latter properly severely affects the amount of liquid as-
phalt or tar to be used in its presence. For asphaltic
treatment, sand-clay or stabilized soil mixtures should
be subjected to prior tests for plasticity and liquid
limit to determine their stability.

Emulsified asphalt is a particularly useful stabilizing
material for soils, due to (l) the ease with which it
mixes with all types of soils: (2) the stability that can
be obtained: (3) the water repellent characteristics of

the mixture after drying.

In order to determine the proper amount of emulsi-
fied aSphalt which should be used tO stabilize a given
soil a short procedure should be adopted by which result
can be Obtained in a few days. The stabilized soil is
moulded into briquets one inch thickaand 4 inches in dia-
meter, compressed, dried, subjected to a water-absorption
test for 24 hours, and then tested for stability. Longer
periods Of exposure to water absorption can be used in
order to Obtain additional information. This method con-
sists briefly of the following. The liquid limit of the

soil under investigation is determined and an equivalent

86

amount of water and emulsion is added with thorough mixing.
The amount of emulsion is calnulated from the percentage ‘
Of asphalt desired to be incorporated and the water is de—
termined by difference. The mixture is trowelled into
Circular wooden forms 40 inches in diameter and 1.125 inch
deep. This provides for a briquet having atthickness Of
close to 1 inch, after compaction and drying. These briquets
are allowed to cure under a moist cloth for 24 hours under
room temperature and placed in an oven at 1600 F., until
they reach constant weight. The specimens are then weighed
and placed on a blotting paper, saturated with water, for
24 hours, or longer, reweighed and the water absorbed cal-
culated. The strength Of briquet is then determined on a

compression machine.
SOIL CHARACTERISTICS

In the classificationsof soils there is a gradual
transition from the very sandy to very clayey types. Soil
constituents, defined according to particle size, general-
ly are classified into groups. These are standardized
according to A.A.S.H.0. standard tests and described in
chapter 2. A particle size analysis showing the percentage
by weight of each of the various classes of materials aids
in predicting the behavior Of a soil. Additional valuable
information can be Obtained from physical characteristics
such as the liquid limit, the plastic limit, plasticity

index and other tests. The plaSticity index is indicative

87

Of the composition of the soil, and high indices generally
indicate high clay and colloid contents. St=bilized soil
mixtures containing approximate 30 percent of material
finer than 200 mesh results from a uniform distinction of
countless small particles Of aSphalt thrLughout the soil.
These block a sufficient percentage of the interstices
between the soil particles to prevent water absorptiOn by
capillarity, and thereby preserve stability. In the more
sandy soils, stabilization is usually obtained by actual-
ly coating the aggregate particles with a continuous as-
phalt film. The type Of mixture Obtained is dependent
upon the size of soil particles and the percentage of as-

phalt incorporated in the mix.
MIXING ABILITY

An emulsified asphalt, in order to be satisfactory
for the stabilization of soils, must possess an ability
to mix with the soil and water in a manner such that the
aSphalt particles do not coagulate but remain uniformly

distributed throughout the mass in its final condition.

A soil mixing test in which the soil to be stabilized

is used, has been developed by Thurston and Weetman (1939)l

 

lThurston, R. R. and Weetman, B. 1939. New Prac-
tical Test Procedure on Emulsified Asphalt for Soil Stabiliza-
tion, Roads and Streets, 82, (3): 50.

to show more accurately the degree of stability necessary
in an emulsion to give satisfactory results. The procedure

for making a soil mixing test is as follows.

A sample of soil is screened through a 20-mesh sieve,
and 100 grams of the sieve material is weighed into a
tarred one pound can. Twenty five grams Of distilled water
are added and the mixture stirred 30 times during a half
minute period. Fifty grams Of the emulsion are then added,
and the mixture stirred 60 times during one minute. The
can is tightly covered and allowed to stand 24 hours. 100
c.c. Of water are then added and the mixture stirred 60
times during one minute. The contents of the can are
washed on to a tarred, 14 mesh screen by means of a wash
bottle, and gentle washing is continued until all big
lumps are broken up and the washings are quite clear. The
screen is placed in the can and dried to constant weight
at 300-3500 F. The grams of material (doil and aSphalt)

retained on the screen are reported as the WPercent Break".
EFFECT ON PARTICLE SIZE OF EMULSION 0N STABILIZATION

Effective soil stabilization with emulsified asphalt
is depwndent upon the introduction.ef sufficient minute particles
of asphalt to block the interstices of the soil, and it
would seem logical that, of two similar emulsions, the
one with the smaller average particle size should be more

efficient stabilizing medium. Two emulsionsl were made

89

from the same asphalt base and water phase, but on differ-
ent dispersion equipment in order to obtain different par-
ticle sizes to study this theory. The resulting emulsions
contained average particle size of 2.5 and 10.0 microns
and contained the same percentage of asphalt. It was cal-
culated that the former emulsion contained 64 times as

many particles as the other.
EFFECT OF CONSISTENCY

The incorporation of asphalt in fine particles in
the emulsified form into soils brings up the question as
to what effects its consistancy has on the final strength
of the mixture stabilized in this manner. It has been
theorized that the asphalt is not a factor affecting the
ultimate strength Of the stabilized soil, if the strength
is tested when the soil is at its Optimum moisture contents.1
In order to investigate the point, three emulsions, having
asphalt residue with consistencies of 95 float at 122 F.,
152 and 78 penetration at 77 F., were used in stabilizing
No. 3 soil to 4.0 percent bitumen content. The dried mix-
tures were subjected to water absorption tests Of 24 and
48 hours before breaking. The results of these tests showed
definitely that harder asphaltic residues resulted in in-
creased strength Of the mixture. This is true in ease of

dry specimens as well as those subjected to the one and

90

two days absorption test. It appears then, that the asphalt
actually plays an important part in strengthening the
mixtures, although excessive strength from the use of hard
asphalt may not be necessary or desirable. Adequate stabili-
ty with maximum water resistance is frequently more import—
ant. The effect Of the quantity of asphalt used on the
water absorption of mixtures has been determined. NO. 3
soil was stabilized tO contain 2.0, 6.0, and 10 percent
asphalt. Dried mixtures were left in the water absorption
box for a period of 0, 1, 4, 8 and 14 days, at which time
the amount of water absorbed and the compression strength

were determined.

These data showed that the use of a sufficient a-
mount Of bitumen to reduce the tendency of the mixture to
absorb water in service is essential. This is true even
though the use of this amount results in strength somewhat
less than the maximum obtainable since the use of insufficient
asphalt may result in a tendency for the mixture to continu-
ously absorb moisture by capillarity and, thereby, loose
stability in service. Emulsion soil mixtures must be al-
lowed tO dehydrate on the jobto such an extent that the
emulsion is completely broken and the aSphalt becomes
present as such in a sufficient quantity tO prevent further
water absorption in service. If these conditions are not

fulfilled, stabilization h s not been properly accomplished

and the results will not be permanently satisfactory.

91

PrOperly stabilized bases should possess reasonable high
compression strength, but they are only slightly resistant
to abrasion and, therefore, should be primed with a light
application of quick-breaking emulsion, or other bituminous
material, and covered with suitable waterproof wearing

surface designed for the traffic anticipated.
SURFACE TREATMENT

Surface treatment of sand-clay and stabilized-soil
roads in desirable primarily to insure a more constant
moisture content and tO provide a wearing coat that pre-
vents attrition and dust. For success, the soil fines
must have a low liquid limit and plasticity index. On
the swept surface, a prime coat of light liquid asphalt
“-9 or liquid tar is first applied at the rate of 0.15 to
0.30 gallons per sq. yard. This prime coat must be allowed
to absorb or penetrate, preferably without any traffic
and for several days. An application of about 0.20 to 0.50
gallons Of heavier bituminous material follows. It possible,
this application in turn should be followed by a coat of
coarse sand, clean chips, or screenings. The grade Of the

liquid will be governed by the grading of the cover material.

STABILIZATION

The A.R.B.A§ Committee on tar stabilized roads de-
fines soil-stabilization as the process of treating a soil,
so that it will have sufficient bearing value to withstand
designed loads when the soil in subjected to varying mois-
ture conditions. Their investigation shows that soil
group A—l to A-7 have been satisfactorily stabilized with
tar. However, most satisfactory results were obtained with
soil groups A-l to A-4. Although it is desirable in many
cases to add granular materials, the cost Of admixture Often
preclude its use. Laboratory test should be made to deter-
mine whether the soil is suitable for stabilization without
the addition of granular material. If not, or if the quantity
Of tar or asphalt for stabilization is excessive, further
tests should be made to determine whether the cost of add- I
ing granular material is justified. Sand is preferred as
a granular material, although screening are also used.

Sand has the advantage that it is usually cheaper and more

easily Obtained.

The depth of stabilized base required is generally
determined by experience. Load test to determine the re-

quired depth is Often used. The maximum depth approved

 

4American Road Builders Association. 1946. Re-
port Of Committee on Tar Stabilized Roads. Bulletin No. 104,
Washington, D. C.

93

by A.R.B.A. Committee is 8 inches, the minimum 2% inches.
The averabe depth ranges from 3 to 6 inches, with 6 inches
being the depth commonly used. Subgrade should be compact-
ed before stabilization. The moisture content and density
Of the subgrade should be determined. Low densities and
low bearing values are generally corrected by replacing

the weak areas with more suitable material or by the addi-
tion Of a blanket or lift course. The subgrade may be
dried and compacted. Preference should be shown for prim-

ing the subgrade.

It is preferable to mix the soil when the moisture
content of the soil is slightly below the Optimum. The
moisture content of the soil may be found in the field
by drying over an open fire or an oven. The density,
'however, can be Obtained by the weight volume method,
which consists Of digging a hole in the road and weighing
the material removed. The volume of the hole is determined
by filling it with Oil, sand or similar material. The weight
in pounds divided by the volume in cubic feet gives the
density, or the weight in grams divided by the volume in
c.c. gives the specific gravity which multiplied by 62.4

gives the weight per cubic foot or density.

Opinions differ as to whether tar and water should
be added on tap Of the soil when mixing with power grader,

or whether the water and tar should be applied in alter-

94

nate layers. Sheep foot rollers should be used when com-
pacting the full depth, although pneumatic rollers and
tandem rollers have also been used. The road crown deemed
satisfactory for a stabilized base varies from 0.2 to 0.5

inch per foot, the optimum being a } inch crown.
TAR SAND MIX

The suitability Of sand for mixing should be deter-
mined by means of 'Bearing value test'. Although admixtures
are not generally used for sand mix, yet the use of friable
soil is advocated for the admixture. deing in this case
is allowed when the sand contains a limited amount of mois-
ture (from 3 to 10 percent). When sand containing excess
moisture is mixed with tar, the mix looks very rich and
if spread and compacted in this condition, it is difficult
to obtain the desired initial stability. This condition
can be corrected by aerating, but ordinarily it is quicker
from a construction standpoint to aerate and dry the sand
before it is mixed, spread and compacted, The use of travell-
ing mixing plant is preferred where as stationary plants
and power graders are also employed. When mixing with power
grader, tar should be added on top of the sand and mixing
to full depth. The maximum rate of application of tar is
one half gallon per square yard. Pneumatic rollers are
usually favoured; for cpmpacting full depth sheep foot,
roller are also used and tandem rollers for finishing.

Seal coats should be applied before excess dusting takes

95

place. A rich mix cannot be sealed to soon without decreas-
ing its initial stability. However, as most tar sand mixes
should be on the lean side to Obtain reasonable initial
stability, the seal coat should be applied before excess
dusting take place. If the mix is high either in moisture
or tar content, the seal should not be applied until the

mix has been aerated and dried out.
RECOMMENDATIONS

The following are the conclusions drawn by A.R.B.A.
Committee on tar stabilization (l946)4, based on existing
information.

1. Tar sand mixes should be classified as a type Of soil
stabilization. All sands meeting the requirements of Public
Roads Administration's soil group A-3 when stabilized with
tar should be referred to as to soil stabilization.

2. Soil groups A-l to A-4 inclusive are best suited for
stabilization with tar although certain types of soils in
group A-5 having low capillary and plasticity values may

be satisfactorily stabilized.

3. Soil groups A-5 with high capillarity and plasticity
value, and group A-6 and A-7 as such are not ordinarily
suitable for stabilization with tar. Stabilization should
not be attempted unless experienced construction forces

are available and then only if sufficient granular material
is added to raise the classification of the soil to that

70

of group A—4 or better.

4. Tar stabilization with micaceons or highly organic
soils should not be attempted.

5. Soil stabilization with tar should only be used for
lease course construction. Such bases require the addition
of a light or heavy wearing surface depending on traffic

conditions.

The specifications for water proofing soil and soil
aggregate mixtures with asphaltic material prepared by the
Asphalt Institute are given below: -—-

THE ASPHALT INSTITUTE
SPECIFICATIONS FOR WATERPROOFING SOIL AND SOIL-
AGGREGATE MIXTURES WITH ASPHALTIC MATERIAL . . . . . .

PRELIMINARY INVESTIGATION
I. Soil Survey and site investigation
A. A soil survey and site investigation shall be con-
ducted of the proposed areas to be paved and ad-
jacent areas to Obtain pertinent information in:

(1) Determination of the soil profile.

(2) Selection Of suitable fill materials.

(3) Selection of soils in the area tO be paved
and adjacent areas which are suitable for
asphaltic waterproofing.

(4) Design of typical sections.

(5) Design and location of drainage.

B.

97

The soil profile and site investigation shall be

determined by exploratory sampling, testing of

samples and complete interpretation of laboratory

test data.

(1)

(2)

Preliminary sampling shall be made by borings
at intervals not to exceed 200 feet. Borings
shall be made closer than 200 feet where
variable soil conditions are encountered.
Depth of borings shall be controlled by the

topography and surface conditions. In cut

‘sections, borings shall be carried to 6 feet

below finished grade. In areas where little
grading will be required, borings shall be
carried 6 feet below the natural ground line.
If free water or seepage is found, borings
shall extend down through the water bearing
layer, or to a depth Of 10 feet. Ground water
elevation shall be located, if conditions

are such that stability Of subgrade will be
influenced by it. In borrow pit areas, trial
borings shall be made in cross section pat-
tern tO determine quality of soil within
reasonable haul distances.

Samples representative of the natural soil
strata as they occur on the project shall

be taken for complete laboratory analysis

98

of existing field density and moisture conditions, suitabili-
ty for subgrade material, and suitability for use in soil
asphaltic waterproofing.

(3) The results of soil sampling and laboratory
tests shall be plotted to scale in preparing the soil

profile map.

II. Laboratory studies
A. Soils prOposed to be employed in construction
under this specification shall be tested in accordance
with the Texas Highway Department Standard MOdified Bearing
Value Test TED-98.
B. That portion of the soil passing size 40 mesh
shall have a plasticity index Of not more than 12, A.A.S.H.O.
Std. Test, or not more than 15 On slaked samples.
0. Soils failing to meet the requirements of Sections
"A'' and "B" may be used provided they are first mixed
with other mineral products to produce a mixture which:
(1) Is satisfactorily waterproofed after treat-
ment with asphaltic materials.
(2) Shows a stability after seven days capillarity
in excess of 400 pounds.

(3) Does not crack upon dehydration at 140° F.
DESIGN

1. Subgrade
A. Fills shall be constructed in layers not exceeding

99

6 inches before compaction and shall be compacted to at
least 95 percent of the maximum density at Optimum moisture
as determined by the Standard A.A.S.H.O. Method. The top
12 inches Of all areas over which pavement is to be placed,
plus 3 feet on each side, which are either cut areas or
undisturbed areas, shall be compacted to a density Of

at least 95 percent of the maximum density obtained by
compacting samples at Optimum moisture ad determined by

the Standard A.A.S.H.O. Method.

B. The completed subgrade shall be maintained in a
condition equal to that specified under sub-paragraph A.
After rains the subgrade shall be allowed to partially
dry out and shall be recompacted to the density required
under sub-paragraph A. Adequate drainage by means Of bleed-
er ditches shall be provided for all areas which are subject

to ponding of water after rains.

II. Drainage

Drainage shall be designed to successfully intercept ,
and remove surface run-Off and underground water flowing
toward the paved area from lands outside Of and adjacent
to the paved area; and collect and remove surface run-Off
from the paved area; and collect and remove excess under-

ground water from the paved area.

III. Thickness requirements
to Wheel load BXPGCtede

100

B. Nature of the subgrade.

C. Economics.

A wheel load of 10,000 to 12,000 pounds is usually
the maximum requirement for highways. In airport work,
wheel-loads have already reached as high as 75,000 pounds

and will probably go higher.

The Public Roads Administration has a method of
design based upon principles long used in highway con-
struction. These depend upon a classification Of soil
from A-l through A-7, and they recommend varying inches
Of thickness of pavement depending upon the type of soil

and the wheel load as shown in Table I.

 

 

TABLE 1.
Wheel Load

Class Of Soil , , , ,

pounds pounds pounds pounds

Inches Inches Inches Inches
Arl 0-6 3-6 3—9 4-12
A-2 Friable 0-6 3-6 3-9 4-12
A-2 Plastic 2-8 4-10 6-12 8-15
A-3 4-6 5-8 6-9 8-12
A-4 9-18 15-25 18-30 24-36
A45 9-24 15-30 18—36 24-48
A96 12-24 18-30 '24-36 30-54
A-7 12-24 18-30 24-36 30-54

 

101

In the preliminary investigation including a soil
survey, site investigation and laboratory studies as is
covered in detail above, you will nO doubt use one of the
four plans of analysis, so that determination of thickness
of the treatment will depend upon information that you
have available in your soil survey, plus load and traffic
expected on the type of road to be designed, as well as

funds available for its construction.

In most highway work you are concerned with wheel
loads of 10,000 pounds or less, thus in accordance with
Table I, pavement thickness would be from zero to 8"
in thickness for all soils up to an A-4, with an A-4 re-
quiring 9" to 18". In the following discussion, it is
shown that a soil having PRA rating of more than A—4 is

considered impractical.

IV. Selection and Admixtures of Soil and Soil Aggregates
The soil survey and studies made in the preliminary
investigation under this procedure give the engineer a thor-
ough picture Of the soil conditions on a given construction
project. If the soil on the site has a classification Of
PRA A-4, A-5, A-6 or A-7, it will without a doubt require

some admixture Of a more granular type of soil or soil
aggregate before it will be practical tO waterproof with
aSphaltic material. In the selection Of the correct ad-

mixture Of soil and soil aggregates, one must consider not

102

only the tests on the various materials available, but

also the length of haul on each aggregate to place it at

' the job site, as well as the cost Of asphalt. We recommend
that when several choices of materials are available at

the same cost that the mixture be used that requires the
minimum amount of asphalt. Where a percentage of asphalt
above 12% is required to waterproof a soil, the project is
of doubtful practicability and the addition of granular

materials is recommended.

Concerning the suitability of a soil for this type

of construction, as a general rule, whenever there is a
question as to the fineness to which the soil should be
broken down before the mixing of asphalt, such soil is
not desirable material for soil and soil aggregate asphaltic
waterproofing. If it is used, it will require dilution
with granular material to an extent that will ordinarily
eliminate the question of fineness of breakdown. The type
of mixing equipment available and the efficiency of this
equipment will also govern the selection of aggregate.
For instance, most types of mixers will take lumps 6" in
diameter or larger, and at the completion Of the mixing
procedure such 1 mps will be ground to i“ or less. With
such equipment, any regulations as to the fineness Of the
soil before mixing is obviously superfluous.
VJ Type and quantity of asphaltic waterproofing agent

A. The asphaltic water roofing agent employed shall

103

be the type as specified in the plans and shall meet The
Asphalt Institute requirements for asphaltic cutbacks,
asphaltic emulsions, or aSphaltic cements. The type of
mixing employed may determine the type of asphalt used,
but all factors being equal the product containing the
highest percentage residual asphalt would be most economi-

cal.

B. The maximum quantity of asphaltic waterproofing

agent employed shall be based on preliminary laboratory testsl

C. The maximum quantity of asphaltic waterproofing
agent employed shall be one (1.0) percent below the amount

predetermined as the "fat point" of the soil.
CONSTRUCTION PROCEDURE

1. Description, General

A uniform mixture of soil and soil aggregate type
asphaltic material shall be laid to a finished thickness
of --- inches in compacted and cured layers, not exceeding

two inch maximum thickness.
11. Materials

A. Soil and aggregate material shall consist of the
various selected soils, soil aggregates and admixtures

as determined in the Design section of this procedure.

B. The asphaltic waterproofing material shall consitt

104

of cutback aSphalt, emulsified asphalt or asphalt cement,

as determined in the Design section of this procedure.

III. Construction
A. Material shall be placed as required for treat-

ment with the equipment available.

B. Asphalt per cent shall be determined in Design,
control of which shall be specified by Procedure for Con-
trol below. Water used shall be the minimum required for

efficient mixing.

IV. Control of Construction Mixes

Laboratory studies and determination of per cent as-
phalt required shall be correlated with soil and soil
aggregate gradation and soil and soil aggregate plasticity
index, and a chart prepared for the use of the engineer
in controlling mixtures in the field. Where there is a
question of the actual per cent of asphalt added by mechani-
cal device measurements, a check Of the asphalt content

shall be made by Soxhlet or Rotorax extraction.
CURING, BEFORE AND AFTER COMPACTION

The most important phase of successful construction
through the use of soil and soil aggregate asphaltic water-
proofed mixtures is the curing. The mixed material shall
be bladed to one edge of the base area and allowed to aerate

and cure. When cured to the extent that a one-inch layer

105

can be compacted by a pneumatic roller, such spreading Opera-
tion shall be accomplished as part Of the operation of
moving windrow to the Opposite side Of the road. In the

case of tracking of the pneumatic roller due to wet Spots,
such tracking shall be removed and smoothed by blading and
again compacted. This compacted layer shall be allowed

to cure until the moisture content is not over 1% times

the moisture content of the lavoratory specimen cured in

the 140° F. oven referred to under Laboratory Studies, above.

When first layer is cured as above, successive layers
shall be spread and compacted in‘a similar methed with

similar control.

The finished base shall be tested by Texas Highway
Department THD-90 Rubber Ballon Method, and show a density
of at least 95 per cent Of the density of the laboratory

specimens.

If the asphaltic mixture is of a rich design, it
may be expected to withsaand light traffic without injury
to surface and with beneficial compaction to the base.
If, on the other hand, the design is on the lean side of
asphalt content, traffic should not be permitted until

after surface treatment.

.LUO

CHAPTER V
CHEMICALLY STABILIZED ROADS

The use of chemicals to stabilize road mixtures
has gained great pOpularity during recent years. Thenead—
mixtures are normally used with soil aggregate gradations
having mechanical stability, where in they serve to increase
the density Of the compacted mass and minimise daily and
seasonal fluctuations in moisture content. The most common-
ly used chemicals are delinquescent salts, like calcium
chloride and sodium chloride. These salts help to retain
moisture in road surface, thereby preventing the disinte-
gration Of fine particles. Such materials have, therefore,
no advantage in humid areas and their primary use is in
dry climates. In very dry and arid regions, where there
is very little water in the first instance, they have-
no advantage, as a certain minimum of moisture in the at-
mosphere is necessary for the salts to be effective. This
chapter deals mainly with calcium chloride which has now
been used as a treatment of unpaved road surfaces for more
than 25 years. It is a fairly common practice now-a-days
to spread calcium chloride over the road as a means Of
preventing dust and providing greater strength and durability

to the road surface.
FUNCTIONS OF CALCIUM CHLORIDE

Calcium chloride is a white highly delinquescent

107

salt. It does not occur naturally except in solution in
salt brines and mineral springs, and as a constituent in
a few minerals. The most important sources are natural

brines and by—products produced in the manufacture of am-
onia and amonium carbonate by the Solvay Process. It is
interesting to note that the chemical was considered a

waste product and difficult to dispose of until research

and develOpment led to its use in several varied fields.

Calcium chloride is delinquescent and hygroscOpic.
Delinquescence is the ability Of the material to absorb
moisture from the air and thus to be dissolved and became
liquid. Hygroscopicity is the ability to abosrb and retain
moisture without necessarily becoming liq id. Calcium '
chloride possess these two characteristics to a marked

degree as shown in the table below.1

Delinquescence.
(deest Relative Humidity and Temperature at which Calcium
Chloride will Dissolve).

Relative Humidity 20 30 4O 43
Temperature deg. F. 100 74 44 42
Hygroscopicity.

(Pounds of water taken up by one pound of flake calcium
chloride at different humidity.)

 

lCuthbert, F. L. 1945, Use of Calcium Chloride in Granu-
lar Stabilization of Roads: 3. Highway Research Board, Washing-
ton, D. c.

108

Relative Humidity 36 60 70 80 85 90 96
Temperature deg. F. 77 77 77 77 77 77 77
Pounds of water taken

up by 1 lb. of CaClz 1.0 1.6 2.0 2.8 3.5 5.0 8.4
The extent to which the chemical exhibits these properties
under natural condition is governed by temperature and
humidity in such a manner that the higher the relative humidi-
ty of the air the more will be absorbed at a constant
temperature; and the higher the humidity, the lower the

temperature at which the chemical will dissolve.

Vapour pressure is a direct measure of the speed
of evaporation and is directly affected by temperature and
the strength or concentration of the material. While cal—
cium chloride itself does not evaporate, the water in a
solution containing calcium chloride will, although at a
slower rate than pure water. This means that soils con-
taining calcium chloride in solution will remain moist

longer than if the calcium chloride was not present.

Surface tension in also related to the rate Of evapor-
ation in such a manner that a solution possessing high sur-
face te sion will tend to evaporhze less rapidly than one
having low surface tension, with other factors constant.
Calcium chloride increases the surface tension of water.

A 25 percent solution of calcium chloride increase the sur-

face tension Of water to about 14.6 percent higher than

109

that of pure water. If dry soil is mixed with water to

any fixed percentage Of moisture, that water will proceed

to evaporate until the soil in again as dry as it was before;
but if mixed with an equal quantity of calcium chloride
solution which is in equilibrium as to temperature and
relative humidity, it will stay continuously as moist as

the calcium chloride solution will render that soil.

Water plays a prominent role in stabilization,
first it is necessary to make the clay cohesive, and second,
it provides the medium by which maximum density can be Ob-
tained by compaction. Practically all of the water added
to a clay, silt, sand and gravel mixture will be preferential-
ly absorbed by the clay fraction. It is also known that
the clays are made up for the most part Of very small plate-
like minerals, called clay minerals, andthat these minerals
have peculiar water absorbent prOperties. {Due to the
electrochemical activity of the clay-minerals; water is
absorbed in such a fashion that it actually exists in dif-
ferent forms, from the surface Of the clay mineral particle
outward through the thickness of the water film. The mole-
cular layer of water close to the surface of the particle
is absorbed so strongly that it is more like solid than
liquid water. As the water layer or film thickens this
solid character is lost due to the decreased strength,
as the distance from the clay-mineral particles increases.

Consequnetly, theouter layers are more like the water we

110

commonly think of. The property or the ability of the clay
to absorb water may vary considerably with the clay due
to the fact that it may be composed Of different types of

clay-minerals.

These moisture films must play a part in compaction
and may be critical from the standpoint Of obtaining and

2 measure the ability

maintaining stability. Proctor tests
of clay to absorb moisture. MOisture density curves, as
determined by Proctor method show that maximum density is
obtained over a relatively narrow range of moisture content
with soils containing small percentage Of clay and that
with either greater or lesser amounts Of water the density
decreases, when the compactive effort is kept the same.
This narrow moisture range is further indication of the
importance Of moisture control in stabilization and of the
possibility of Obtaining improvement through the manipula-
tion Of the clay-water relationship either by chemical or

physical methods or combination Of both.

Calcium chloride when used in granular stabilization,
due to its hygroscOpic and delinquescent prOperties will
attract moisture and dissolve so that a calcium chloride

solution if formed. Therefore, when this chemical is used

 

aProctor, R. R. 1933. Fundamental Principles of
Soil Compaction. Engineering News Record, 3, (No. 9, 10,
11, 12, 13).

i“

we no longer have a clay-water relationship to consider
but a clay-calcium chloride solution relationship and the
problem is to determine how these two relationships differ.
In order for a calcium chloride solution to have any effect
on stabilization it is necessary for it to move throughout
the material being treated and stabilized. The efficiency
of the movements of czlcium chloride solution depends upon;
evaporation, soil texture, percolating water, soil cover,
and temperature. Slesset (1943)3 found that the calcium
chloride solution migrated downward by leaching from the
surface and that under conditions of evaporation it was

not found on the surface but it did have a tendency to be
concentrated in the upper layers, so that any beneficial
effect which might occur from it presence would be repititious.
Since the chemical did not crystallige on the surface dur-
ing evaporation very little was lost by run-off. The per-
manence of the calcium chloride solution was found to be
directly affected by the type of soil; a sandy-clay soil
apparently holding the chemical better than others. Proctor
(1933)2 finally concluded that the chemical should be

mixed integrally with the soil for best results.

The aims Of stabilization are to make the soil as

 

BSlesser, C. 1943. Movement Of Calcium Chloride.
Proceedings Highway Research Board, 23.

2Proctor, R. R. 1933. Fundamental Principles Of
Soil Compaction. Engineering News Record 3, (N5. 12, 13)

112

dense as possible and to prevent the thickness of the
moisture films from Changing. Stabilization hinges on

the bonding action of these films. Calcium chloride op—
erates to conserve water in soil by reducing the rate Of
evaporation in dry spells and by absorbing water from the
atmosphere under conditions Of high humidity. MOisture
film cohesion furnished by calcium chloride is greater and
last longer than that furnished by water alone. This fact
is of great importance in promoting stability since one

Of the main requisite of stabilization is not only to sup—
ply the correct amount Of water during construction so that

maximum density can be attained by compaction but also to

maintain the proper moisture film to insure stability.

Hogentogler and Willis (1936)4 state that treatment
with calcium chloride or sodium chloride effect a decrease
in the volume and an increase in the density and stability
Of graded road mixtures; the calcium chloride does this
through eloctrolytic and crystalline properties. Be-
cause solution of calcium chloride and sodium chloride
have lower vapour pressure than water, the evaporation Of
moisture from soil mixtures wetted with the salt solution

is definitely slower than similar mixtures moistened with

 

4Hogentogler,.c. A. and Willis, 0. A. 1936. Stabiliz-
ed Soil Roads. Public Roads, 11, (3).

.LAO

water. These salts in a stabilized road, therefore, tend .

to conserve its moisture.

Hogentogler (1928)5 illustrated the effect of cal-
cium chloride on density by using the same compactive ef-
fort (135 lbs. per sq. m.) on a treated and on untreated
soil. The untreated soil had an Optimum moisture content
of 41.2 percent compared to 33 percent for the same soil
treated withccalcium chloride. Also to have the same mois-
ture content of 33 percent, the untreated soil required
a pressure Of 1,100 lbs. per sq. m., where as the treated

soil required only 135 lbs. per sq. in.

The following are the effects which have been ob-,
tained in the field by the use Of calcium chloride in stabiliz-
ed mixture, under favourable condition: ---

l. The general behavior Of roads with calcium chloride
admixture is superior to those with no calcium chloride
added.

2. Calcium chloride expedites compaction in roads in
which it is incorporated.

3. The binding of aggregate, securely in place, with

stable soil mixtures and calcium chloride, eliminates

 

5Hogentogler, c. A. and others. 1938. Use of
calcium chloride in Road Stabilization. Calcium Chloride
Association. Washington, D. C.

114

most of the destruction and loss of road material due to
the action of traffic. '
4. The use of calcium chloride results in a firm, bound

and dustless surfaces.
SPECIFICATIONS FOR DISIGN 0F HIXTURES

For most practical purposes, only two soil tests
are absolutely essential to control stabilized mixtures.
1. Mechanical analysis will furnish adequate data for
the design of aggregate surface courses which will readily
compact, and attain high density and stability.

2. The plasticity index will furnish design data for ob-
taining maximum resistance to abrasion with effective

capillary characteristics.

The coarse limit of grading is approached in lpase
course which are covered by bituminous mats. Conversely
the fine limit Of grading is approached in wearing courses
requiring the use Of calcium chloride as a stabilizer. The
plasticity index of the range of material passing the NO. 40
sieve is held high to insure adequate resistance to traffic
abrasion, without excessive slipperiness, and maximum re-
tention Of calcium chloride in the capillary water of the
road surface during the wet weather cycle. In case where
the use of calcium chloride is not feasible due to low
traffic density, it is desirable tO carry maximum soil

fines and a higher P.I. range to secure satisfactory results.

L.Li.)

The extra soil fines are necessary to compensate for the

loss of fines during wet weather.
CONSTRUCTION

Calcium chloride stabilized roads are classified
into, (1) Surface consolidation, and (2) stabilization.
Surface consolidation means improving the surface of a
road as a maintenance function, by utilizing shoulders or
easily Obtained soil material for the purpose Of building
up, consolidating and smoothing the resultant surface,
with the aid of moisture and compaction, in order that the
calcium chloride treatments will function longer and more

effectively.

Stabilization includes the construction Of a dense
wearing course or kpase composed of a designed and control-
led mixture of graded aggregate, binder soil, and calcium

chloride used either integrally or on the surface or both.
SURFACE CONSOLIDATION

An untreated gravel or crushed stone surface road
becomes dusty in dry weather, and developes an appreciable
amount Of loose aggregate. It has been common practice
to windrow this loose stone to the side of the road, to
be bladed back again during wet weather. While this prac-‘

tice is admittedly better than the 'mulch' method Of leav-

116

ing loose material under the wheels Of traffic, it is il-
logical, in that the windrowed material is giving no ser-
vice tO traffic but on the contrary constitutes a hazard
to emergency use of the shoulder and obstructs the flow

of storm water.

The consolidation of loose aggregate on road surface
is a maintenance Operation and may be accomplished satis-
factorily by the SO called 'trial and error' method. This
consists of mixing a trial amount of pulverized clay or
clay combination soil with loose aggregate. The trial
amount is usually about 10 percent Of the volume to be
consolidated. Water is added and the mixture is shaped
and compacted under traffic. The dry mixture may be
windrowed to be bladed into the road during the next rain.
If the local soil from the shoulder is of a cohesive nature,
it is frequently used and bladed in the loose aggregate
as building material. The preservation of the moisture
in the mixture is very essential and may be accomplished
by surface application of calcium chloride. If the road
surface shows a tendency to muddiness in wet weather, an
excess Of binder soil is indicated, and this is corrected
by a light application of coarse sand, fine gravel, crushed
stone or slag. The behavior of road under traffic in both
wet and dry method this becomes the practical means Of

establishing a balance between aggregate and binder soil.

117

In this type of construction, a rough method of
testing materials without laboratory equipment is suggested
by Hogentogler and Willis (1936)4. A sample of well-graded
sand and binder soil may assist in the selection of soil
mixtures that have the desired properties. If a sample
of well graded material is wetted and squeezed in the hand,
the folhowing characteristics will be noted, (1) the soil
is extremely gritty, (2) it can be formed into a definite
shape that retains form even when dried, (3) when in the
palm of the hand it will compact into a dense cake that
cannot be penetrated readily with a blunt stick the size
Of a lead pencil. Development of some strength on drying
indicates a sufficient amount of binder soil. Resistance
to the penetration of the pencil or stick even when the
sample is thoroughly wetted, indicates a desirable inter-
locking of the grains and the presence of a sufficient '
amount of capillary force. Too much sand would cause the
sample to fall apart when dried. Too much clay would
leave the hand muddy after the wet sample was squeezed and
would cause the wet sample after being petted, to offer

little resistance to the penetration Of the stick.

The method used when a road is to be consolidated

 

4Hogentog1er, c. A. and Willis, C. A. 1936. Stabilized
Soil Roads. Public Roads, 11, (3).

is as follows. An examination of the whole road is made

to locate weak spots because it is seldom that a road is
uniform over its whole length. Where there are evidences
of soft Spots in wet weather, stone is added. Where should—
ers do not contain binder soil this is imported. In ex-
treme cases this binder soil should be mixed to sufficient
depth to support the traffic, then the maintainer is put

on the road. The outer end of the blade is Set well down
and forward to cut in binder soil. It will generally be
found that this material contains much gravel as well as
binder. The blade should be set so as to produce the maxi-

mum rolling effect in order to improve the mixing.
STABILIZATION

Briggs (1938)6 conducted experiments in Nebraska

on a number Of projects with the following results: ---

In hot dry weather considerable difficulty was
experienced in Nebraska in laying clay-gravel stabilized
soil mixtures, because the consistency of the mixture changed
rapidly as a result of evaporation of the water during the .
manipulation process. Retarding this evaporation was con-
sidered one possibility for making the stabilized base

course easier to lay, thus permitting smoother riding sur-

 

°Briggs, C. F. and others. 1938. Use Of calcium
in Road Stabilization. Proceedings Highway Research Board,
lg, (Part II)e

119

face to be attained.

The theoretical water required was determined by
proctor compaction test for minimum density for each of
the mixtures. It was thought that a substantial portion
of the cost of the calcium chloride might be offset by
the saving in the water used. The calcium chloride was
applied with a drill type spreader. As soon as the mater-
ials making up the graded mixture were partially dry mixed,
approximately 1/3 of the windrow was spread nine or ten
feet wide on the road-bed. One third Of the total applica-
tion Of the chemical was added to this material. This pro-
dedure was repeated until the required quantity of calcium
chloride had been applied. Dry mixing of the materials
was then resumed and continued until uniform mixture was
obt ined. The total quantity Of calcium chloride was a lb.
per sq. yd. per in. of depth of the local base. In these
projects the chemical did assist materially ingthe construc-
tion operations. It was easier to Obtain uniform distri-
bution Of moisture throughout the stabilized soil mixture
than it was on others on which the chemical was not used.
By retarding evaporation during the operation of spreading
and compacting the mixture, it was possible to Obtain
smoother riding surfaces than in usually the case with

this type of construction.

ROAD Mixing: --- Road mixing means the mechanical mixing

Of the various constituents directly on the subgrade or

road lease, as contrasted with material mixed in plants.

If the binder soil is being Obtained from the roadway,
shoulders, or slopes, or from a shallow pit Of consider—
able area, it is advantageous to remove the soil by blad-
ing it off in thin cuttings, which pulverize easily when
dried. All of the binder soil should pass one inch sieve
and at least 80 percent should pass a N8. 4 sieve. Enough
of the graded aggregate and binder soil to give the desired
depth of compacted wearing course, shOuld be thoroughly
mixed, by alternately spreading and windrowing the materials,
or by multiple blade maintainer, or by other suitable methods.
This mixture should then be bladed into a uniform windrow

on each shoulder of the road to be redistributed as Speci-
fied. In blade mixing the various ingredients composing

of stabilized wearing course, it is highly important that

no appreciable amount of extra soil be picked up from the
subgrade or shoulders. The blading of wearing course to

a smooth finish formation requires that some thin cuttings
be made, often resulting in seggregation of coarse aggregate.
To avoid leaving loose stone on the surface, it is advisable
to start the finish blading on one side of the road and
carry it across the road, by successive trips, leaving any
accumulative loose stone on the Opposite shoulder. Proper

moisture content is essential in this Operation.

\

WATER Application: --- The construction of stabilized courses

121

by road-mix method during periods Of prolonged dry weather
may add unduly to the cost Of the work by reason Of the
amount of water required to provide the Optimum moisture
content. The cost may be greatly reduced, where traffic
conditions permit, by dry mixing the aggregate, binder

soil, and flake calcium chloride, and windrowing the mix-
ture to the side Of the road, awaiting a rain before spread-

ing.

ROLLing: --- The stabilized mixture should be thoroughly
compacted, at the optimum moisture content, to develop
density. In some localities where the traffic is heavy

and well distributed over the width of the road, compaction
may be secured without rolling. In other localities where
rolling is necessary, the truck wheel type of roller is
preferable to the solid type, because it compacts the mix-
ture from the bottom upward, with an effective kneading

action.

PLANT Mixing: --- Plant mix include either a central mix-
ing plant or a portable plant, Operating along the road.
The advantages of plant mixing over road mixing are as
follows: ---

1. A more uniform mixture is obtained.

2. Less delay on account Of unfavorable weather condition.
3. Less interruption of traffic.

4. Greater convenience and less cost of applying the ne-

122

cessary water for the mixture.

5. Less equipment required on the road.

6. Greater ease of laboratory control of mixtures.

7. Possible utilization of soil strippings which are other-
wise wasted.

8. Utilization Of fine aggregates, or certain size of
coarse aggregates, which may have accumulated in the prO-

duction Of materials for other purposes.

The Operation consists essentially Of pulverizing
the binder soil, prOportioning, and feeding the graded
aggregate, binder-soil, calcium chloride and water into
a mixtr, where they are combined uniformly and delivered
into trucks or storage bins. In the process most commonly
used, the binder soil is dumped into a hopper from which
it feeds by gravity to a Screw-conveyor which delivers it
at a uniform rate to a disintegrator, either directly or
by means of an intermediate belt conveyor. The disintegrat-
or unite consists of two pairs having one large-diameter
smooth-faced roll Operated at low speed and one smaller
diameter roll with longitudinal knives set in its face,.
Operated at igh speed. The lower pair, or crusher-rolls
are both of the same diamether and are smooth faced. Graded
aggregate and flake calcium chloride are delivered from
Storage happers by controlled feeds along with the pulver-

ized binding soil into a mixer, usually a pug-mill type.

A pipe line provides the water necessary to bring the mois-
ture content of the mixture up to 5 to 8 percent. The
pug-mill contains longitudinal shaft to which replaceable
blades are attached as such angle as to mix the materials
continuously and convey them through the mill to an out-
let, where the finished mixture is taken by belt or bucket
conveyor to storage bins 1 or dropped into a pit from which

it is loaded by clam shell into trucks.
MIXING CALCIUM CHLORIDE

If the stabilizing is being done by the'mixed in place'
method the desired prOportion Of flake calcium chloride
is added to the combined aggregate in windrow on the road
and thoroughly mixed dry by blading the aggregate across
the road surface until the chloride is evenly incorporated.
The road surface is then moistened until enough water has
been added to the aggregate to Obtain the necessary workabili-
ty. The whole in then laid into the roadway, and bladed
and rolled, until a smooth even riding surface is obtained
and compaction is well into its final stage. Generally
traffic completes the compaction. In the plant mix as in
the mixed in place method flake calcium chloride and water(
in the desired quntities are added to the combined aggregate.
The whole is then mixed -ntil the chloride is thoroughly
and evenly incorporated and a state of workability is at-

tained. For surface treatment it is economical to apply

flake calcium chloride, in conjunction with the use of water

tanks, and then only to thoroughly clean surfaces.

Burggraf (1938)6 suggests the following procedure
prior to the mixing Operation, when calcium chloride is
used as an admixture in the road mixed material. The
graded aggregate and binder soil should be loosely spread,
individually or in combination, over the prepared lease.
Flake calcium chloride should then be spread uniformly
over these materials at the rate Of 0.5 lbs. per sq. yd.
per inch of thickness. In no case should the amount Of
calcium chloride exceed 2 lb. per sq. yd., which limits
the maximum thickness to be treated to 4 inches. If a
compacted stabilized wearing course of greater thickness
than 4 inches is specified, the calcium chloride should
be incorporated only in the upper layer. In plant mix
theuupper material should contain 5 to 8 percent by weight
of moisture and at least 10 lb. of calcium chloride per
ton of mixture. After being maintained for five to ten
days the compacted road should be given a surface applica-
tion of calcium chloride Of at least 0.6 lbs. per sq. yd.
If calcium chloride was not used as an admixture, the road

after its initial compaction and shaping should be given

 

6Burggraf, F. 1938. Use of Calcium Chloride in Road
Stabilization. Proceedings Highway Research Board, 18,
Part II.

a surface application of calcium chloride of 1.0 lbs. to
1.5 lbs. per sq. yd. In either case the surface applica-
tion of calcium chloride should be made during periods of
high humidity, as during the night or early morning hours,
or when the surface is in a damp condition from sprinkling

or from natural casuses.
CROWN

A section having a good surface should have a
crown of 0.5 inch per foot of width. The most Suitable
type is of straight lines dropping both ways from the cen-
ter. A modified type which has practically an even cross-
fall to either side, with the center slightly rounded would
be practical. The magnitude Of crown is not so important
on stabilized roads on grades as on level section. If
the surface of the road is rolling it naturally drains
well, but if it is level the cross-slope must be adequate
or the sluggish drainage will cause surface defects. Due
to the hard and compacted surfaces of stabilized roads,
they do not sour easily, so are capable of carrying the
longitudinal flow of storm water for short distances, down

the grade before discharging it into ditches.

For the determination of the crown height the follow-

ing formula is recommendedbby Burggraf (1935)7

 

7Burggraf, F. 1935. Importance of Crown on Calcium
Chloride Stabilized Roads. Calcium Chloride Association, Bull-

etin No. 23, Washington, D. C.

C : leOO-4L)
4800

Where C - crown in niches

W Total width of road in inches.

L Longitudinal gradient in percent..

This formula gives a crown of a inch per lin. ft. on level

sections and 0.4 inch per lin. ft. on a 5 percent grade.

A checking template should be used to obtain the
required amount of crown during the construction of stabiliz-
ed roads. This template can be easily and economically
constructed, and will be invaluable in obtaining the desired
crown. The template can also be used for a rough check
of the subgrade or base, which should confirm to a shape

similar to that of the finished stabilized wearing surface.

FACTORS Affecting Construction Cost: --- The main factors
affecting the construction cost are: (1) delivered fine
and coarse aggregates, (2) prepared binder soil (3) water
applied, (4) mixing (5) spreading, (6) compaction and (7)
calcium chloride. The cost of delivered aggregate is by
far the greatest item. This item also is the cause of the
wide variations in construction price as the use of local
aggregates involving on rail haul effects a great saving

compared tO materials shipped by rail.

IAINTENAINE

All types of road surfaces require maintenance to

combat the destructive action of traffic and weathering.
Prompt action is the keynote of every good maintenance
organisation, not only to give immediate service to traffic
but to prevent further extensive and costly damage. The
stabilized surface due to its dense, well bounded structure,
necessitates a somewhat different plan of maintenance than
the loosely bound surface. Less frequent blading is required,
but it is even more important that it be done at the right
time. The maintenance objective on stabilized roads are:
(a) to provide smoothness, (b) to keep the metal compacted
without dust, and (c) to preserve the crown and thickness.

The responsibility of maintaining stabilized surfaces rests

in the hands of the man in the field.

BLADing: --- The stabilized road require much less blading
than one which normally carries a loose mulch or floating
cover. It is important that no blading be attempted un-
less the surface condition justifies it. Small holes or
corrugations should be removed by blading only during and
after rains have made the surface workable. The advantages
of blading when the road has been thoroughly wetted are:
(a) easier workability, (b) minimum disturbance and dissipa-
tion of calcium chloride which has been driven deeper into
the roads by rains and (c) presence of enough moisture to
permit consolidation of re-shaped loose material under
traffic. In prolonged dry weather where water is easily

available it is advantageous to sprinkle sections of a

stabilized surface in order to permit effective blading

to restore smoothness. During dry weather, stabilized
su4faces should be kept free from loose floating aggregate
in erder toaavoid abrasion under the wheels of vehicles.
During wet weather, it is sometimes desirable to blade in
loosened aggregate from the soil in order to consolidate
it into the surface. Excess unbound material should be
removed. During periods of heavy rain some of the binder
soil is likely to be washed to the shoulders of the road,
thereby, permitting development of_a slightly loose condi-
tion of the surface. Consequently, when blading loosened
aggregate from the edges into the road surface, a small
amount of soil from the shoulders may be brought in at

the same time to add binder, provided thesshouldered material
contains suitable clay, loam or any cohesive soil. In
case the shoulder soil is unsuitable for binder,‘a satis-
factory clay should be distributed in a small windrow on
the shoulder, where it may be dried, pulveri7ed, and held

available for use at the proper time.

APPLICATION 0f Calcium Chloride: —-- The minimum maintenance
treatment should be 1 lb. per sq. yd. and if traffic is

more this should be increased to 2 lbs. per sq. yd. Sever-
al applications should be mzde during the year. A convenient
method of application is with a box spreader suspended

from tae back of a truck. This box has notagitator but

the vibrations of the truck keeps a good flow of flake.

.LCV

About 2 lb. of calcium chloride per sq. yd. per year
are required. It would be advisable to apply in one lb.
quantities early inflanch and in September, when the moisture
from the winter and summer rains is still in the road. After
a road has been maintained for a year or so with calcium
chloride, in many cases the total yearly amount required
will drop to 1% lb. or even as low as 1 lb. per sq. yd.

The best time for calcium chloride application is follow-
ing a rain and after necessary blading or patching opera-

tions are completed.

PATCHing: --- Blading only after rains is usually sufficient
to preserve smooth riding qualities, but in prolonged dry
period it is sometimes desirable to eliminate scattered

pits which may develop by hand patching. A good-mixture

for such work consists of graded aggregate under % inch

in size, mixed with at least an equal weight of sutiable
sand-clay, water to the extent of 6 to 10 percent, and cal-
cium chloride at the rate of 100 to 150 lbs. per cubic

yard.

CHAPTER VI
UNTREATED SURFACES
EARTH, SAND, CLAY, GRAVEL, AND STONE ROADS

According to the latest‘figures available the aggre-
gate length of all public roads in Pakistan is roughly
57,969 miles, 49,398 miles or 88% of these being earth
roads. It is eveident that the construction and mainten-
ance of earth roads is of considerable importance in con-
nection with plans of public road improvement. Further
as sand, clay and gravel surfaces often constitute the first
step from earth roads to improved surfaces, these may be
expected to constitute no small part of the total mileage
in future road expansion programmes. On account of this
wide distribution information concerning their construction

and maintenance is detailed.
SURVEY

A careful survey of the following should be conducted
to determine accurately (l) the topography or lay of the
land so that the location may follow the route which pre-
sents the fewest obstacles, (2) to fit the grade line to
the ground surface so as to keep down the amount of grad-
ing necessary, (3) to balance cuts and fills so that what-
ever grading is done will be to the best possible advantage,
(4) to obtain data from which proper plans may be prepared

and an estimate of cost made, (5) to line up the road and

provide stakes for controlling the work, (6) to provide
a record that will prevent subsequent contentions among

landpowners regarding the original location of the road.

DRAINage: --- Effective drainage usually should be the
first consideration in connection with the location and
design of any road. In ahumid climate the water causes

all kinds of soils, except sand, to give way when a load

is applied. To safeguard against the accumulation of water
(1) the road surface should be crowned so as to shed water
off to the side ditches as rapidly as it falls on the road,
(2) whenever the road is in excavation, sutiable side ditches
or gutters should be provided along the sides so that the
water may be conducted to some points where it may be
turned off from the road; (3) whenever it is impracticable
to construct side ditches that will carry the required
amount of water without washing, paved gutters should be
employed; (4) if the material composing the road bed con-
sists of springy earth, some form of under drainage is es-
sential. A line of farm tile laid to proper grade under
each side ditch is, in general, the most satisfactory way
of securing adequate under drainage. (5) Culverts or bridges
should be constructed wherever it is necessary to carry
water across the roadl (6) Avoid turning water from one
intersecting road down the side ditch of another. Also

avoid drainage adjacent fields into the side ditches.

CROWN

 

132

The preper crown to give cross-section of a road
surface depends on two Opposed factors: (a) It is desir-
able to get water away from the surface as quickly as prac-
ticable, so as to prevent the surface material from being
softened by saturation or washed away by water collecting
in, and following along, ruts. (b) It is desirable to
keep the cross-section of a road as flat as is consistent
with good drainage, because traffic distributors itself
over a flat road surface mulch better than over one that
is heavily crowned, and an even distribution of traffic
makes towards uniform wear and comparatively light main-
tenance. There is also less danger of skidding on a road

of flat cross-section than where the surface is crowned.

In general, the amount of crown should be greater
on grades than on level stretches of road, because the
tendency of the water to wash away the surface by collect-
ing in and flowing along ruts depends largley upon the,’
steepness of the grade. An exception for crowning a road
surface apply to cases where the road bed and surface are
of sand. In such case it is preferable that the cross-
section be flat so as to retain as much moisture as prac-

ticableo
WIDTH

The minimum width to accomodate safely two lines

of average horse drawn traffic is 15 ft., and for auto-

A00

mobile traffic the width preferably should not be less than
18 feet. In order to maintsin the travelled way to the
required width and to afford prOper safeguard against ac—
cidents, it is necessary to provide a shoulder not less
than 6 feet along each side of the road way prOper. The
shoulder may have a somewhat steeper crown than the rest

of the road surface, but they should be sufficiently flat
not to endanger traffic using them. Where sharp curves
occur in the alignment it is desirable to increase the

width of the travelled way.

‘GRades: --- In designing a road the most important problem
is the question of maximum allowable grades. In deciding
this question, the advantages to be gained.by reducing all
of the steeper grades on a particular road should be weigh-
ed against the additional lost which the reduction involves.
Whenever changes in grade occur the change should be made

by means of a vertical curve, and not by an abrupt angle.
MATERIALS

Materials for untreated roads include soil, clay,

sand, loam and gravel.

SOils: -—- Soils are classified from the standpoint of
road construction, on the basis of material predominating
in their compasition, texture and structure, permeability,

and capillary power, into clay, sand, loam or gravel. Soils

composed of two different materials mixed in such propor-
tions that the character of the mixture is decidedly inter-
mediate may be deSigned conveniently by naming both compon-

ents, as sand-clay or gravel—clay soils.

CLay: --- Clay is a soil of very fine texture which results
from the complete decomposition of rocks or minerals. Pure
clay is very retentive of moisture and usually becomes
plastic and unstable when wet, but mixed with other materials
such as sand or gravel, its stability may be increased greatly.
No matter how well a clay road is graded and crowned the
surface absorbs water in wet season and subsequent traffic
will produce mud. But when the road is shaped and drained
prOperly it will dry out quickly when the weather becomes
favourable and may soon be restored to its original shape.

On the other hand, clay roads, when dry, usually produce

considerable dust under traffic.

SAnd: --- Sand is composed of granular particles of mineral
or stone which occur in nature and which will pass a i inch
mesh screen. The & inch mesh screen is an arbitrary divid-
ing line between sand and gravel and is generally acdepted.
Nearly all sand ccnsists essentially of quartz grains that
are very hard and durable. But there is no cohesion be-
tween the different grains and, therefore, soils composed
principally of sand are unstable, except when confined

in some way. Dry sand offers almost as great resistance

to traffic as mud, and except in very wet seasons sandy roads

155

are likely to dry out to a considerable depth. Sand roads
are at their best when they are kept moist, and for this
reason they should be designed with a view to retaining
moisture in the sand rather than to effective drainage,

as in the ass with clay roads. Such road are improved

by mixing with clay.

LOam: --- Loam is a soil composed of clay and sand, mixed
with a considerable percentage of finely divided vegetable
matter or humus. The quality of load from the standpoint
of road building depends very largely upon the prOportions
in which sand and clay are present. Loam is drained easily
and is fairly stable even.when wet. Another advantage is
that it will not become very dusty under traffic in dry
weather and frequently will cement fogether into a very
hard, compact surface. Roads surfaced with such materials

are generally called "top soil" roads.

”GRAvel:“—-- Gravel is made up of small rounded particles
of stone which occur in nature and are sufficiently large
to be retained on a & inch mesh screen. In general, when
a soil contains as much as 40 to 50 per cent of gravel and
sufficiently clay or other cementing material to bind the
gravel particles together, it proves a very satisfactory
material for construction of roads, because it is drained

easily and is very stable when compacted.

CONSTRUCTION METHODS

The work of construction after the general location
and design have been decided upon, may be separated into
six more or less distinct operations, viz., (l) The work
is staked out in accordance with reviously prepared plans
(2) the right of way is cleared of all trees, brush etc.,
which would interfere with work; (3) all necessary bridges,
culverts, drains, and other structures which extend under
the road surface are constructed in accordance with proper
design; (4) the road bed is brought to the required width
and grade by making excavations and constructing embank-
ments; (5) the surface is finished and so maintained un-
til compacted thoroughly; and (6) all necessary outlet
ditches, gutters, guard rails, fences etc., are constructed in

accordance with the plans.

1. Staking out the work. Before any construction work is

 

started on a road the limits of the work should be marked
clearly by setting line and grade stakes at convenient in-
terval. The same stakes generally are made to serve for
both line and grade, and the space between successive stakes
is made 100 feet. Heavy reference stakes are driven on

each side of the center line sufficiently far out not to

be disturbed during the progress of the work. Supplementary
stakes necessary for making the tops and bottoms of slopes
and ditch lines may be set from the reference stakes by
means of a string level and a metallic tape.

2. Clearance. After the work has be staked out the right

 

 

137

of way should cleared of all trees, stumps, brush, fences,
etc., which occur within the line of work. Trees that do
not interfere with the work should be trimmed to a neat
contour and left to afford shade.

3. Constructing Culverts, Drains, Etc. All drainage struc-

 

tures extending under the surface of the road should be
completed, and the necessary back fills made over them,

before the work of grading is begun.
EARTH ROADS

Roads constructed by grading the natural soil to
the required shape, grade and alignment, without special
surfacing of any kind are designated as earth roads. The
efficiency of such roads depends on (1) the quality of the
soil composing the road bed, (2) proper construction, and
(Z) adequate maintenance. The grading of an earth road
includes all excavating, hauling and fitting necessary in
constructing the road bed, slopes and side ditches. In
grading the surplus earth in those places above grade is
cut away and filled into those places below grade. Frequently
the grade is established upon an embankment for the pur-
pose of drainage; the earth for the embankment may be brought
in from the sides of the road, that is borrowed; the places
from which it is taken are borrow pits. Mbst of this workv
will be done by manual labour due to lack of mechanical

equipment. There ale however considerable equipment re-

138

leased from the army. This can be used with great advant-
age whereever available. The equipment commonly employed
includes the elevating grader and the wheel scraper. The
elevating grader is employed in grade reduction to load

the earth into dump wagons in which it is hauled to the
fill or waste bank. The elevating grader consists essenti-
ally of a heavy shear plow or disc plow which loosens the
earth and deposits it on a moving canvas apron. When the
wagon is loaded the grader is stopped while the load wagon
is hauled out and an empty ane drawn into position. The
motive power for the elevating grader is either a\tractor
or five or six teams of mules. For many kinds of work,
particularly where frequent turning is necessary or where
the gradient is yielding, mules are preferable to a tractor.
The apron is operated from the rear wheels of the grader.
Generally four mules are hitched to a pusher in the rear

of the grader and sin or eight in the lead. This method
of grade reduction is particularly advantageous when the
material must be hauled a distance of 500 yards or more,
because wagon hauling in such cases is the most economical
method to employ. A tractor mya be used to draw the eleva-
ting grader and one having a commercial rating of 30 to 45
horsepower is required. If the haul is long and the nature
of the end will not permit the use of elevating grader
because of excessive grades or lack of room for turning,
another type which consists of a scoop of about one cubic

yard capacity suspended from a four wheel wagon gear is

139

used. When loading, the scoop is let down and filled.

The pull required to fill this is so great that a tractor

is ordinarily employed. The tractor is hitched at the

end of the tongue, without interfering with the team drawing
the grader. One team readily handles the grader after it

is loaded.

The wheel scraper (capacity of about 1% yards) is
employed. For moving earth for distances between 150 and
500 yards. The soil must be loosened with a plow before
it can conveniently be loaded into the wheeler and a heavy
plow is ordinarily employed for this purpose. Two furrows
with the plow will loosen a strip of earth about as wide
as the scoop of the scraper and if more is loosened it
will be packed down by the scraper wheeling in place to
load. A helper or snap team is employed to assist in
loading, after which the wheel scraper is handled by one
team. If a road has been graded so that the profile is
satisfactory, and the surface is to be shaped to a pre-
scribed cross-section, either the elevating grader or the

wheel scraper may be used.

MAINTENANCE

Regardless of the care with which an earth road has
been graded, it will be yielding for a long time after the
completion of the work. It will also readily absorb water.

The condition of the surface will naturally deteriorate

 

140

rapidly during the first season unless the road receives
the constant maintenance that is prerequisite to satisfac-
tory serviceability. The road drag is generally recommend-
ed for this purpose, and if the drag is properly used it
will serve to restore the shape of the surface as fast as
it is destroyed by the traffic. The best time to drag

is as soon after a rain as the road has dried out enough

to pack under traffic. If the work is done while the road
is too wet, the first vehicles travelling the road after

it has been dragged will make ruts and to a considerable
extent offset the good done by the drag. If the road is
too dry, the drag will not smooth the irregularities. A
little observation will be required to determine the preper
time for dragging on any particular soil, but usually after
a rain or thaw there is a period lasting a day or two when
conditions are about right. The drag is used merely to
restore the shape of the surface and to do so a small amount
of material is drawn towards the middle of the road. But
there must be a ridge of loose material left in the middle
when the work is completed. By shifting his weight on

the drag the Operator can adjust the cutting edge so that
very little loose material is moved cross wise of the road
which is the preper method to pursue. In that case no

edge will remain at the middle of the road. If a slight
one is left it should be removed with a final trip with

the drag., In addition to dragging, weeds must be out along

141

the read about twice a year, the ditches must be kept cleaned

out and culverts open.

All of the maintenance for 10 miles of earth road
can be accomplished by one man giving his entire time to

the work.
SAND CLAY ROADS

A road surface constructed of sand and clay, mixed
in proper proportion, possesses the resisting power of
sand in wet season and of clay in dry season, and frequently
is superior to either in all seasons. Ordinarily each
road frequently contains short sections which are constructed
of such soils, and it happens occasionally that for a con-
siderable distance along a road the soil contains just the‘
prOper prOportion of sand and clay to produce an excellent
road surface for moderate traffic under all weather condi-
tions to which the road is subjected. But, in general,
such soils occur only for limited distances, and to secure
a continuous surface of this kind, the necessary material
must be hauled to the road, spread and compacted after the
grading is completed other wise. Generally the soil com-
posing the road is deficient in only one of the necessary
constituents sand or clay, and it frequently may be economi-
cal to construct the surface by supplying the necessary
sand or clay and mixing it with the natural soil of the

road—bed, rather than to provide a surface of natural sand-

. 142

clay material.

The construction of sand-clay roads is essentially
a matter of employing locally available materials to the
best practical advantage in producing an improved earth
road surface. To do this involves an intelligent selec-
tion from the local materials and an adoption of the con-

struction methods em loyed to the material selected.
SELECTION OF KATERIALS

The questions that ordinarily must be given princi-
pal consideration in the selection of materials for a
sandy-clay road surface are: Is the soil such that, if
local sand or clay were mixed with it in preper prOportion,
a durable road surface can be produced? (2) Is top soil
of a suitable character available for use as a surface
material? (3) Can a sufficient quantity of natural sand-
clay subsoil for surfacing the road be obtained conveniently?
(4) Can the two constituent materials be obtained separately
and mixed in place on the road?
(5) If a variety of material are available, what selection
or combination would give the best results and prove most

economical in the long run?

In deciding these questions, there are three ways
in which the judgement may be materially assisted. These
are by means of (l) surface comparison, (2) field examina-

tions, and (3) laboratory tests. These are dealt with in

.L‘i‘U

detail in Chapter III.
TOP SOIL

The best top soil for road surfacing is usually found
in fields which have been under cultivation for a number
of years. The probable reason for this is not only that
cultivation produces a more intimate mixture of the soil
constituents, but th t the repeated aeration tends to im-
prove the stability of the soil by causing the oxidation.
If certain component minerals. Also, where the original
soil contains too high a percentage of clay, cultivation
may have improved its quality by increasing the rate at
which clay is leached out. Since cultivation ordinarily
extends to a depth of only a few inches below the ground
surface, the layer of soil suited for use in road surfac-

ing is, in most cases, very thin.

The safest guide in identifying top soil that will
make a satisfactory mend already constructed of soil in ques-
tion. The following list of characteristics which distin-
quish top soil of a satisfactory quality may prove help-

ful in selecting the soil.

1. Top Soils of granite origin are usually good.
2. Good top soil usually has a very 'gritty' texture, and
when rubbed between the fingers the characteristic should

seem more pronounced than any other.

 

144

5. Samples of soils taken from a number of first class

tap soils have shown an average sand contents of 50 to 75
percent and an average clay contents of_from 25 to 50
percent. But satisfactory results have been obtained most
frequently where the sand contents ranged between 65 and 70
percent.

4‘ The colour of good top soil is usually gray, but colour
is by no means an indix to quality.

5. Soils which are rated as good quality for agriculture by

farmers possess the proper characteristic for a good quality

of tOp-soil for roads.
CONSTRUCTION METHODS'

The choice of methods to employ in constructing a
sand-clay road surface depends on the local condition. In
general, there are four distinct sets of condition, all of
which may occur in the dams locality, or even on different
sections of the same road. .

1. When the original road bed is sandy and it is desired

to construct the surface by admixing clay.

2. Where the original road bed is composed of clay and it

is desired to construct the surface by admixing sand.

3. Where it is desired to construct the surface of top

soil or other natural sand-clay mixture without admixing

any of the road bed material.

4. Where it is desired to supply the sand and clay separately

and mix the two materials together in place to form the

.L'IU

surface.

The general ends which all of the construction
methods should aim to attain are as follows: --- (l) The
question of location, design, drainage, grading, etc., are
more important in the case of sand-clay roads. (2) The
amount of clay contained in a finished sand-clay surface
should be only slightly more than sufficient to fill all
the voids in the sand and would normally be 50 to 55 p.

(5) For average country road traffic and a stable road-
bed, the depth of sand-clay surface should be about 8 inches
after it is compacted. (4) In constructing a sand-clay
surface, the two constituents materials should be thorough-
ly and intimately mixed together in all cases. (5) No
matter what method is followed in constructing a sand-clay
surface, traffic usually must be depended upon to puddle

and compact the surfacing materials and the road should
never be considered complete until it has been subjected

to traffic for a considerable period.

The most widely used method is to mix clay or other
binder with the sand. The clay is dumped on the road in
a layer about 8 inches thick and in then mixed into the
sand. It is desired to mix enough sand with the clay to
produce a mixture composed of approximately 1/3 clay and
2/3 sand. The mixing is accomplished in various ways, the

most common being at heavy plow at first and to follow this

146

with a heavy disc narrow. The mixing is a tedious and dis-
agreeable process, but its thorough accomplishment is
indispensible. The mixing is most readily done when the
materials are saturated with water and in practice it is
customary to depend upon rain for water, although in the
final stage water may be hauled and sprinkled on the road
to facilitate final completion of the mixing. After the
mixing has been completed, the surface is smoothed with
blade grader and is kept smooth until it dries out. Re-
peated dragging would be required, during the first year
especially, and to some extent each year in order to keep
the surface smooth, but the dragging can be successfully
accomplished only when the road is wet. In regions where
several months of continued hot, dry weather is to be ex-
pected each year, the sand-clay mixture is likely to break
down unless it is of considerable thickness and generally
the surface layer is made much thicker than for regions
where the annual rainfall is fairly well distributed. This
is especially necessary when the binder is of inferior
quality. It is not uncommon in such cases to make sand-

clay surface as much as two feet thick.

As the mixing progresses it may appear that patches
here and there daficient either in clay or sand and the
mixture in these places is corrected by the addition of a
little sand, clay as may be required. If the tap soil is

used it is deposited on the sand in the required quantity

147

and is remixed in place to insure uniformity. If either
sand or clay is needed to give a satisfactory mixture,

the preper material is added and mixed in as the work pro-
gresses. The surface is finally smoothed by means of the

grader and drag.

CHARacteristics: ——- Sand-clay roads do not have sufficient
durability but will be satisfactory for moderate amount

of traffic. These surfaces have maximum serviceability
when moist, not wet, and consequently are not as durable
in dry climates as in humid areas. They are likely to be-
come sticky and unstable in continued wet weather. At
their best, they are dustless, somewhat resilient and of

low tractive resistance.
GRAVEL ROAD SURFACING

Roads that are artificially surfaced with gravel
or within the composition of which gravel predominates, are

called gravel roads.

The ideal gravel road is a mixture of pebbles, sand
and the pieces varying from coarse to fine in such a manner
that when the gravel is compacted into a road surface the
spaces between the large pebbles are filled with the finer
material. The pebbles are of a variety of rock that is
highly resistant to wear so that the road surface made

from the gravel will have the quality of durability. The

148

gravel possesses good cementing properties, insuring that
the pieces will hold together in the road surface. The
cementing property may be due to the rock powder in the

deposit or to mixed with the rock particles, or to both.

The subject can conveniently be dealt with under

two headings:

SELECTION of Gravel: --- Ordinarily the selection of gravel
for use in road surfacing must be confined to local materials
which are or can be made suitable for that purpose. Be-
cause of the high freight the road gravel should not be
transported to a distance more than 100 miles from the

source of supply. The characteristics which the gravel

for road surfacing should possess are as follows: ---

The principal qualities which determine the durability
of pebbles or stone of any kind when placed in a road sur-
face are hardness, toughness, and resistance to wear. The
extent to which pebbles possess these qualities depend
upon largely on the character of the parent stone from
which they were originally produced and accordingly varies
over a wide range. Not infrequently a very casual inspec-
tion will reveal which deposit from a much greater number,
contains the largest percentage of hard durable pebbles.
The most durable pebbles which occur in gravel deposits
are those composed of quartzite. The pebbles which are

least durable are composed of sand stone. Such pebbles

149

are lacking greatly in toughness and will shatter under
traffic. Gravel deposits also may contain a high percent-
age of partially disintegrated pebbles which are even less

durable than sand stone.

THEBBinder: --- No matter how durable may be the pebbles
contained in a given gravel deposit, they cannot be used
successfully in a road surface unless they can be well
bonded together so as to present a combined resistance

to the disturbing action of traffic. To accomplish this
loas requires that the gravel contain some cementing or
binding agent such as iron oxide, carbonate of lime, or
clay. _The principal cementing agent or binder, present
in most gravel deposits is clay, and in case of deposits
which do not carry sufficient binder, clay usually is the

material added to correct the deficiency.
GRADING AND PROPORTIONING

For gravel to make a satisfactory road surface, the
stone particles should be graded in size so that the amount
of binder required will be reduced to a minimum. MOst
gravels deposits as they occur in nature satisfy this re-
quirement in so far as the grading of the pebbles is con-
cerned, but they nearly always contain pebbles of a size
larger that it is desirable to incorporate in a road sur-
face. Natural deposits also not infrequently contain too

large a proportion of sand or clay to produce satisfactory

150

results. The Wisconsin Highway Commission recommends the
following sizes: ---
Bottom Course Gravel --- Bottom course gravel shall consist
of a mixture of gravel, sand and clay with the proportions
and various sizes as follows: --—

I'All to pass a two inch screen and to have at least
60 and not more than 75 per cent retained on a } inch screen;
at least 25 and not more than 75 per cent of the total coarse
aggregate to be retained on a 1 inch screen; at least 65
and not more than 85 per cant of the total aggregate to be

retained on a ZOO-mesh sieve."

Top Course Gravel --- Top course shall consist of a mixture
of gravel, sand and clay with the prOportions of the various
sizes as follows: -—-

"All to pass a 1 inch screen and to have at least
50 and not more than 75 per cent retained on a & inch
screen; at least 25 and not more than 75 per cent of the
total course aggregate to be retained on a one-half inch
screen; at least 65 and not more than 85 per cent of the
total fine aggregate (material under 4 inch in size) to

be retained on a 200-mesh sieve.

The thickness of the layer of gravel required de-

pends both upon the type of soil upon which it is placed

 

151

and the nature of the traffic to which the road would be
subjected. For secondary highways a layer 8 inch thick
will be sufficient. In dry climates, a layer six inches
thick will be adequate if it can be kept from ravelling.
On secondary roads, carrying principally farm to market
traffic, and not a great volume of that, the above thick—

ness may be reduced to 4 inches.

CONSTRUCTION Methods: --- Thdee methods generally used are
as follows: —-- (l) Trench method; in which a trench nar-
rower than the graded width is filled with gravel; (2) The
trench and feather edge; in which a trench about 16 or 18
feet wide is filled with gravel. This is covered with a
top course of gravel which extends to the full width of

the shoulders, and (5) The feather edge method; which con-
sists of a surface for the full width of roadway, that is,
out to out of shoulders. It varies in depth from a maximum
at the centre of the road to one or two inches at the edges.
A uniform depth of material for the full shoulder width is

also used.

TRENCH Method: --- A trench of a prOper width and depth

for receiving the gravel is excavated in the earht road
surface and the gravel is placed there in. The trench is
foamed by plowing a few furrows and scrpaing out the loosened
earth with a blade grader. The loose material is generally

moved out laterally to build up earth berms or 'shoulders'

152

alongside the gravel. In to this trench the gravel is
dumped in the proper quantity to give the required thick-
ness after being compacted. The greatest care must be
exercised in spreading the gravel to eliminate uneveness
where the loads were deposited. An ordinary blade grader

is one of the best and most economical implements to use

for spreading the gravel. Shen the gravel has been deposit-
ed in the trench for a distance of a thousand feet or more,
the spreading is accomplished by dragging the surface re-
peatedly with the blade grader, the work being continued
until all waviness disappears. The gravel is then thorough-'
ly and repeatedly harrowed with a heavy stiff tooth harrow
to mix thoroughly the fine and coarse gravel so as to pro-
duce as nearly a uniform mixture as possible. The gravel
may be compacted by rolling or allowed to pack from the
action of traffic. The rolling is performed with a three-
wheeled seff prepelled roller weighing about 8 tons and
must be done when gravel is wet. In the absence of rain-
fall a sprinkling wagon is used to wet down the gravel.
The gravel must be spread in layers not over 5 or 6 inches
thick to get the desired result, which means that for an
ordinary gravel road about 10 inch thick, the gravel will

be placed in two layers of about equal thickness, each of

which will be rolled.

If a gravel is placed in a trench in dense soil and

rainy weather ensues sufficient water will be held in the

153

trench to cause unevenness from foundation settlement and
the gravel will become mixed with the soil to some extent
and be thereby wasted. Trenches cut from the road bed
upon which the gravel is placed, to the side ditches, will
relieve this condition by affording an outlet for the sur—
plus water. Nevertheless some difficulty may be expected
if the trench method is used and wet weather prevails.
Moreover, in long continued dry weather, the dispersion
'and loss of considerable gravel from the action of auto-
mobile traffic is avoided because the gravel is held be-
tween substantial earhh-berms and the gravel will peak
better and hold its shape longer by the trench method than

otherwise.

THE Feather Edge Method: --- The gravel is dumped upon a
prOperly shaped sub-grade and spread with shovels and rakes.
A heavy tooth-harrow will aid in distributing and mixing
the gravel, also, a scraping grader will be found advantage-
ous for spreading it. This gravel by the loose method,
which is not recommended, is spread only 5 or 4 inches

deep and allowed to be consolidated by the traffic. Then
another layer placed upon it and packed in the same manner
and this process continued until the required thickness

is obtained. From time to time after rains while this is
going on the road should be smoothed and shpaed by road
drag. With the compressed method after harrowing and

shaping a roller is placed upon the road and the rolling

154

continued until a firm surface is produced. During the
last of the rolling the surface should be sprinkled with
water to assist with the compacting. Most road men prefer
to have the gravel deposited in comparatibely thin layers
so that it is compacted from the bottom up and is equally

dense throughout.
MAINTENANCE

Gravel surfaces require careful maintenance, cepeci-
ally during the first season the road is used. The gravel
will compact slowly and during the process will be rutted
and otherwise disturbed by traffic. It is important dur-
ing this peridd to restore the shape once a week or at
least twice a month. The light blade grader is usually

employed for the purpose.
BROKEN-STONE ROAD SURFACES

The broken stone road surface or macadam road, con-

sists of a layer of broken stone, bonded and cemented to-

gether by means of stone dust and water. The surface may

or may not be coated with some bituminous material.

MATERIALS

Crushed lime stone and dolomite are used most ex—
tensively for building water bound macadam surfaces and

foundations because they possess the essential properties

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of hardness and toughness andbecause the fine particles
obtained in crushing, when mixed with water, form a na—
tural cement. Crushed blast-furnace slag, crushed trap

rock, crushed granite, and crushed boulders are also used.

TYPICAL CROSS—SECTIONS

Water bound-macadam roads usually have a trench
section, typical dimensions and detsils of which are illus-
trated in Fig. l and 2. In the construction shown in Fig. l,
the macadam surface consists of a base course (a) and a
top course (b) Where the subgrade is poor, it is necessary
to provide a sub—base. This may be 8 inches telford founda-
tion which consist of a layer of hand-laid stone blocks,
as shown at (c) a course of gravel 6.to 8 inches thick,
as at (d) or a course of field stone 6 to 10 inch thick,
as at (c). In the construction illustrated in Fig. 2,
the tOp course (a) of waterébound macadam is supported on
an 8 inch telford base course (f) and a 2 inch to 5 inch
leveling course (g) of crushed stones, containing enough
spalls to make a dense mass. The léveling course is rolled
do as to fill the irregularities intthe surface of the base
course and to provide firm and even support for the surface

course.
PROPERTIES OF THE STONE

The stone should be structurally sound, reasonably

156

hard and tough, and the dust resulting from crushing

when mixed with water should have cementing properties.
Since the traffic may vary from very light on some roads,
to far beyond the limit of the economical capacity of this
type of pavement on others, it follows that any particular
deposit of stone might be entirely inadequate. A maximum
wear of 6 to 8% in the Deval abrasion test is generally
recommended for crushed stone. A unit of weight of 60 to
65 pounds per cubic feet is widely used to control the
quality of blast—furnace slag. A percentage of wear of

57 to 40 after 500 revolutionsin the Los Angeles abrasion
machine“; bettenjtest of quality for broken stone for water-

bound macadam.
SIZE AND GRADING

The same size of crushed stone or crushed slag is
generally used in all courses or layers of water bound
macadam surfaces because of the convenience of storing and
handling. Soft stone should be larger than hard stone be-
cause it fractures to a great extent when rolled. The
A.A.S.H.D. (American Association of State Highway Officials)

recommends two sizes of crushed stones as follows:

 

9 American Association of State Highway Officials.

(1947)
Standard Specifications for Highway Materials

5 Method of Samplingld Testing. Washington D.C.

157

1 to 2 inches
Passing sieves 2%" 2" 1%" 1"

Percnntage 100 90-100 35-70 0-15

2 to 5 inches
Passing sieves 5%" 5" 2"

Percentage 100 90-100 O—15

A combination of foregoing two sizes also is used. Larger
size stones are sometimes specified, but they are extreme—

ly difficult to spread and obtain a true surface.

The specifications of the A.A.S.H.D. provide two
sizes of screenings for filling the voids in water-bound

macadam, as follows: ---

O to No. 4 Sieve

Sieve No. 5/8" No. 4 No. 100
Percentage passing lOO 85-100 10-50

0 to % inch Sieve
Sieve No. %" 4“ No. 100
Percentage passigg 100 90—100 lO-ZO

CRown: --- The crown of a macadam surface may be made some-
what flatter than gravel but slightly greater than paved

surfaces. The normal crown may be from 4" to 5/8" per foot.

WIdth: --- Macadam may be made single track of 8 to 10

ft. or double track of 16 to 20 ft. or wider, as conditions

158

demand. Wider widths tend to spread traffic and prevent

it from running in lanes, thus tending to reduce cutting.

THICKness: --- The thickness of macadam is usually simply
chosen and by experience is found to range from 6 to 9
inches with 8 inches being perhaps the most common. The
Massachusetts Highway Department has developed the follow-

ing formula:

t = w
41)

Where t is the thick ess in inches, W is the wheel load
in pounds, and p is the supporting power of the soil in

pounds per sq. inch.

Harger and Bomey (————) presented a somewhat more
rational formula by including a term T, the width of the

tyre in inches. The formula is:

t . w - T2. - T/S
135—9"

In using these formulas an allowance for impact of 50 per-
cent should be added to the static wheel load and the tyre

width should conform to legal requirements.
CONSTRUCTION
SUB-GRADE

The sub-grade should be compacted as uniformly as
possible. The preparation of the subgrade is especially

important because a water bound macadam layer not only is

159

flexible but it cannot be reshaped, as can a gravel layer,
by means of a blade grader or similar machine. Some method
of stabilization may be necessary on some soils, particular-
ly sand and silt. High capillary and elastic clay subgrades
are very unsatisfactory and should be stabilized. Water
bound macadam layers are almost always constructed by
trenching the subgrade to obtain the necessary quality

of earth for shoulders. The earth shoulders are often

used to confine the edges of the broken-stone layers, but
much more satisfactory results will be secured by having
side forms for each layer, which are kept in place until

the layer has been rolled and bound. The shoulders should
be shaped and compacted adjacent to the edges of the lower
course of broken stone before the stone for the upper course

is spread in order to give side support.
PLACING THE STONE

The placing of the broken stone is an exceedingly
important part of the construction of a water bound macadam
layer. It is essential that the stone be spread uniformly
in order to obtain a surface which will have smooth riding
qualities. Dumping the stone in large piles on the sub—
grade and spreading it out from,these piles usually results
in the segregation of sizes, the stone which is left in
the original pile is more compact than that in surrounding

areas, and uniform compression by means of rolling is prac—

160

tically impossible. Dumping the stones on platforms along
the sides of the roadway and to place the stones by means
of hand shovels is the method generally adepted. This

has been supplanted very largely by the use of the mechanic-

alespreader in mechanized countries.

It has been formed impracticable prOperly to roll
a greater thickness than about 5 or 6 inches of loose stone,
therefore, the stone for the macadam surface is usually
placed in two layers, the first or lower being rolled be-
forethe next layer is placed. In order to secure the pro-
per or uniform thickness of a course of broken stone, side
boards, or forms, of correct height are necessary. Centre
boards sometimes are used.but row of stakes set at proper
elevations or of blocks equal in height to the correct
depth of the loose layer are most satisfactory. String
grades are also used for this purpose. The necessity of
prOperly preparing the subgrade and of having its sur-
face parallel to the finished surface is apparent. A check
of the placing of the stone may be secured by calculating
the longitudinal distance which each load of stone should

9

cover.

ROLLING

After the stone has been placed, it is rolled with
a heavy roller which is of the three-wheel, or macadam,

type and weighs not less than 10 tons. Rolling should be-

161

gin at the sides of the broken-stone layer and should
overlap the shoulders for a distance of 12 to 18 inches.
It should progress gradually towards the centre, parallel
to the longitudinal axis of the road, with a uniform over-
lap on each succeeding trip of the roller. Rolling is
continued until the stone has become thoroughly keyed;
this condition is reached when the stone no longer creeps
or waves ahead of the roller. During the first trip of
the roller, low places may develOp in the stone layers
they should be corrected by slightly roughening the sur-

face and adding more stone.
APPLICATION OF SCREENINGS

The screenings may be spread by means of mechanical
spreader or by hand. When hand methods are used, the screen-
ings should be deposited in piles along the roadway on a
dumping board and broadcast over the surface with shovels
with a circular sweeping motion to a depth just sufficient
to cover the stone. The surface is now broomed with fibre
brooms which push the screening into the void spaces in
the stone. The broken stone layer then is sprinkled with
water and more screenings added when necessary. The sprinkl-
ing, adding screenings, sweeping, and rolling is known .
as 'puddling' and is a very important part of the construc-
tion of a macadam layer. The puddling operation is continued

until a wave of grout flushes ahead of the roller. The

162

quantity of screenings required to fill a water-bound
macadam layer will vary according to the size and quality
of the coarse stone, the size of the screenings, and the
amount of puddling, and generally will be equal to about
20 per'cent of the volume of the compacted layer for the
base and intermediate courses, and about 25 per cent for
the top course. A water bound macadam layer must be al-
lowed to dry out before placing a bituminous treatment or

wearing course.
MAINTENANCE

The first effect of traffic would be to brush tray
the fine materials used for bonding the surface, thus ex-
posing the large stones in such a way that they are rather
easily loosened and removed from the surface by wheels and
the hoofs of animals. This finer material must be replaced
as fast as it is removed so as to protect the surface.
Either stone dust or clayey sand may be used, but clay if
used alone is likely to be sticky when wet and prove to
be worse than the condition it was expected to correct.

In time, ruts and depressions will appear, either as the
gradual effect of wear, which will inevitably affect some
portions of the surface more than others, or on account
of subsidence of the foundation. Uneven places are re-
paired by first loosening the stone, then restoring the

cross section by adding new materials and tamping or rolling

it in place.

163

CHAPTERJVII
LOCATION AND DESIGN
LOCATION

Location is the first important consideration in
planning the construction Of a road. Low cost roads are
no exception to this rule and should be so planned as to
make it possible to convert them into higher type roads
as traffic and availability of funds warrant or permit.
It is not possible to lay down a universal rule regarding
location of a road. The major considerations are: ---
1. Relative cost Of construction
2. Convenience Of Public
5. The safety and comfort Of travellers
4. Character of traffic in the area
5. Destination of traffic
6. Saving of distance
7. Cost of maintenance
8. Topography

9. Reasonable consideration to the pleasing features.

ROAD DESIGN

The volume Of traffic is the primary factor in de-
ciding the design Of the road to be built. Volume is de-
termined on the basis of traffic in a 24 hours period at

the peak of traffic. TOpography is the second important

164

consideration, e. g. the same standards as to alignment,
grade and cross-section cannot be maintained in mountainous
location as in level country. In considering the design
of low cost roads it is well to separate them into two
groups. (1) Those roads which, at present and for many
years to come, will carry only a very limited volume and
weight of traffic. (2) Those roads which must have a
low cost surfacing at the present, but which will eventu—
ally have sufficient traffic to require a more expensive
paving. 0n the roads of the first group the standard for
design may be inferior. The location grade and alignment
of the second group should be very carefully considered
because the prnsent construction is only the first stage
of develOpment, and unless this first stage is designed
with future requirements in view the initial investment
will be mostly wasted and can not be utilized as a proper

foundation for the successive stages of improvement.

DESIGN OF GROUP I

On roads in this group, grades as steep as 10 per
cent and curves as sharp as 100 feet radius may be used,
with very little cutting off of knolls or filling up of
long hollows. Low cost untreated surfaces will not shed
water like hard pavements, and therefore absolutely level
grades should be avoided whenever possible. In hillside

locations contours in general should be followed, cutting

165

through the lepes is more economical. Changes in grades
should not be too abrupt and should always be rounded off
with a vertical curve of sufficient length to give a sight
distance of at least 200 feet. Grades of over 5 per cent
on sharp curves may be compensated a little to facilitate
upward-bound traffic. A reduction in grade of l per cent
rcr each 50 feet in radius shorter than 200 feet will usual-
ly be sufficient compensation. Whenever possible the road
should be kept off boggy soil, but location involving ex-
cessive hard rock excavation should be avoided. The width
of road will depend on the nature of the topography, but
in general the travel way need not be more than 18 feet,
with 4-foot. shoulders, making 26 feet from ditch to ditch.
The width of roadway should be increased from 2-6 feet

on curves, and super-elevation should be provided even

where no surfacing is to be placed.

DESIGN of Group 2:.--- Roads which will later carry consider-
able traffic should be laid out and graded with consider-
able care. The road should be reasonably straight, but

long straight grades and tangents are not necessary or
desirable except in level country. Gently rolling grades
should be used, and in general the maximum should not ex-
ceed 7 percent, but to avoid sharp curvature grades as

steep as 9 per cent may properly be used. The minimum
radius of curve should be 500 ft. except in mountainous

location, where 100 feet radius may be used for inside

curves, and 200 feet for outside or blend curves. The
sight distance at horizontal curves should not be less

than 300 feet. Vertical curves are used at all breaks

in grades over 1 per cent. Sufficient length of vertical
curves is used to insure a clear sight distance over the
hill of at least 250 feet. Grades over 5 percent or curves
of less than SOC-feet radius should be compensated. All
curves of less than 1000-foot radius should be widened, and
all curves of less than 2000-foot radius have to be super-
elevated. It is customary to use a maximum superelevation
of 1 inch per foot width of road-way for curves up to 1000
foot radius and about one-half inch per foot for those

of 2000 feet. A width of roadway of 28 feet, ditch to
ditch, will ordinarily be sufficient for many years to come,
but in flat country wider sections are low in cost. The

35 feet width will permit ZO-foot surfacing with 4 foot
shoulders. The embankment slope should preferably be as
flat as 3 to l, in order to encourage the growth of grass
which will protect the shape from erosion. Ditch bottom
and shoulder lines should be rounded to facilitate mowing
weeds. The shoulders should be mowed and seeded to protect

them from erosion due to rain and flood.

Excessive reduction of intermediate grade, extra
expense to get long straight grades, and too few relocations

to secure maximum grade should be avoided.

167

RIGHT OF WAY

A difficult and annoying problem with which all
highway engineers have to deal with is the right-of-way.
Estimates for the right-of-way should, therefore, be made
with future.requirements in view. It is difficult and ex-
pensive to secure additional right-of-way at any time after
the initial construction has been started because the cost
mounts as the years roll by. The minimum standard widths
vary from 80 to 100 feet for main roads and from 60 to 80
feet for secondary roads. These adopted minimum standard
widths appear reasonable for any width of road that present

or future traffic might require.

VISIBILITY

Conditions for good visibility or safe sight distance
must be provided for preventing accidents to vehicles
moving at a higher speed. Sharp changes from tangents to
short radius curves, or from long radius to short radius
curves, or from long radius to short radius curves should
be avoided. As a general rule long tangents should be
Joined by long radius curves. In level country this can
be done at little extra cost. Slight changes in direction
for the sake of visibility should be made on summits rather
than in valleys. Where this in unavoidable on summits,
the horizontal curve should extend, if possible, beyond

the ends of the vertical curve.

168

The Pennsylvania Department of Highways determined
the distance required to bring a car to a stop for various
speeds on grades varying from level to 8 percent, on a dry
concrete surface. Their tests indicate that for a speed
of 60 m.p.h. on a level grade, a car equipped with four-
wheel brakes requires at least 216 feet to be brought to
a stop. Assuming that an allowance of one second is made
for each driver, in terms of distance this means 176 ft.,
which added to the actual minimum breaking distance, gives
608 feet. Therefore the minimum clear vision distance that
should be used on all roads should be approximately 600
ft. This should be applied to both horizontal and vertical

curves.

An added reason for the importance of good visibility
on vertical curves is the fact that the driver cannot see
low objects 0n the road, such as children and animals.

When the alignment is generally straight for long distance,
a special effort should be made to provide at least the
minimum clear distance of 600 feet except under special
conditions. 0n long stretches of road which are generally
straight, drivers become accustomed to expecting safe con-

ditions and blind spots are the cause of frequent accidents.

Special attention should be given to the elimination
of blind Spots that occur by a combination of horizontal

and vertical curves. Each of these classes of curves should

169

meet acceptable standards for clear vision distances.

Road intersections present another phase of the sub-
Ject of visibility. The widening of approaches is desir—
able; that is, on intersections where paved surfaces are
20 feet wide, an additional lane should be provided on each
side, making a total width of 40 feet back from the inter-

section for 150 feet to 200 feet.
DANGER SIGNALS, ROADSIDE DESTRUCTIONS

There are many points on roads where the desired
visibility cannot be obtained by relocation without great
wxpense. The points often present danger hazards with
frequent accidents. Such curves must be handled by ample
and unmistakable warning signs. 0n curves, both horizontal,
and vertical, where visibility is restricted, traffic lines
should be painted on the pavement surface. ldvanced warn—
ings, with appropriate wording, placed at conspicuous lo-
cations, should be provided. For night drivers, warning
signs of the reflector type should be placed at sharp
curves, road intersections, and other dangerous points.
Roadside trees and thick undergrowth should be trimmed
out where clear view is obstructed. This feature may be
carried out without destroying the natural beauty of wooded

areas.

170

DRAINAGE FACTOR

Level grades are allowable when drainage can be
carried from the roadway by the transverse slopes when the
roadway is through cuts absence of at least a light gradient
necessitates special design of the roadway ditch to carry
side drainage. In level country special roadway ditches
may be designed on a wide turnpike section. Economy and
consideration of'adjacent prOperty may dictate uniform
depth of side ditches in which ease roadway grade eleva-
tion will be controlled by side drainage. Five-tenths
percent minimum grade for drainage is usually required al-

though one percent is preferable.
MAXIIUM GRADE LIhITS

Under normal conditions high gear will efficiently
carry heavy trucks up maximum sustained grade of about 3
percent. Automobiles with similarly operate up at about
7 percent sustained maximum grade. Grades in excess of
7 percent become disadvantageous to all vehicles. Six
percent is a preferable maximum for general use and for
sustained grades. Maintenance of uniform safe speed is a

convenient measure of the desirable grade.

BRIDGES AND CULVERTS

Locations are often badly made on account of the

desire to utilize an existing old bridge. Avoid putting
angles on curves in new roads to utilize an old bridge.

In all circimstances culvert headwalls should be beyond

the edges of the earth shoulders. For structures on curves
the distance between head-wall shall be not less than 30
feet, or prevailing roadway width. Approaches to bridges
should be on a tangent even though necessary to skew the
bridge to obtain it. Skew should be as small as possible.
An angle over 45 degrees is objectionable, and an angle
over 60 degrees should never be used. Direction of channel
can frequently be changed at small cost. Often embankment
material is needed which will justify an extensive channel

improvement.
PREPARATION 02 ROAD PLANS AND SURVEYS

A good set of plans can be prepared only when the
field survey, designing, estimating, and field inspection
have been carefully executed neglect of any of these pre-
paratory Operations in the name of economy will result in
errors, higher cost, and greater expense on maintenance.
Six steps are necessary in the collection of data and
compilation of plans. (1) Field surveys (2) Mapping
the survey (3) Designing the road (4) Estimating the
quantities (5) Field inspection of the design (6) Final

completion of the plans.

Care and skill is necessary that the centre line

I72

as located will be the best possible within the limits of
justifiable expenditure. The final location field survey
follows in general a route tentatively established. It

may be along an existing road or even an entirely new

route, but the route should have been examined with certain
definite ideas in mind by the locating engineer or the chief

of party acting under instructions.

The mapping of data which have been accumulated by
the field surveys furnishes the base upon which to build
the design. The road design consists of several parts.
(1) Type of surface (2) Width and shape of section
(3) Proper Drainage (4) Correct grade line. (5) Deter-
mination of quantities (6) Culverts and bridges needed

(7) Riscellaneous details.

The type of surface has been discussed. The width
of the surfacing, the shape of section, the width of the
shoulders, the slope, width and depth of ditches are deter-
mined, and this information is furnished to the drafting
office where the design is made in accordance with the
tentative specification and requirement as set up for the
road. Throughout the design the designer must constantly
check for drainage. Special drainage may be required in
some places. The designer should observe that the maxi-
mum gradient having been determined, it is uneconomical

and unwise to make heavy and extensive cuts to secure a

175

lower grade at points on the road where the traffic condi—
tions remain the same. The most economical grade line is
one where the cuts and falls balance with a minimum of
excavation. This is usually never attained, but can be
closely approached. The controlling features of the grade
must be satisfied. The economic design will make use of
rolling grades. It is unwise to cut a 5 per cent grade

to 2.5 per cent of the ruling grade is 5 per cent. Small
minor rises and hummocks, however, should be cut through
to get a pleasing grade line and avoid the unsightly appear-
ance of dips in the road. In computing the yardage, and
balancing the earthwork, shrinkage of the material placed
in embankment must be taken into account. The allowance
for shrinkage will vary from 15 to 35 per cent, depending

on the amount of sod and surface mulch.

To determine an economic grade line a template
cut to the road section is placed over the plotted ground
cross-section and adjusted to make the side out and fill
balance. The elevation of grade as shown by this position
of the template is marked upon the profile at the proper
station. Through these plotted points, a straight line
curve is drawn which will be an economic grade line; that
is, the earthwork quantities will be balanced both for
side casting and for longitudinal movement. The line must
be adjusted to take account of the various vertical control

points along the line, such as rail-roads, bridges, culverts,

and cross roads. The first line drawn is a trial grade.
From this trial a preliminary estimate of the earth quantities
is r n off and the grade line is adjusted to make the cuts

/

and fills balance.
FIELD INSPECTION OF DESIGN

The plan at first prepared may and usually does
contain inconsistencies and omissions which must be correct-
ed. The Engineer walks over the line and carefully checks
the grade and sees that the fills are adequate in swampy I
places, that guard rail is specified at all places where
essential; that the cuts do not unnecessarily interfere
with private property. He should not criticize a grade
because at that particular point it dees not appear to
fit the ground properly. If a desirable grade has been
properly laid, the cuts and fills as shown on the plan are
necessary to produce that grade. He should, however, cri-
ticize the grade with regard to general topography, the
importance of the road and the roads relation to general

topography.

The general drainage conditions should be given
careful consideration; inspection of bridges and culverts
on the same stream should be made to see that proper sizes
are specified. Notations as to private drives, cross road
intersections and railroad crossings, should be made. The

engineer should endeavor to visualize the road as it will

be in the future and in this manner check the work of the

designer at all points.

FINAL PLANS

The field inspected plans are scrutinized by the
designer to see what changes are pointed out by the field
Engineer. These are studied with reference to the general
idea of the grade and line. Recommended changes in grade
must be given consideration. The yardage quantities are
recomputed.. The elevation of all stations all the grade
line are now placed along the bottom of the sheet. Eleva—
tion of other essential points are shown, bench marks are
noted, guard rails computed, length of vertical curves

are shown, and special drainage details described.

New culvert information should be most carefully
studied and the proper kind, size, and shape of culvert
specified. Special details and designs should be worked
out on separate sheets and included in the set of plans.
The set of plans when completed should be collected in
folio form and arranged in order; the cover sheet showing
the general location of the project with respect to ship-
ping points by rail, and the road leading from these ship—
ping points to the job, one or more sheets showing the
standard cross sections for the road construction: the

plan-profile sheet for the entire layout; quantity sheet

consolidating and summarizing all the quantities of work
of every kind upon the project; sheet showing the special

details; cross section sheets, and mass diagram sheet.

177

CHAPTER VII

CONCLUSIONS AND RECOMMENDATIONS

Pakistan's first concern is to effectively utilize all
available resources, in order to build up an economy
worthy of the fifth largest nation in the world. An
efficient road system is a prerequisite for the full
exploitation of the vast potential wealth in the country,
for technological scientific progress, and for raising
the standard of life and living in rural areas.

A commonly accepted American Standard placed the road
requirements of different types of area, according‘to the
stage of their development as follows:-

Type of Country Miles of Road Per
Square Mile of Area

Highly developed industrial area 2.3
Highly developed agricultural area 1.?
Well developed hilly area 1.4
Mountain area ' 0.7
Desert Area 0.3

Pakistan has a road mileage of only 0.22 per square mile
area, and thus by this standard has less road mileage
than even a desert area in the United States of America.
On account of many demands on Pakistan's finances for
various developmental projects, it will not be possible,
to entirely meet the needs for roads in the immediate

future. While a six-fold increase in the existing road

178

mileage is the ideal for rural areas according to the
above standard, a two-fold increase is a practical pos-
sibility for the immediate future, and a 3.5 fold increase
is suggested as a target for the next twenty years.

Low cost roads are considered as the right approach for
spreading the benefits, of the funds made available for
roads, over as large an area as possible. Low cost roads
can be built by (a) using locally available material,
thus cutting down the cost of transportation, and (b)
using costly materials sparingly e.g., instead of making
a cement concrete road, a cement stabilized road can be
built by the addition of only 6 to 8 percent cement to
local soil.

Low cost roads include untreated surfaces such as earth,
sand, clay, gravel and stone roads, and stabilized sur-
faces which include mechanically stabilized, cement
stabilized, bitumen stabilized and chemically stabilized
roads. Stabilized road surfaces are considered as being
the most suitable for immediate requirements as these are
(a) low in initial cost, (b) utilize locally available
material, (c) are inexpensive to maintain as they need
less frequent dragging, blading, and reworking, and

(d) provide greater safety and comfort as loose pebbles
and dust are eliminated.

The factors which determine the selection of a particular
type of road in a given locality are as follows:-

(a) Availability and cost of materials. The cheapest
materials which give efficient service should be utilized.

179

Proximity to the source of a stabilizing material should
usually mean less cost in the use of this material. As-
phalt is cheaper in areas with oil fields, bitumen near
coal fields and cement near cement factories. (b) Climate.
Climatic factors condition the use of various substances
to stabilize road surfaces. The most important factor
under Pakistan conditions is rainfall. Water plays an
important part in stabilization. It is necessary to

make clay cohesive and provide the medium by which density
can be obtained by compaction. Calcium chloride is a
stabilizing material used in road mixes as it maintains
water in soil due to its delinquescent action. It would
serve no useful purpose in areas of high rainfall such as
Eastern Pakistan, where enough of moisture is always pres-
ent or in very dry areas such as Sind and Balanchistan,
where the air has no moisture to yield. In areas such as
Punjab where the rainfall is around 30 inches, it may be
very effective, by maintaining soil moisture and thereby
reducing soil disintegration. In areas of high rainfall
such as Eastern Pakistan it is advisable to use bituminous
stabilization as bitumen coating helps to waterproof the
road surface and keeps it from being washed away during
rain. In dry weather it helps to check evaporation and
maintain soil moisture. In very dry areas, such as
Baluchistan and Sind, cement stabilized roads offer many
advantages. Most of these area are sandy and the quantity
of cement required is minimal, thereby reducing the cost

materially. (c) Physical properties of soil. Physical

180

properties of the soil play a major part in deciding the
type of surface. Soils predominating in sand are very
suitable for cement stabilization. Soil with high capil—
larity should be stabilized with the addition of bituminous
materials which have the property of not allowing the
water to penetrate through them. Soils containing an
appreciable quantity of sand and clay can be stabilized
by mechanical stabilization. Soil containing gravel has
high internal friction but low cohesion; and can be sta-
bilized by the addition of a suitable binder such as
clay. Calcium chloride can also be used with advantage in
.gravely soil. Soils which have low bearing value are
not suitable for stabilized roads. The only alternative
in this case is the construction of water-bound madadam
roads with a thick Telford foundation to make the bed
stable and resistant to lateral flow.

The following table shows the type of low-cost
road recommended for different types of soil. There are,
however, many limitations to a blanket application of
these recommendations and the final decision should rest
upon the results of actual tests performed in the labora-
tory which would indicate the most economical and durable

surface to be constructed.

Soil type as classified by the
U. 3. Bureau of Roads

 

181

 

3611 Recommended
Group Properties Road Type

Al Well graded material, coarse and fine, Mechanically
excellent binder. High internal stabilized and
friction, high cohesion, no detri- Portland cement
mental shrinkage, expansion capil- stabilized.
larity or elasticity.

A2 Coarse and fine materials, improper' Bitumen stabi-
grading or inferior binder. High lized surface
internal friction and high cohesion and chemically
under certain conditions. May have stabilized
detrimental shrinkage, expansion, or surface.
capillarity.

A3 Coarse material only, no binder. Portland
High internal friction, no cohesion, cement stabi-
no detrimental capillarity. lization.

Ah Silt soils without coarse material, Bituminous
and with no appreciable amount of stabilization
sticky clay. Internal friction
variable, no appreciable cohesion,
no elasticity, high capillarity.

Re uire addition

A5 Similar to Ad and in addition ochoarse materials.
possess elasticity in appreciable tuminous stabilaz-
amount. Dion.

A6 Clay soil without coarse materials. Mechanically stabi-
Low initial friction, cohesion high lézgdlinddchimically

s
in low moisture no elasticity. caIcIunghlngHe.

A7 Similar to group A6 but possesses Same as in 5.
elasticity also.

A8 Very 30ft peak and muCh incapable Telford foundation.

of supporting a road surface. Low
internal friction, low cohesion,
apt to possess capillarity and
elasticity in detrimental amount.

182

Although the decision to construct any particular type

of road will depend on the actual survey and tests, broad
recommendations can be made for various parts of Pakistan
on the basis of predominant soil types, climatic condi-
tions, and the availability of materials. These should,
however, be considered as essentially tentative until
more information is available from practical tests under

local conditions.

EASTERN PAKISTAN

The soil in greater part of Eastern Pakistan is clay
loam, becoming hilly in the eastern section. The temper-
ature is moderate, but the rainfall is excessive, the
average being 80"-90" in a year. The type of road best
suited is bitumen stabilized, as it is impervious and
helps to keep the soil from being washed away. Bitumen
is easily available from the coal-fields in eastern

Pakistan.

PUNJAB

Punjab is one vast alluvial plain. The greater part
is good loam. The summer is hot, the maximum temperature
being near about llO°F-115°F in shade. The total precip-
itation in Northern parts is 24 inches and in western part
10 inches. The types of roads recommended in this province
are cement stabilized for western part and calcium chloride

or sodium chloride stabilized in Northern part.

183

SIND

The‘soil in Sind ranges from sandy to loam. Some
portions are.reported to contain heavy concentration of
sodium chloride and other salts. The average annual
precipitation is 6.3 inches. The temperature during win-
ter is moderate but in summer it is very high -- in most
parts about 115-120°F. Soil from saline areas may be
used to stabilize surfaces in other parts as such soil
may help to maintain the moisture content. In most part

portland cement stabilization will be found advantageous.

NORTHWESTERN FRONTIER PROVINCE

Northwestern Frontier Province and the tribal agency
are mainly mountainous and sandy with the exception of
Peshawar and Mardan districts and portions of adjoining
districts which are river intracts of Indus. The latter
consist mostly of good loam. The climate varies in hill
and plain districts. The hilly areas have very severe
cold in winter and are subject to frost. Stone roads would
provide the cheapest surfaces in hilly areas. In sandy
areas cement stabilized roads would be most serviceable.
During summer the heat is intense; the temperature in shade
being 110-12OOF. The precipitation is low, amounting to
a total of 15 inches or thereabout in the year. The soil
becomes very dry in summer. In plain areas where the soil
is loam, bitumen and cement stabilized roads can be made
with advantage. Bituminous materials could be obtained

from the coal fields which are being developed in N.W.F.P.

184

and cement is easily obtainable from the adjoining dis-
tricts in Punjab.

BALAUCHISTAN

Balauchistan is one vast expanse of rugged, barren,-
sunburnt mountainous area, rent by high chasms and gorges,
alternating with arid deserts and stony plains. In places
it is redeemed by level valleys in which the soil is
slightly sandy loam. The rainfall is irregular and scanty,
ranging from 3 to 4 inches. The heat during summer is
intense, the temperature going up to 120°F in shade. In
higher altitudes the heat is less, but the winters are
severe and heavy snowfall is experienced. Stone and gravel
roads in hilly areas are recommended. Cement and bitumen
stabilization can be employed in plain areas.
The success of road construction work will depend on the
amount of planning behind such projects. Careful experi-
mentation for the determination of the most suitable types
for each area and work on local problems is a prerequisite
to such planning. The establishment of at least two
central research laboratories, one in Eastern Pakistan and
the other in Western Pakistan is therefore an immediate
necessity. The functions of these laboratories would
include:
(a) Survey of local conditions in areas under their

jurisdiction.
(b) Improving methods of design, construction methods

and procedures.

185

(c) Developing new materials for highway use.

(d) The collection and dissemination of technical data
and literature pertaining to outside research activi-
ties and construction practices.

(e) Advisory work.

(f) Training of field engineers in the theory and practice
of stabilization.

These laboratories should be supplemented by field
laboratories on the site of the actual construction project
under the supervision of trained laboratory assistants or
the engineer in charge of work.

The collection, organization and presentation of
research data requires a staff of competent investigators.
Such investigators must be efficiently trained in the funda-
mentals of research to insure the proper degree of expertness,
impartiality and precision in their work. The professional
staff should include the following:

(a) A civil engineer in charge of research, Specially
trained in highway engineering work.
(b) A research chemist, with a degree in chemical engin-
eering or chemistry.
(c) A physical research engineer, with special training
in physics and mathematics.
These two research units can be opened one at Iahore and the
other at Decca. The engineer in charge of each unit should at
least be an executive engineer with the other officers as

assistant engineers.

185

SUGGESTED READING

Agg. T. R.
1920 American Rural Highways. McGraw-Hill.-N. Y.

Alabama State Highway Department.
-l945 Soil Cement Typical Specifications. Roads and
Streets, 88, (10): 89-90.

American Association of State Highway Officials.
1945 New Design Standards for Secondary and Interstate
Highways. Roads and Streets, 88, (ll).

 

American Association of S. H. Officials.
1947 Standard Specification for Highway Materials
and Method of Sampling. 1220 National Press
Building, Washington, 4,D. C.

American Association for Testing Materials.

1944 Committee D-18 on Soils for Engineering Pur-
poses. Philadelphis, Pa. Procedures for test-
ing soils.

Belcher, J. Donand.
1941 A Field Investigation of Low-Cost Stabilized
Roads. Purdue Engineering Emperimehtal Station
Research series no. 81. Lafayette, Indiana.

Black. JO CO '
- 1957 Bituminous Stabilized Base Construction in
Missouri. Roads and Streets, 89, (2):. 29.

Bovey, C. F.
1958 Base Stabilization with Emulsified Asphalt.
Roads and Streets, 81, (7): 58.

Brown, V. J.

1955 Low Cost Roads and Brid es. Gillette Publishing
Co. _ZUO W. NadIson SE. CHicago, Illinois.

Brown, V. J.
1958 1 Short Course in Soil Stabilization. Roads
and Streets, 81, (2): 25, (5); 55, (4) 55, (5):
55, (12): 45.

Brown, V. J. .
1940 Plant Mix Soil Cement Base Course Over Blow Sand.
Roads and Streets. 85, (5): 57.

187

Burggraf, Fred
1955 Progress in Road Stabilization by Use of
CaClz. Roads and Stretts, 1g, (4).

Calcium Chloride Association.
1941 Soil Aggregate Stabilization and use of CaCl
for Military Roads and Airport runways. Dusging
laying, base stabilization surface consolidation,
with notes on the use of CaCl in concrete
work for Military use. Detro t, Michigan.
Bull. No. 26, pp. 29.

Calcium Chloride Association, Detroit.
1942 Surface consolidation and maintenance with
calcium chloride: for low cost roads and
base development.

Dent, H. G.
1940 Mobile Soil Laboratory, Roads and Streets,
85, (2): 54.

Dow Chemical Co.
1955 Improved low cost soil and gravel roads. The
Dow Chemical Company. Midland, Mich.

Dow Chemical Co.
1957 Laboratory Procedures of Dowflake road Stabilize»
tion department.

DOW 00 We '
1934 Methods and Cost of Stabilizing Gravel Roads
in Michigan County. Roads and Streets, 11, 151:
205.

Downey, B. R.
1945 Michigan Practice in Gravel Stabilization.
Roads and Streets, 8g, (6): 57.

Highway Research Board
1946 Soil Bituminous Roads. 2101 Constitution Ave.
Wash. 25 D. C. a

Hogentogler, C. A. (Jr.)
1955 Stabilization of Low Cost. Roads by Calcium
Chloride.Roads and Streets, 76, (10): 559.

Hogentogler, C. A.

1957 Engineering Preperties 23 Soil. McGraw-Hill
oo ompany, New or .

188

Hogentogler, c. A., and Willis, r. A.
1952 Present Trend of Subgrade Research. Proceedings
of the Highway Research Board.

Housel, W. S.

1958 'Experimental Soil-Cement stabilization at Che-
boygan, Michigan. Proceedings of the seventh
annual meeting of the Highway research board.
National Research Council. Washington D. C.

Kansas Highway Engineering Conference, Manhattan.

1946 Proceedings of Kansas Highway Engineering Con-
ference. Kansas State College of Agriculture
and Applied Science. Engineering Expt. Station.
Bulletin. V01 0 510

Kynnersley, T. R. S.
1946 Roads for India. Published for Tata San Limited
by Padma Publications Limited, Bombay. Laxme
Building, Sir Phirzsheh Mehta Road, Fort, Bombay.

League of Nations
1950 Advisory and Technical Committee for Communica-
tions and transit. Problems adopted by the
Committee at its 15th session. Genera.

Loth, J. M..
1940 Detail of Soil Stabilization with Emulsified
Asphalt. Public Works, 71, (10): 14-15, 58-59.

Mckesson C. L.
1921 Crushed Stones and Gravel Roads. Public Roads,
‘3, 111: 5.

Paula, J. I.

1954 A general Outline of the Construction of Low
Cost Bituminous Roads. Roads and Streets, 11,
(4): 1290
Permanent Internation Association of Road Congress.
1950 Sixth Con ress Re ort. Association Office 1,
Avenue E'Iena, ParIs.
Portland Cement Association.
1942 Soil Cement Road: Construction handbook 5rd

edition Chicago, Illinois, Portland Cement Association

Portland Cement Association.
1946 Soil Cement Mixtures, Laboratory Handbook.
2nd ed. P. C. Association. Chicago, Illinois.

Stanton, T. E., and Haveem, F. W.
1954 Role of laboratory in the Preliminary Inves-
tigation and Control of Materials of Low Cost
Bituminous Pavements. Proceedings of the High-
way Research Board.

Walker, G. M.
1917 The Measure of Civilization. New York.

Weld, we E0
1920 India's Demand For Transportation. New York.
Thesis Columbia University.

 

1940 Earth roads in India. Civil Engineer London,
35: 4:120 ’

 

1944—— Determination of Cement Contents of Soil Cement
Mixtures. Public Roads, pg. ( ): 297.

Mar 27 '50 .
AP 2355 _ ‘ g;

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