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THE EFFECT OF ADMIXTURES
ON THE FREEZING POINT OF A SUBGRADE

Thesis far HM Degree of I. S.
MK‘HIGAN STATE COLLEGE
E. I. Windowski—M. W. Hichoh

1949

 

The Effect of Admixtures on the

Freezing Point of a Subgrade

A Thesis Submitted to

The Faculty of
MICHIGAN SEATE COLLEGE
of

AGRICULTURE AND AIPLIED SCIENCE
By
E. R. Lewandowski M. W. Nichols
Candidates ror the Degree of

bachelor of Science

June 1949

THESIS

25-7603

TABLE OF CONTENTS

Introduction

Theory and Background

Description of Technique and Equipment
Procedure

Results

Discussion of Results

Conclusions

Bibliography

030110!“

16
19
21

INTROUCTION

Most persons living in the northern section of
the United States or in a location with a similar climate
and who drive motor vehicles are well aware or the
havoc that may be wrought on highways as a result of
frost action. Some roads are broken up quite a bit,
Others are affected little. Gravel roads and roads
with bituminous surfaces are usually affected greater
than concrete highways. The reason for this will be
shown later. Particular sections of a road surface may
be raised an amount up to six inches due to frost action.
Usually the surface breaks up if the heave is greater than
one and one-half inches to two inches. The heaving is due
to ground water freezing and expanding. The use of admix-
tures to reduce the freezing point will consequently reduce
the amount of frost action. It is the purpose of this
paper to show what admixtures will lower the freezing
point the greatest and how they react to frost action

when finally frozen.

THEORY

Frost heave is due to the freezing and subsequent
eXpansion of moisture in the soil. The freezing forms
layers of ice caused by the growth of ice crystals
in the direction of heat transfer. The layers of ice
sometimes form in the shape of lenses, hence the term
ice lenses. The ice crystals in growing exert pressure
on the particles around them and since there is less
resistance above, the soil begins to heave or erupt.

This eruption is often called a "frost boil." When the
frost "goes out" of the ground, the ice in the frost boil
turns to water and flows out of the frost boil, leaving

a void which has lettle supporting power. Damage to a road
surface is done both upon eruption of the surface and also
when a vehicle sinks in the void left by the frost boil.
The repair of a gravel road after such action has taken
place is not costly or involved, but when the frost action
takes place under a bituminous or concrete surface the
repair may prove to be costly.

There are various conditions Which are necessary
before frost heave can occur. These are:

(l) The soil must be saturated.

(2) The soil must have an ample supply of water within

itself or have a supply of water to draw on.

(3) The soil grains must be of size as to facilitate

"sucking-up" of water to the zone of freezing.

-2-

(4) There must be a formation of layers of ice.
The formation of these layers depends on
(a) The rate of temperature change.
(b) The moisture content of the soil before
freezing.
(c) Nearness of additional water.
(d) The rate at which capillary action takes
place.
(e) The density of the solution.
(f) Depth to ground water.
(g) Air dry water content.
(5) The ice crystals, in growing, must exert enough
pressure to cause heaving.
In addition, previous experiments have found that
the more colloidal material in the soil, the greater the danger
of heaving. Pulverzer-compacted clay has a greater amount
of heave than undisturbed clay. The most severe heaving of
clay occurs at a density of 102-107 pounds per cubic foot.
There is also much heave when the air dry water content is
between three and five percent. Lastly, a nonQuniform soil 7
results in a greater heave than a uniform soil.
In an experiment reported by A. W. Johnson,(1)the
relation of the texture of soil to the amount of frost

heave was given by the following table:

(1) "Frost action in Subgrades and Bases" A. W. Johnson

Roads and Bridges Sep. 1947 p. 104

-3-

Texture of Soil Height of Heave (inches)

Silt 6
Very fine sand and silt 5
Silty clay 5
Very fine sand 4
Sandy clay 3

The reason for the great height of heaving in silt
is the fact that silt has a high capillarity and therefore
contains a high degree of water. This water upon freezing,
increases its volume. Since the silt has the greatest
amount of water it will have the greatest amount of volume
change (or heave) upon freezing.

There have been attempts made to reduce the amount
of frost heave by completely eliminating the silt in a soil.
If this is impracticdl or impossible, a lessening of the
severity may be had by being certain of good drainage.
This would eliminate the supply of water, one or the
conditions necessary for frost action. Another remedy
may be through the use of admixtures in the subgrade.
These admixtures combine with the water to form a
solution which is more dense than just plain water. This
increase in the density of the solution lowers the
freezing point and the vapor pressure and increases
the surface tension and the viscosity. The lowering of the
freezing point leasens the severity of the frost heaving.
This paper deals with certain admixtures, why they are used,

and results obtained from using them.

-4-

Some of the admixtures currently used in soil stabilization

are ammonium chloride, sodium nitrate, sodium chloride, calciuni
Chloride, pctassium carbonate, potassium dihydrogen phos-
phate, limestone dust, tar (TC), emulsified asphalt (AESGl)

and liquid aSphalt (MC-1). Due to the shortage of time,

samples were only tested whicn contained as admixtures sodium
chloride, calcium chloride, lime, and emulsified asphalt.

These were picked because they are most commonly used now in

stabilization practice and they are both plentiful and economical

-43-

Dgscription Of Equipment And Technique

In performing the research for this thesis, soils
representing the worst possible soil conditions and the
best possible soil conditions were used. A sample consisting
of 100% silt was used to represent the worst condition. A
sample consisting of 7.5% silt, 15% clay, and 77.5% sand,
'was used to represent an ideal road sub_base sample. It
would have been much better to have used several samples
of different combinations but the limited length of time
in which to perform the experiment made it implausible to
use more than the two samples.

The admixtures used were ones that are economical and
easily obtained. The percentages of the admixtures used
were based on what has already been economically used in
soil stabilization practice. The following admixtures

were used in the percentages shown:

Calcium Chloride ---------- 1% (Ideal sample)
n ---------- 2% (Silt)
Sodium.Chloride ----------- 1% (Ideal sample)

" " ---------- - 1% (Silt)
Crushed Limestone --------- 50% (Ideal sample)
” " -------- 50% (Silt)
Emulsified Asphalt -------- 5% (Ideal sample)
" n -------- 5% (Silt)

Sodium Chloride ----------- 10% (Ideal sample)

(5)

Procedure

 

The first step was to obtain the soil samples. Boichot
2DS sand was used. The clay was obtained from the excavation
for Robert Shaw Hall and the silt was obtained from the
college gravel pit. The soil samples were dried with a
Brunsen burner and the ideal sample was prepared using the
percentages by weight as previously mentioned. A compaction
curve (Proctor) was made for both the silt and the ideal
mixture to determine the percentage of water contained by
the soil when it had reached its maximum density. The dry
density of each sample was also obtained.

To make samples of a convenient size for these experiments
round, waxed, one pint, card board containers were obtained.
The soil was mixed with the proper percentage of water so
that it would be at its maximum.density and then mixed
with the proper percentage of admixture. Two samples each
of silt and ideal soil were made with no admixture and
six samples using each admixture for both silt and ideal
soil were made. The mixtures were firmly packed in the
containers by filling the containers in increments of
one third and tamping twenty five thmes. Ten or twelve
holes were punched in the bottom of each container.
zhe samples were then set in a large pan containing
enough water to cover the holes. The silt samples, which

have fast capillarity, were left in the water seven days

(6)

and the ideal soils were left in the water for at least

ten days. The samples were then placed in a freezing chamber
and subjected to temperatures varying from.thirty two.
degrees Fahrenheit downward in increments of one degree.

As each sample froze it was removed from.the freezer

and broken to see if frost lenses or crystals had yet

been formed. If lenses or crystals had been formed the
temperature was recorded and the sample photographed.

The samples were left in the freezer for at least one

day before being broken.

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Test'Results

Ice Formation
100$ Silt Igeal Soil

_§reezingTemperature
100% Silt Ideal Soil

Description of
Adlai}: tur e

Rene 5 30 Large Large
Lenses rystals

1S Sodium 24 25 Very Small No Crystals

Chloride Lenses

10;? Sodium -— —o ______ No Crystals

Chloride

1% Calcium -— 24 _"_____. Very Small

Chloride Crystals

2% Calcium 25 -- Very Small ______

Chloride Lenses

50% Crushed 24 24 No Lenses No Crystals

Limestone

5% Emulsified 25, 24 Very Small Very Small

ASphalt

(10)

Lenses Crystals

    
     

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100% Silt, No admixture

o
Froze at 51 F, large ice lense
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Ideal Soil, fio'admixture
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Froze at 50 F, large ice crystals

-11-

 

100% Silt, 1; Sodium chloride
0

Froze at 24 F, Small ice lenses

K -- (’5- ' ‘

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Ideal Soil, 1% Sodium chloride
0
Froze at 23 F, small ice crystals

-12-

 

100% Silt 2% Calcium chloride
0
Froze at 23 F, Small ice lenses

   

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Ideal Soil, l%*dafcium chloride
0
Froze at 24 F, Small ice crystals

-13..

 

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100% Silt 50% Crushed limestone
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Froze at 2d F, No ice lenses

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Ideal Soil, 50%*Crushed limestone
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FrozeFat 240?, No ice crystals

-14-

 

 

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100% Silt, 5% Emulsified Asphalt
0
Froze at 25 ”1 ice lenses,

 

‘ K

 

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Froze at 24 F, Small ice crystals

-15..

 

Ideal Soil, 10% Sodium chloride
0

Froze at-—C>F, No ice crystals

-15a-

Interpretation of Results

The results obtained were very satisfactory. All of the
admixtures used lowered the freezing point of the sample
below the lowest temperature to be expected, 26 degrees
Fahrenheit.

With no admixture present, the sample containing 100%
silt froze at 51 degrees Fahrenheit, one degree below the
freezing point of water. Due to the high capillarity,

a large volume of water was present. This volume was so
large that the sample froze at almost the same temperature
as water. Also due to the large amount of water held in
capillary action was the formation of ice lenses. Since
this soil froze at the highest temperature it can be seen
that it would be the most unsatisfactory for a subgrade.
Due to the ice lenses formed, it can also be seen that a
subgrade containing silt would have the most frost heave
due to volume change.

The ideal soil containing no admixture froze at 50
degrees Fahrenheit with the formation of no ice lenses
but with the formation of large ice crystals. Thus, a
subgrade of this material would be unsatisfactory since
it freezes at a relatively high temperature with the
formation of ice crystals.

The samples containing admixtures froze below 88 degrees
Fahrenheit, the lowest soil temperature that is apt to be

encountered in a subgrade. This indicates that a subgrade

(l6)

that a subgrade containing any of the admix ures would
result in a subgrade that would not freeze, and subsequently,
have no icd lenses.

The test sample containing 5% emulsified asphalt in silt
froze at 25 degrees Fahrenheit with the formation of
ice lenses so small as to be barely discernable. The
emulsified asphalt evidently broke up the capillary action
of the silt to a great extent. Frost heave in a road having
a subgrade of silt treated with emulsified asphalt would
be negligible since the volume change due to the formation
of the tiny lenses would be negligible. The same result
was found in the ideal soil sample which froze at 24 degrees
Fahrenheit. Very small crystals were found which would
cause very little volume change. The freezing point was
1 degree lower than that of the sample containing silt
since silt has a greater capillarity and therefor a
greater amount of_water.

The silt sample with 50% crushed limestone froze at
24;iegrees Fahrenheit with the formation of no ice lenses.
l e ideal soil sample containing 50% crushed limestone
also froze at 24 degrees Fahrenheit with no formation of
ice lenses or crystals. A subgrade containing this admixture
would therefore have no frost heave due to the formation
of ice lenses and crystals.

Silt containing 2% calcium chloride froze at 25 degrees
Fahrenheit, the lowest temperature recorded for a silt
sample. Hence, from.the standpoint of the lowest freezing

(l7)

temperature, the best admixture to use with silt would

be calcium chloride. Small lenses were formed, however,
and therefore there would be a slight heave upon freezing.
The soil sample with 1% of this admixture froze at 2% degrees
Fahrenheit, one degree higher than the silt sam le.
This is adnorma since all the other samples tes
the silt samples froze before the ideal soil samples,
however, this could have been due in part to the extra
lfl of the admixture present in the silt. Small ice
crystals were formed and hence a small vol1ne change would
occur upon freezing.

Silt containing lfl sodium chloride froze at 24 degrees
Fahrenheit with the formation of very small ice lenses.
The ice lenses were so small as to present little volume
chaLge. The Ideal soil sample froze at 23 degrees Fahrenheit,
the lowest temperature reccrded for the regular samples.
The onLy sample with a lower freezing point was the soil
sample containing 10% sodium.chloride, an impractical mix.
This sample froze at—CD degrees Fahrenheit. From the
standpoint of the lo est freezing point it may be concluded
that a 1% soduum chloride mixture would’be the best for
a subgrade. Since there were no ice crfstals or lenses
formed, this admixture would also be best from the standpoint
of volume change and subsequent frost heave.

The ideal soil sample containing 10% sodium chloride
froze at HO degrees Fahrenheit with the formation of no ice
crystals or lenses. As was before stated, this was an
impractical mix and was used purely for experimental purposes.

(18)

CONCLUSION

From the results obtained, several conclusions con
be drawn:

(1) A subgrade composed of silt will freeze sooner
than a subgrade of ideal soil containing 7.5% clay, 15%
silt, and 77.5% sand.

(2) Since ice lenses are more detremental than ice
crystals, a subgrade containing silt will heave greater than
one or ideal soil.

(3) A silt subgrade containing 2% calcium chloride as
an admixture would have the lowest freezing point.

(4) A silt subgrade containing 50% limestone would
have the least amount of heave due to ice formation.

(5) A 1% sodium chloride admixture in ideal soil would
lower the freezing point the greatest.

(6) An ideal soil would have no heave due to ice
formation if the admixture used was either cnushed limeStone
or sodium chloride.

(7) Using current prices (May 16, 1949), and quantities
as indicated prev10usly, the most economical admixture that
could be used is sodium chloride.

grices as of May 16,41949

Sodium chloride a 9.50 per ton
Calcium Chloride $23.36 per ton
Crushed Limestone $35.50 per ton
Emulsified A5phalt g .11 per gallon

-19-

Based on the foregoing conclusions, the authors recom-
mend the use of sodium chloride as the admixture which will
be the most effective in the prevention of frost heave with
regards to lowest freezing temperature, least formation of ice
lenses and crystals, and lowest unit cost.

There is still much to be done along the lines of this
experiment. Many of the admixtures listed in the text of
this thesis could not be tested due to the lack of time. A
check should be made on the results by performing an experiment
determining volume changes upon freezing using the various
admixtures. Only two different soil types were used where
as it is known there are many more in existence. Various
percent ages of the admixtures should have been used in deter-
mining the most effective from the standpoint of frost heave.
Therefore, while the authors hepe they have contributed some-
thing to the knowledge of the effect of admixtures on frost
heave, there is a large extensive prograi which must be carried

out before the problem of frost heave can finally be overcome.

-20-

lO.

Bibliogranhy

"Controlling Frost Break Up," American City, Vol. 57,
p. 15 (1919)

"Preventing Frost Damage in City Streets," American
Clix, Vol. 58, p. 11 (Jan. 1943).

"Sand Cushions to Eliminate Frost Heave“, Roads and
Streets, Vol. 77, p. 405-6 (Nov. 1954).

MILLER, H. H. & SMITH, D. M., "Theory of Frost Heave
and Use of Dow Chemicals," Roads anr Streets, Vol. 77,
p. 219-91 (June 1934).

"Prevention of Frost Heave," Roads and Streets, Vol. 77,
p. 201-10 (May 1954).

BURTON, V. R. & BEHKELMAN, A. C., "Results of Field
Studies on Frost Heave," Roads and Streets, Vol. 71,
p. 272-6 (July 1951)

HENDERSON, E. A. & SPENCER, W. T., Effects of Subgrade
Treatments on Pavement Faulting and Pumping," EQ§§§_
and Bridges, Vol. , p. 85 (April 1947).

MILLER, H. H. & SMITH, D. M., "Methods for Prevention
of Road Failure Due to Frost," Roads and Streets,

Vol. 77, p. 919 (June 1954).

"Salt Roads,fl Scientific American, Vol. 167, p. 26
(Jury 1942).

JOHNSON, A. W., "Frost Action in Subgrades and Bases,"

Roads and Bridges, Vol. 85, p. 104 (Sep. 1947).

Bibliogranhy

ll. SMITH, H. J., "Frost Damage to Sealed Surfaces,"
Roads and Bridges, Vol. 85, p. 110 (Aug. 1997).
2. DOCKERY, W. D. & HAIIGAULT, D. E. H., "Soil Stabilization
- Lime,“ Roads and Str,ets, Vol. 90, p. 91 (Aug. 1997).
13. BATEHAR, J. H., ‘H‘ghway Engineering," John Wiley &
Sons, Inc., New York, 1948.
14. TAILOR, D. H., "Fundamentals of Soil mechanics,"

John Riley & Sons, Inc., New York, 1948.

 

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