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THESIS
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BACHELOR 0E SCIENCE
DEGREE

IN ENGINEERING

BY
ABDUL HAMEED KHAN. B. A.

Theory of Air Entrainment

A Thesis Submitted to
The Faculty of

MICHIGAN STATE COLLEGE
of

AGRICULTURE.AND APPLIED SCIENCE

by

Abdul Hameed Khan
Candidate for the Degree of
Bachelor of Science

1948

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THESIS

 

 

 

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St wart Field Demonstrates Use of Air Entrainment

XI BIBLIOGJAEEY

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E‘e purpose of this thesis was to accumulate all the
_important information of the past related to the entrain-
ment of’air in concrete. As the study of air entrainment
is a relatively new subject, most of the work done on it
is scattered in the various Engineering publications issued
at different times and thus uncoordinated. She author has
tried to collect this scattered information and to give a
complete picture of air entrainment so as to be of use to
the Engineer and layman.

The improvements obtained through the use of air
entraining concrete over that of plain concrete are durability,
workability, density. resistance to scaling, and kick of
segregation of the concrete irgredientsfiindicate the important
part they are going to play in the science of concrete in
the future. The detrimental pr0perties of the air entrain-
ing agents results in the lowering of strength, as will be
discussed later. This can be eliminated, to a large extent,
by the introduction of air at its Optimum limit and by the

reduction of water cement ratio.

I THEOJY OF AIR EJTRAIHLLNT

(a) and its effect on preperties of concrete
(b) Optimum air content

Page 1

TflnOnY OF AIR EJTRAINKEHT

Air entrainment is the process of purposeful intro-
cudtion of a definite quantity of air into the concrete
anxture in excess of that normally found in standard con-
crete. This additional air unlike the air in plain concrete,
must however exist in the form of minute, disconnected
bubbles uniformly distributed throughout the concrete mass.

Concrete mixtures posses naturally a high coefficient
.3; friction Which is lessened rather inefficiently by
cement water paste. Neither angular grains of cement nor
the water have a lubricating value. The Quantity gf_wa£gg
is limited due to the adverse effect of excess water on
strength, cohesion and durability. The guantity of cement
used is limited by factor of economy, heat generation and
columetric stability. Cement is generally used in excess
to increase plasticity which is detrimental to concrete
and a poor source
fipheroide

Spheroids are added aggregates. The deve10pment of
foam in concrete mixtures provides alubricant of high
value. The effective spheroids of air range in size of
_i_J_o_._ _]:_§_ to 3194 _2_g §_i__e_‘g_e_ _s__i_§_e_. They constitute an added
aggregate in the mixture possessing complete flexibility
9.: am-

The introduction of spheroids reduces the internal
friction of“the concrete mixture and it allows the ingre-
dients to move and arrange easily with respect to each

-2-

other. The foaming action of an admixture causing the
spheroids has thus a great lubricant value and avoids the
need of using excess cement to accomplish this purpose.
Thus cement is allowed to perform its main mission of coat-
ing and cementing the rigid aggregate particles. The need
for using water as a lubricant is also eliminated.
Agglfintrainment Supports DensityTheory

The reduction.of water (of convenience evaporable and
migratory) gives us greater concrete density. Purposeful
air entrainment achieves this best so it confbrms to the
above theory.

Introduction of air (an extra fine aggregate of zero
coefficient of friction) results in lessened need for the
rigid fine aggregates in about the same volumetric pro-
portion. The use of air entraining agents should thus be
accompanied by a mandatory corresponding reduction in the
quantity of sand to avoid "over sanded" mixture.

The combined effect of the reduction in water (0.5-1.0
gal./bag of cement) and of’rigid fine aggregate results in
a mixture more resistant to the future migration of water.
These epheroids also serve as pressure relief (due to
hydrostatic pressure or crystal growth).

The effect of the air entraining admixture on concrete
according to Wuerfel is a function of the amount and
condition of the air entrained i.e., number, size and
degree of distribution of the bubbles of air in the mortar
component of the mixture rather than.on.total volume.

-5-

The chemical effect of these admixtures appears to be
limited entirely to the possible presence of types of
other than sudsing compounds, such as accelerators, deflec-
uletors, or gas-generating agents. Taking only the sudsing
agent, the effect of entrained air is cumulative, as
indicated below:

a. The entrained air acts as a very plastic and
stable non-reactive fine aggregate of high lubricating
value.

b. Its presence permits a marked reduction in water
cement ratio necessary to produce the desired placeability
of the mixture and

c. a reduction in the sand total aggregate ratio
normally required by approx. 1.3 times the amount of air
entrained: thereby reducing the total surface area of
rigid aggregate to be coated and lubricated by the cement-
water paste.

d. Reduction in W/C° effects a basic increase in the
strength and durability of the cementing medium, and
the reduction in the total water present in the mixture
reduces the amount of excess water available for formation
of channels through the matrix of the concrete; thereby
reducing permeability and bleeding.

9. Reduction in bleeding is increased beyond that
affected simply by reduced W/O by immobilization of
additional water through adsorption on the air bubbles.
Reduction in bleeding results in diminished separation

-4-
°Water-cement ratio_

of the matrix fronithe under side of coarse aggregate
particles and in diminished floatation upward of laitance.

f. Finally the numerous well dispersed air voids
provide reservoirs for the relief of pressure created in
concrete caused by temperature change and by the expansion
accompanying the transition of’water to ice. his contri-
bution to durability is reinforced by the reduced w/c and
lack of channelization of the matrix due to bleeding.

The entrained air is more closely related to the fine
aggregate than to any other component therefore the Optimum
percentage of air entrained should be a function of the
quantity Of fine aggregates in the mixture rather than a
fixed percentage of the total mixture.

Behaviour offfintrained A25.

The presence of the numerous well dispersed air bubbles
tends to immobilize the missing water through absorption
of the air bubbles and by interrupting the continuity of
the water channels or capilleries, Which have a tendency
to form through displacement or readjustment of the
ingredients in the fresh concrete during placement. This
fact reduces the bleeding or water gain.

As the water cement ratio is reduced the durability is
increased and the closing of the water channels results in
greater imperviousness. These air voids relieve the
pressures caused by thermal volume changes and expansion

of water turning to ice.

thimum Air Content

The Optimum air content is considered to be §;§ percent
by volume computed on the basis of the theoretical weight
of air free concrete of the same prOportion. This is
air content at which it has been.shown, that with the gain
in the scale resistance and durability by the air entrained
concrete,there would be no serious loss in flexural or
compressive strength.
Unit Weight of Concrete

The increase in the volune of voids ratio from that
l to 1.5 0/0 (normally) to 3 to 6 percent results in a

decrease of Z to 6‘pounds per cubic foot in unit weight

 

of concrete.

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ALTEODS USLID FOR AIR El-ITIR--IlL‘.Z;£LETl‘ III COECRETE

air entraining admixture

air entraining Portland cement

compound air entraining admixture

natural cements with air entraining materials

nhTHODS OF AIR neraxlwnmur 1H COECiJTE

Air is entrained in.concrete by adding materials to
the missing water which reduces its surface tension, caus-
ing it to foam easily and consequently entraining air under
the mechanical agitation of the mixer.

There are four methods of entraining air in concrete
which are discussed in detail as follows:

1. Air entraining admixture

2. Air entraining P. O.

5. Compound air entraining admixture

4. Natural cements with air entraining material

The above mentioned mechanisms whereby air can be
entrained in concrete are not the only one, and some peeple
contend as to their being the most satisfactory. Aluminum
and hygrogen peroxide have been used to incorporate air or
rather hydrogen.and oxygen, respectively, in concrete mixes.
These function by generating the gases instead of reaction
with constituents of the cement. They bear no relation to
surface tension reducing compounds.

There is still another method of introducing air
above the normal amount, into concrete and that is by use
of cement dispersing_agent. These are surface active
chemical compounds which are preferentially adsorbed by
cement, endowing the cement particles with electromatic
charges which make them mutually repellent. These compounds
do not lower the surface tension of water to a marked degree
and do not form stable anms with water alone, although

“8-

what they may do in a cement suSpension is something differ-
ent. They are not wetting or foaming agents and would not

be applicable to those uses of“wetting or foaming agent Which
depend on surface tension reduction. The mechanism whereby
they entrain air is evidently not the same as that of foam-
ing agents and is yet to be disclosed. It is suggested

that it is related to increased effective surface area of

the cement and the finer effective size of the cement
particles in the dispersed state.

In addition to the foregoing materials the ones listed
below have been used in.laboratory and in fields for the
purpose of air entraining.

1. Animal or vegetable fats and oils such as tallow
and olive oil and their fatty acids such as stearic and
oleic acids.

2. A commercial product known as Legro which consists
largely of oleic and resin acids.

3. Various walling agents such as the alkali salts
of sulfated and sulfonated organic compounds.

4. Water soluble soaps of resin acids and animal and
vegetable fatty acids.

5. M1301. materials such as the sodium salts of petro-
leum sulfonic acids, etc.

£§g;§ntreining in.Portland Cement

IThere are two types of Standard Portland cement now
available, to which a certain amount of air entraining
materials have been added at the mill. It is designated

-9-

types IA and IIA and is covered by American Society for
listing materials spec. Designation Cl75-46T.

The amount of air that the cement will entrain is
based on the amount of entraining material added at the
factory and the conditions of the mortar to achieve this
volume are specified. The air content of the mortar which
is tested and prepared in accordance with A. S. T. M.
method 0185-47T has to be 18 percent by volume with -3
percent toleranc e.

4Although the above mortar test is develoPed to give an
approx. ratio of 5:1 between the amount of air in the mortar
and in the concrete, but such relationship is very difficult
to be obtained.

CompoundéiggEntraining Admixtures

These compound air entraining agents are those which
besides their air entraining properties, contain various
types of accelerators and deflo-culators. The addition of
these materials serves to increase the strength and bond-
ing prOperties. These types of admixture is added at the
maxer.

Katural Cements with Air Entraininngaterials

Standard Portland Cement is sometimes mixed in the
ratio 5:1 to air entrained natural cements and it seems to
produce a satisfactory air-entrained concrete. The natural
air entrained in.natural cements must conform to the A. S.
T. M. epec. Clo-57 and also meet the mortar test for air

content stated above for air entraining Portland cement.

-10-

a. Air Bntraining Adnfixtures. Two Types.

Air entraining agents which have been successful are
of soapy nature. Their soapy action which is their natural
quality has nothing to do with any subsequent action with
the cement. neutralized Vinsol resin (NVX) and Darex are
examples of this type.

The other types of admixtures used as air entraining
agents are those which deve10p their foaming action, only
due to reaction with the hydroxides of the alkali metals
present in the cement. In this case the amount of air
entrainer produced is not preportional to the amounts of
these substances that are added, but also the amount and
availability of the natural alkali oxides that are present

in the cement. Resins; flake Vinsol resin, and the various

 

animal fats can be stated as examples of‘this type. Owing
to lack of consistency in the results obtained from these
types where the amount of air entrained is unduly affected
by the time of mixing, the use of these products is not
recommended.

There are many other substances which have the prOperties
of air entraining but unless the exact nature of their effect
on the quality of concrete has been proved through research
and experience their use is not encouraged.

Flake Vinsol resin obtained by selective extraction
from pine wood. It is composed chiefly of a mixture of
various resin acids which combine with alkali to form soaps.

Neutralized Vinsol resin (Sodium resinate) is made by

-11-

treating the resin with co mercial sodium hydroxide (caustic
soda).

Darex (Aha) is a triethanolamine salt of a sulphonated
hydrocarbon. (Further discussion follows at the end of this

paper and is under the heading of "Supplementary Totes").

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‘ ;..in in the trio nethods

;here is no great comparative c
of using admixtures, i. e., that of mixing it with the

cement or mixing it at the mixer with the batch. It is

left to the engineer whichever method of control he uishes

to chose. The results would be satisfactory if proger
control has been exercised.

The amount of air entraining material serves as a
control when mixed at the mixer if the mix has been
established.

In case of air entraining cements, the amount of air
entraining material is fixed but if required, more of it
can be added in the mixer in case of deficiency, and so
can the cement ratio be increased.

This additibnal use of admixtures to meet a deficiency
is done either mechanically by means of an automatic dis-
pensing device or manually handled. ” solution of admixture
with water is kept ready and must be enough to last for
one day's pour. This solution must be protected against
freezing in winter and the container kept clean at all times.

From the point of view of work in the field, it would
appear that a more uniform quality of concrete is likely
to be produced by using air entraining Portland cement,

than by adding the very small quantities of air entraining

agent s dur ing mixing .

IV redress AFFJCTInG AIR COhTsNT
Type and grading of aggregate

a.
b.
Ce
d.
e.
f.

g.
h.
i.
j.
k.

affect
Effect
Effect
affect
affect
Vinsol
affect
Effect
Effect
Effect
Effect

of sand percentage

of coarse aggregate

of amount and brand of cement
of amount of agent

of ratio of sodium hydroxide to
resin

of’consistency

of mixing time

of temperature

of vibration

of depth of concrete

-15-

LLi COJTJJLJT AE‘B‘LJCTI;:G FACTUELS

The amount of air entrained in concrete has to be
kept at the Optimum limit in order to get the best results
from air entrainnent, therefore the proper design of the
mix to achieve this desired air is of ultimate importance.
All factors affecting the air content have to be carefully
considered, sepecially the effect of W/C ratio which will
be very'marked in lean mixes than in rich mixes.

The amount, type and grading of the aggregates, type
and quantity of cement, mixing time, method of mixing,
temperature, amount and type of air entraining admixture,
all have a great effect on the QQantity of air entrained
in the mix.

Type and Grading_offiAggregate

Consideration must be given to the nature of the
aggregates in determining the amount of air entrained. It
has been found that concrete made with crushed gtgpg or
slag will contain about 1 percent more air than comparable
concrete made with roundedggravel. This can be accounted
by the fact that more sand is needed when crushed stone is
used (Fig. 9) (Cordon).

The data used by Walker and Bloem for concrete using
two different Vinsol resin solutions are shown in Fig. 5.

Only a few tests have been made on coarse aggregate,
but the limited data available indicate that the coarse
aggregate has little effect, except insofar as it affects

-16...

the amount of sand required. (Bloem and Walker).
Effect of Percentage of Sand on Air Content of Concretg.

(Vinsol resin added at the mixer in solution.with NaOH,
43 parts water by wt. used for exp.)

Experiments run by M. G. Gonnerman.show that a reduction
in the percentage of sand in a mix caused the air content to
decrease. Reducing the sand percentage from 40 to 22 per-
cent decreased the air content as much as 1% percentage
points, the amount of reduction depending upon the presence
or absence of Vinsol resin in the mix. The rate of decrease
of air content with reduction in percentage of sand was
slightly higher when Vinsol resin was used in the mix. The
results of the experiments also show that a reduction in
sand percentage can largely offset the reduction in flexurel
and compressive strength that occurs when the same percentage
of sand is used with the air entraining addition as with
the concrete without addition. It is also observed that by
ggducingthe_percentage of sand when the air entraining
addition is used, the strength can be maintained at approxi-
ggtglg the same level as those fogfthe concrete without the
admixture.

The Effect of Coarse Aggregate on A1; Content.

As the size of the coarse aggregate used in concrete
increases the optimum quantity of total air in the mixture
is reduced. From data available (by Wuerpel) the air
content of the mortar and the overall benefit to the concrete
can be maintained about equal, when the total air content

-17-

is as Shown below for concrete containing various sizes of

coarse aggregate:

 

 

d. A. Max. size in inches Total Airjg
344 5.5
1 4.5
a 5.5
6 2.5

 

Amount and Type of Cement

The quantity of agent required to entrain.a.given
amount of air'is influenced by the type of cement, also a
smaller amount of agent is required for lean mixes than for
rich mixes. (Cordon Fig. 10).
Effect of Amount of Vinsol Resin on ii; Content of Concrete
“yixes with.Constant Cement Content.

It can be seen from the results of tests run by
Gonnerman that the amount of air entrained in a concrete
mix may be readily controlled by changing the percentage of
Vinsol resin added. The ability to control the amount of
entrained air by the percentage of Vinsol resin added in the
form of soap solution may at times be of considerable ad-
vantage since the air content for any given set of conditions
can be maintained at the desired amount by adjusting the
quantity of solution added to the batch. It has been observed
that .005 to .01 percent of Vinsol resin is required when
added in solution during mixing to markedly increase the
resistance of concrete to surface scaling and to freezing

and thawing.

Effect of fiatio of Sodium Hydroxide to Vinsol Resin in dig
Content.

It has been found that Vinsol resin is not very
effective in entraining air when added to the batch in
powdered form. Therefore, it generally is added in NaOH-
water solution and the discussion follows below.

fiesults of studies made by walker a Bloem indicate
the relationship of Sodium Hydroxide to Vinsol resin and
the effect of certain variation in their pr0portions on
the air content and compressive strength of concrete. It
is shown that air content is increased as the wt. of the
Sodium Hydroxide approaches the wt. of the Vinsol Resin.
Beyond that the material becomes less active, due to a
salting out action caused by the excessive amount of
Sodium Hydroxide (Fig. ).

Tests were made with solutions with the ratio of the
sodium hydroxide to the resin varied from 1.1 the usual
recommendation, to 5.0. The amount of Vinsol resin was
kept at 0.009 cercent of the cement. The results of the
data are shown in Fig. 8. It appears, for most of these
tests, the activity of the solution increased up to the
point where the weight of the sodium hgdroxide about equaled
that of the Vinsol resin used. Beyond this point the
solution was less active, probably due to a "salting out
action" caused by the excessive amount of the sodium hydroxide.
Consistency of the Mix

EXperience shows that the wet mixes entrain more air

-19-

than dry, stiff mixes. Therefore it is important to keep
this aSpect in view at all times and keep within reasonable
limits.

Effect of Mixing Time on Ai;quntent

There is no definite relation set up so between the
time of mixing and air content. It has however been shown
with the newer air entraining admixtures that the amount of
air content rises slightly during the first few minutes of
mixing time (5-12 min.) and then decreases with additional
mixing. The total amount of air entrained is also function
of the type of cement used.

Tests on the effect of mixing time on concrete carried
out by Walker & Bloem show that no differences in results
were found when three air entraining agents, 1. e. flake
Vinsol resin, sodium resinate (N.V.X.) and Darex were used.

The following is the table of results obtained:

 

 

 

 

Concrete without Concrete with
Mixing admixture admixture
time Cbmpressive Compressive Air
Strength Slump Strength Slump Content
6 98 97 94 95 94
12 . 100 100 100 100 100
50 98 74 . 96 74 86
90 98 55 101 . 55 58

 

Although the data are too few to draw conclusion still
it can be seen from the results of the slump tests, as well
as measurement of air content, that for this mixer, 12 minutes
were the adequate time of mixing. After this, both slump
and air entrained were decreased by additional mixing.

Effect of Temperature of the Concrete on Air Content.

It has been Shown by experiments that the amount of air
entrained decreases as the temperature of the concrete rises.
Figs. 6 and 7 show results of tests made by Messrs. Stan
Walker and Delmar Bloem on concrete using Vinsol resin,
sodium resinate and Darex as admixtures. By controlling
the temperature of the ingredients, concrete was mixed
which had temperatures after mixing, ranging from 46 to
106°F. It can be seen from Fig. 6 that in each admixture
the amount of air entrained decreased as the temperature of
the concrete increased. Fig. 7 shows the amount of air as
a percentage of the amount at 70°F. It is interesting to
note that inepite of using different admixtures and the
different amounts of air entrained by the quantities of
them used, all points fell on the same curve. The amount
of air entrained at 50°F. was 150 percent and at 100°F.,

77 percent of that to 70°F.
Effect of Vibration on Air Content.

Vibration causes a slight reduction in air content.
This is believed due to the compressive action of the solid
particles on the voids which are pushed upward. studies by
Wuerpel indicate that the apparent reduction in air content
by vibration is not sufficient to be reflected in the dura-
bility prOperties of the concrete.

The phenomenon of the reduction of entrained air due to
vibration is explained by C. E. Wuerpel who relates it to

the nature of the voids formed in plain concrete and in

-21-

purposedly entrained air. The air entrained in plain
concrete is present usually in large voids of sufficient
volume to develop enough buoyancy, causing a rapid upward
migration under the influence of vibration. There has been
little evidence of the buoyant force oi?the voids formed.
by the sudsing agents which are very minute and widely
spread, on the other large upward movement of air voids is
noticeable to naked eye in plain concrete under the influ-
ence of vibrations. The apparent reduction in air content
in.concrete with admixture may be attributed to the loss

of large bubbles of incidentally entrapped air typical of
plain concrete, which are also present in entrained concrete.
This reduction in apparent air content may be due partially
to shrinkage of the concrete, evaporation of moisture, and
by partial filling of some of'the air voids.

In spite of the fact that there is reduction in air
content due to vibration, the extent of the reduction is
not of an alarming nature as to affect beneficial prOperties
of concrete.

Effect og:pepth of Concrete on Air Content

Experiments by Walker & Bloem indicate that in high
sections of concrete containing entrained air, there is
apparent movement of the air from the bottom to the tOp
section because the air is partially compressed due to
superimposed concrete.

Columns of 6 inches in diameter and 4 ft. in height
were molded for the eXperiments. The concrete was placed

-22-

in 12 in. "lifts" each of which was rodded 25 to 50 times

as required in molding 6x12" cylinders . After the concrete
had hardened, the column.was broken into four pieces and

the air content of these computed. There was a decrease

in the indicated amount of air with distance from the t0p

of the column. It appears that these differences were due
to the compression of the air due to the weight of the
superimposed concrete. This contradicts the statement made
by some writers that there is no movement of air from the

bottom to the top section for the method if placement used.

V.

EFFECTS OF EJTRAINLD AIR OR PfiOPfinTIES OF COHCEETE

3..
b.
Ce
d.
30
f.
6.
h.
i.
3.
k.

Strength, modulus of elasticity
Durability-~reaction to freeze and thaw
scale resistance

Bleeding (water gain)

Bonding properties between steel and concrete
Thermal prOperties

fiorkability

Uniformity of concrete

massive otructures

Use of colour pigments

Application of air entrained concrete

-24-

ETFnCT OF EJIRLINmD.AIR 3N THE SCREJGTH AJD DURABILITY’OF

hAfiDENED concnnrn

 

It has been feund that entrained air in the normal
amounts of 5 to 6 percent exercises a great effect on the
strength and durability of concrete.

It has been also experienced that the compressive
strengths have been increased up to dfi for lean mixes con-
taining less than 5 a/sacks per cubic yard, while ordinarily
each percentage increase in the amount of air in plain
concrete reduces the compressive strength by 5 to 4 percent
and flexural strength 2 to 5 percent. The above effect on
the mixes of the entrained air has not been definitely
understood.

Effect on btrength

 

It is shown by various experiments that tie flexural
strength of concrete is reduced from 2 percent to 5 percent
and the compressive strength from 5 to 4 percent for each
1 percent increase in the amount of air over that which
exists in plain concrete. These comparisons are based on
the fact that the amount of concrete used is the same and
that the percentage of sand and amount oifwater have been
reduced to the minimum to get satisfactory workability.

This shows a reduction of 12 percent in flexural strength
and 18 percent in compressive strength for concrete contain-

'lain concrete

\

I

..r'
A.

ing 6 percent of total air as congred with

containing 1 percent of air. Although this reduction in

-35-

strength has to be given consideration in design, get it
has been pointed out by the fly. hesearch BDCTd, that in
Bridge design, with the high factor of safety adOpted,
the strength deveIOped is far_higher than the minimum
:requirement, and the comparative gain in durability and
workability offset the 18° percent loss in crushing
strength.

The thickness of the slab may be increased if it does
not come up to the established value of mod. of rupture
of 550 lbs. per sq. inch at 14 days as the minimum require-
ment for flexural stren¢th.
Decrease in otrenCth with the Entrainment of Air. (Gordon)

The strength of the concrete decreases uniformly with
increases in air content of the fresh concrete as shown.by
Fig. 6. The decrease amounted to 125 psi. about 5» average
for each 5 of air entrained at const. water cement ratio by
weight. Also at W/C held constant as shown in Fig. 6a, the
same reduction in strength for each percent of air entrained
for the higher constant N/C .65 as for the lower constant
fl/C of .45. When the cement content is held constant, and
the water cement ratio is reduced through reduction in water
content as a result of the entrained air, the change in
strength for each percent of air is not constant and ranges
from a slight increase for mixes of low cement content to
about 20C psi. reduction for each percent of air for mixes
of high cement content. It is also observed that there is

little advantage keeping the cement content constant When

using more than 6 sacks per yard, since the reduction in
strength as the air increased is about the same as that
for content W/C.

Fig. 1 shows results of tests made by Messrs. halker
and Bloem of 7 and 28 day compressive strength S of concrete
containing 4.5, 5.5, and 6.5 sacks of cement per cu. yard.
Vinsol resin was added in amounts of 0, 0.005, 0.0.0, 0.015,
and 0.020 percent of the wt. of cement, resulting in air
contents up to about 9 percent. It will be seen.that for
the 5.5 and 6.5 sack concrete, strength was reduced as air
was entrained. For the lean mixes (4.5 sack) the strength
was slightly increased for air contents up to about 6 per-
cent. ihis beneficial effect on the lean mixes, it seems
reasonable to suppose, was due to the improvement.in work-
ability--in spite of the fact, that according to usual
standards, the air free mix.was workable.

For 5 percent added air, the percent change in strength
is as shown in the following table.

 

Cement sacks per

 

cu.jd. 7 6.33173 28 days
505 -12 -16
605 -17 '20

 

There is also a close relationship between the entrained
air and compressive strength reflect not only the effects
of the air but also of the water used which has to be re-
duced in order to achieve same consistency. The authors

and other writers have suggested that the air affects the
-27-

strength exactly as so much water. This gives a good basis
fer design purposes, although not being true.

Fig. 2 shows 28 days compressive strengths plotted in
relationship to the gallons of water plus air per sack of
cement. Curves derived by interpolation from the original
data, are shown for 0, 2, 4, 6, 8 percent of air. The
s10pes of these curves decrease as the percentage of air
increases.

Fig. 5 shows conventional water cement ratio strengths
relationship for the same data as used in Fig. 2. It may
be seen that concrete containing 4 percent air and having
a Specified strength can be obtained by reducing the water
cement ratio about 1 to 1% gallons per sack below that
required to produce the same strength in normal cement
concrete.

(Gordan)

a. When W/C is held constant, the compressive strength
of concrete would be reduced approximately 200 psi. for
each percent of air entrained in the fresh concrete by
Vinsol resin. (This value does not apply where accelerators
are used in.combination.with the air entraining agent.)

Fig. 6.

b. Where the cement content is kept constant the change
in strength ranges from practically no change for concrete
of low cement content to a reduction of around 200 psi. for
each percent of air entrained for concrete of high cement

content. Fig. 6a.

c. The modulus of elasticity of an average concrete
having the same water cement ratio and the same aggregate
grading, will be reduced approximately 105,000 psi. for
each percent of air entrained in the fresh concrete. Fig. 7.

d. The ratio is not significantly affected by the
entrainment of air.

Effect on Modulus of Elasticity

There is a decrease in the modulus of elasticity when
air entraining concrete is used. Fig. 7 shows the difference
in the decrease of mod. of elasticity when using different
aggregates. The slepes of'the regression lines correspond
with the average of all tests, and at the same water cement
ratio a loss of approximately 105,000 psi. static modulus
of elasticity for each percent of air entrained can be
expected for average concrete mixes.

According to Gonnerman there is a decrease in the
modulus of elasticity of about 3 percent for each percent-
age point increase in air content of the fresh concrete.
Effect 9:4Air Entrained Cement on the Resistance to Freez-
ing and Thawing Action.

The air entrained cement posses greater resistance to
freezing and thawing action.

Fig. 9b shows the effect of Vinsol resin on resistance
to freezing and of limestone sand concrete as the result of
eXperiment run by A. T. Goldbeck on limestone sand.

Fig. 4a shows results of tests by H. J. Gonnerman with
15 air entraining Portland cements, eight of the cements

-29-

were ground with .05 percent of beef tallow and five with
.05 percent Vinsol resin. Included in the tests were
normal Portland cements from the same plants that furnished
the air entraining products. It is clear from the curves
of durability tests that the cements ground with tallow

and Vinsol resin gaveequally good results. It is also clear
that when the air content was increased only a relatively
small amount over that of'the concretes made with the normal
Portland cements, a very great improvement in resistance to
freezing and thawing was obtained. This was indicated by
the low eXpansion, small reduction in modulus of elasticity
and low loss in weight for air contents slightly above
those obtained with the normal Portland cements which were
generally less than about 1 percent. Concretes having air
contents of about 3 percent (An increase of about 2 percent
over that of normal Bortland cement concrete) showed about
as good resistance as those with higher air contents. Air
contents in excess of about 5w (above Optimum limit) should
be avoided, because they are accompanied by a considerable
falling off in strength, without any compensating gain in
resistance to freezing and thawing.

Lffect o: fintrained Air on Scale hesistancg

 

It has been shown by so many experiments in.the
laboritories and observation in the field that entrained air
in concrete increases its resistance to scaling due to
chloride salts used for ice control and by frost action.

Following are some of the results of eXperiments on

-50-

accelated scaling studies conducted.

Photographs taken by Gonnerman showing the top surfaces
of typical slabs containing normal Portland cement and air
entrained Portland cements from eXperimental projects after
they had been Subjected to as many as 575 cycles of the
surface scaling test Speak very high of the Values of air
entrainment. The specimens containing the air entraining
Portland cements showed only slightly, if any scaling after
500 to 575 cycles of this severe test, whereas companion
Specimens without the air entraining addition showed serious
scaling after 40 to 75 cycles. These results are typical
of many others obtained during the past 10 years.
method ofdvaluating Durability.

The progressive drOp in dynamic modulus "E" is measured
after subjecting the Specimen to freezing and thawing action,
and is in terms of the number of freezing and thawing cycles.
A sonic apparatus is used for this purpose.

A radio frequency oscillator furnishes power to a
driving mechanism which in turn vibrates the speciman. A
radio loud Speaker adapted to this purpose and there is also
a pick up which receives the vibrations that are transmitted
from the Specimen, and pass them to a vacuum tube volt meter.
The voltmeter indicates the natural resonance of the concrete
by maximum deflection of the dial hand. The frequency at
which the dial is vibrating is shown on another dial. Knowe
ing the frequency and constants of a certain Specimen, the

dynamic modulus can be calculated by using the following

-31-

formula:
Edeflg
E: modulus of elasticity. r/sq. K: constant depending
on dimension of Specimen, mode of vibration and condition
of restraint.

d: specific gravity
N2: fundamental frequency cycles/sec.

Effect of Cement Content and Air'Emtraining Material on
Durability. (Wuerpel results).

Influence of Water Content on Durability. Figure .
Effect on Volume Changes.

Studies made by Wuerpel show that a change was brought
about in the normal shrinkage and expansion characteristics
of concrete by the use of air entraining agents.
Bulking_Effect

Bulking effect of the entrained air causes an increased
volume of concrete, so quantity of materials that produce
one cubic yard of concrete when normal cement is used will
yield more than that with air entraining cement. It is
necessary to compensate for this increase in yield by
adjusting the mix slightly so as to maintain the desired
cement content. because the entrained air greatly improves
workability characteristics and increases slump, the adjust-
ment of the mix Should be accomplished primarily by reduc-
ing the sand and water content.

Effect of Ai; Content on Durabiligy

Freezing and thawing action results in the loss in

-52-

weight, expansion of concrete and drop in modulus E.
The influence of air on these three factors is shown in
Fig. by Gonnerman.

Miscel. Factors

It has been.fbund that abnormal air contents improve
the durability of concrete containing either mediocre or
good limestone but there is no appreciable improvement
in durability When the concrete contains check aggregates.
Effect on Bleeding (Water Gain)

By using air entrained cement we can.reduce the amount
of water gain, generally called "bleeding".

Bonding Fraperties Between Concrete and steel

It has been Shown by the work of Wuerpel and P. C. A.
that the strength of bond between concrete and steel is
not materially affected by the use of air entraining
materials provided the mix is properly designed and con-
trolled, and the air content kept within 5 to 6 percent.
The data also indicate air entraining admixtures When used
in concrete having a cement content of 6-0 bags per cu. yd.
enables the concrete to achieve at least parity with plain
concrete.

Wuerpel also mentions that the introduction of'air
entraining agents of Optimum quantity in reinforced concrete
reduces the bond of concrete to steel by not greater than
10 percent, but the uniformity of the bond increased. This
advantage of greater uniforndty offsets completely the
Slight reduction in bond strength and on the whole the

-53-

reinforced concrete is benefited.
Thermal Properties

Experiments run by Wuerpel indicate that the presence
Of the distributed air voids in air entraining concrete
do not materially reduce the rate Of heat diffusion when
the amount of entrained air is within the Optimum limit.
Average thermal diffusivity values in sq. feet per hour
of concrete wdthout air entraining admixture was 0.055
and when the admixture was used became 0.054.

Effect on Workability. (Cordon)

The workability of the air entrained concrete is im-
proved as the amount Of air entrained increases. Due to
the increase of slump thereby permitting a reduction in
we er content as shown in Fig. 5 (Cordon). The workability
was found to be better than that Of the concrete of lower
air content as measured by "Power's remolding appartus"
where slump is held constant through reduction in cement
and water. Fig. 5 Shows that the workability Of a mix
made with natural aggregates and containing at air with a
1%" slump is about equal to that of a mix containing 1% air
with a 5" slump, even though the cement content has been
reduced.

Effect on Uniformity g£_Congpet§

Homogenueity is greatly increased by use Of air entrain-
ing agents in concrete.

Studies made by Kennedy bear out the fact that homo-
genueity is closely related to bleeding. The less bleeding

-54:-

tie more uniform.the concrete from tOp to bottom. is air
entrainment reduces bleeding, it is reasonable to believe
that homogenueity will be increased.
Air Entrainigg Concrete for Massive gtructures. (fluerpel).

Using air entraining ccmcrete in large concrete
structures employing lean mixtures and large size aggregates
(above 2" max. size) Huerpel has brought out interesting
information from lab. studies. The total amount of air
entrained can be less than.that in pavements due to re-
duction.of mortar content due to the presence of arge size
aggregates. It was also showm.that the total air content
of 2.7 percent in a lean concrete mix containing 6 inch
aggregate is comparable so far as the mortar constituent
is concerned to a total air content of 4.0 percent in a
pavement concrete containing 1% inch aggregates. The
procedure of finding the unit weight of mass concrete by
not screening should not be followed as it will give tron
results, because a considerable amount of entrained air
would be lost. a 2 cubic foot measure is reconnended to
find the unit weight.

air entrained concrete can be pumped with excellent
results and as good as standard concrete. There would
be a normal slump loss 1 to 2 incher per l,C00 ft. of pipe.
the avera

e slump at the mixer is 4 inches using 5-6 bag

D

‘* .-v' {‘7‘ a" w ' ~" VJ... ' w -" r. ' « r4" "' r. " “ ' v- :.- . 1
mixes. ine (aptlub through the nlpe oi Cdflardbe iiprovLs its

L

C“

workability compaction and release of the ilostic concrete

0

as it masses through the pipe. air content is not affected

.2

- ’35—

by pumping.

Basic; 0E nil a;;hllili; 0340; in

a. .amouht ..efmiiinQ rater

3. amount of sand

c. affect on yield

d. Quality of ingredients

3. moisture condition of tie a “rext'
f. addition of CaCl;

~\. , Hr»- - -— ~ :- - .m: -- . - .2 4. ,—.‘ —/-‘ -. . ~
J—J’Q a‘l:'A- ‘- A-£«. .-J--—..sJ——L-c—Lr.a.l-- b-'-‘|v'_..-—u

 

affect on Lining water heuuired

 

Changes in design of concrete have to be adogted when
air entraining agents are used inorder to arrive at comparable
strength values to those of ordinary concrete. The factor
that is given most consideration is the water reduction of
water and sand content.

Due to the introduction of air entraining agents, the
slump of a concrete mixture can be kept at a desired value,
in Spite of reducing the amount of water that was first
used to get that value. The reduction in water cement ratio
in turn causes an increase in strength, impermeability and
durability of the mortar and reduces the bleeding. The
water content of an average concrete mix may be reduced
apporx. 6 pounds per cu. yd. with rounded aggregate accord-
ing to Gordan, and 8 pounds per cu. yd. with angular aggre-
gate for each percent of air entrained. The ordinary practice
is to reduce the water content from s to 1 gallon per sack
of cement when air entraining concrete is used. Fig. 2
(Gordon).

According to walker and Bloem, the requirements of
mixing water are reduced as air is entrained. Fig. 4 shows
the amount which the mixing water may be reduced for different
cement contents, with the reduction eXpressed as a percentage
of the volume of'air entrained in a unit volume of_concrete.

The diagram shows that the reduction in mixing water

-58-

ranged, for the 4.5 sack concrete, from 74 percent of the
air; for the 2 percent of air to 48 percent for 8 percent
of air; fbr the 5.5 sack concrete, the range was from 52
percent to 32 percent; and for the 6.5 sack concrete from
35 to 23 percent. This indicates that as more air was
entrained it became progressively less efficient in reduc-
ing mixing water; also, the air was progressively less
efficient as the cement content was increased.

affect of_Samd Content on Air Entrainment.

The sand content can be generally reduced by approx.
in of weight of total aggregate for each percent increase
in entrained air up to at least Bfi without any appreciable
change in slump or workability. Fig. 4.

Each percent reduction in sand permits a 2-5 lb. per
cubic yard reduction in water in addition to that mentioned
before.

Effect of Air Content on Yield.

ihe increase in yield due to the using of entrained air
can be checked by reducing the sand content of the batch by
3 to 4 percent of the combined weight of the fine and coarse
aggregate, or 1 to 1.3 times the amount of air entrained.
The coarse aggregate should be reduced if there is‘a tend-

ency for the concrete mixture to become harsh.

finality of the Ingredients.

The type of aggregate used must be preperly controlled
as to quality; Air entrainment will not improve the qualities
of concrete in Which poor aggregate have been mixed. The
aggregate must be of medium or'good quality before any of
the benefits that are connected to the use of air entrain-
ment can be realized.
ioisture Condition of the Aggregate and Concrete.

It has been.found that aggregate whose pores were
saturated with moisture after being used in.the concrete
caused a decrease in the resistance of the Specimen to freeze
and thaw test, as compared to using aggregates Which £222.
in a relative dry condition before mixing. Therefore, it
is important that the water should be kept at the_minimum
in order to obtains relative impervious concrete.
égngntrainment with Calcium Chggride.

It has been.found by laboratory tests that the addition
of Calcium Chloride in anounts up to 2 percent, added at the
batch either in solution or dry form, increases early
strengths without decreasing the effectiveness of the air

entraining material. Fig. 19.

VII. AETnODS OF fiEASUfiIEG AIR CONTENT IN PLASIIC

AND HAHDEJED COhCRnTE.
a. Determination of air in plastic.
b. Determination of hardened concrete.

nfiTHODS OF LEAJUZILG AIR COLTJLE IE EhnjiIC AJD

inJDEJJD CJJCRJTE
Gravimetric Lethod.

This is also called the unit weight method, and is
performed by comparing the wt. per cubic foot of the plastic
unxture (air entrained) with the theoretical air free unit
weight in secordance with A. S. T. L. hethod 0158-44. Je
have a precise knowledge of the Specific gravities, moisture
content of the ingredients used, and also the weight per
unit volume in order to arrive at accurate results.

Percent of air= Theoretical unit wt.-measured unit wt.
x 100

Theoretical unit wt.

a. s. T. M. Des. (0158-44) assumes that the difference
between the unit weight computed from the absolute volume
of the cement plus water plus aggregate and the unit weight
determined with the freshly mixed concrete is due to the
amount of entrained air in the mix.

Volumetric Method;

It is a method by which we can measure the amount of
air entrained directly and is described in a. S. T. M.
Method C173. The weight of the concrete per unit of volume
has to be determined and the displacement, in water of a
weighed sample of the concrete after elimination of the
entrained air from the sample while immersed in water. This
method is Open to errors in measurement and is also tedious

of execution. Errors may result from failure to remove all

the entrained air. In spite of these errors, it is still
considered to be a basically sound method.
Pressure Method.

The air content in concrete can also be measured by
the reduction in volume when an external known pressure
is applied to it. The amount of air can thus be easily
determined since this is the only compressible ingredient
in the concrete.

There is a Special magnesium alloy apparatus developed
to determine the air content of this method.

The concrete to be tested is placed in 3 layers in
the lower part in the same manner as is required for the
standard yield test (A. S. T. h. Des. 0138-44). The two
sections are joined and water introduced until the level is
above the zero mark in the glass gage, then adjusted by
bleeding to exactly the zero mark. An air pressure of 15
lbs. is applied by means of'a cycle pump. The‘water level
is read when the pressure becomes steady. This will be the
uncorrected value. Blank determinations on both sand
and coarse aggregate should be run correct for perosity of
aggregate grains. The sum of these two values must be sub-
tracted from the first reading to obtain correct gage glass

reading. The w of air in concrete: Vol. of air x 100.
Vol. of concrete

Camera Lucida Method for Determining Air Content of Hardened

 

Concrete.

 

This method involves the use of camera Lucida in con-

-45-

Junction with a suitable microscOpe.

A camera Lucida is a mirror (or prismatic) attachment
that permits the simultaneous viewing of both the Speciman
under the nicro-scope and an enlarged area on Which the
actual nicroscopic observation may be accurately traced.
In.this manner an enlarged tracing is obtained of the air
voids and aggregate particles in the suitable prepared
surface of the concrete Specimen. This method shows the
air voids the hardened concrete and also their size,
shape and distribution. There it can be used as a check
on the previous methods.

Method 0; Determining Entrained Air_in EreSh Uoncrete.

This method is used by State Highway Commission of
Indiana both in the laboratory and in the field and is
quite simple and accurate. It is based on the equation

Percentage of air= (T-AllOO in which T: unit weight
of the air free concrete, aid A3 unit weight of the concrete
containing air. The above equation is applicable regardless
of the method of employed for determining air content. The
determination of A.is made by the same procedure as that
employed in the yield test (cement content) using a 0.5 cu.
ft. cast aluminum yield bucket. T is determined by measur-
ing the volume, by displacement in water, of a sample of

fresh concrete of known weight. The apparatus used consists

of'the yield bucket and a nook gage which converts the device
into a pycometer the volume of which is calibrated wdth

-44-

water of known temperature (0.452 cu. ft. in Table 1). The
necessary data and computations for the complete air determin-
ation tests consists of four weighings, five subtractions,
three divisions, and one multiplication, all very simple to
do. Example is given in Column 1 of Table 1.

After A is determined the Operator removes concrete
from the yield bucket until approximately 30 lbs. remain
(line B, Table 1). fifter weighing (line D) sufficient
water is added to inundate the sample completely. The
hook gage is set in position and water added until the
"Dimple“ in the water surface breaks. The hook gage is
then removed and the gross weight obtained. From this line
D is subtracted to obtain line B, the weight of the water
to fill the pycnometer to the hook gage point. The weight
of the water is converted into cubic feet, recorded in line
G, and subtracted from the calibrated volume of the pycno-
meter (line V) to obtain line H, the absolute volume of the
concrete sample in cubic feet. T is then obtained by divid-
ing the weight of the sample (line B) by its absolute volume
(line H) obtaining as shown in the example 154.64 lbs. per
cu. ft. The formula (T-A)lOO is then used to compute per-

T
centage of air Which is recorded in line P.

Table l-- FQEM UsaD BY IHSPBCTQR IN THE FI

COMLISSION'OF IHDIAEA.

Alb; COii'i‘iniJ'l‘ 41.3031"

Contract No. Project No.

LD, STATE ;

Section

194

 

Test Humber l

Wt. of container and % cu.

 

 

 

 

 

 

 

 

ft. concrete 85,000
Wt. of container, empty,
clean and dry 10,000
Ht. 4 cu. ft. concrete 75,000
fit. of 1 cu. ft. concrete 150¢900 A
fit. of container and
concrete sample 40,000 D
Ht. of container, empty,
clean and dry 10,000
wt. of concrete sample 50,000 E
at. of container concrete
sample and water to gage
point 56.10
Wt. of container and con-
crete sample 40.00 D
Wt. of water to fill con-
_; tainer to gauge point 15.10 F
Vol. of water in cu. ft._§_
2.50 0.258 G
Calibrated vol. of container
at the hook gage point 0.452 V
Ices Vol. of water--cu. ft. 0.258 G
Absolute vol. of concrete sample
in cu. ft. 0.194 H
wt. of solid concrete on air free
b83113 L lb. 961‘ cu. ft.
H 154.64 T
nir content= T-a x 100
T 3.00 P

 

iodifiei lfiortar Voids liethod

_hodified mortar voids method is quite suitable for
design of concrete with air entrained in it. The relative
water content, an empirical factor used in the design, is
reduced from 1.215 to 1.15 to allow for the decrease in
water required for this type of mix. The yield and void
content are adjusted by reducing the sand content so that
the cement facuor is kept at 5.5 sacks per cu. yd. of
concrete and the total void content kept within specified
limits. These adjustments are made at the laboratory and
used in the proportional chart prepared for the Specific
materials to be used on a given project. The theoretic wt.
of the air free concrete is also given on the chart to
facilitate computations of air content in the field.

It is possible to adjust the amount of air entrained
to that reguired in both 0 see, when air entraining cement
is used or when the admisture is added at the mixer. In
case the air content can be raised by adding more of the
air entraining materials directly to the batch when air

entraining cement is used.

VIII. :dOPOhTIQiiIiiG 4.;niii0'DS

1.3:. 03 0:- ‘1' I 70;} Ira-G Lri 01) S

1. heed for Proper Control. The prOportioning methods
must be carefully taken into consideration in order to get
a uniform batch of concrete and so must be the handling and
weighing equipment. This will avoid variation in moisture
‘content and grading of the aggregates.

2. ImprOper placement, Spreading and handling in
forms may result in segregation, water gain, lamination,
and non-uniformity. Careful attention must also be given
to finishing and curing methods.

15. Preper consideration Should be given to the
location of the concrete structure with respect to water,
drainage facilities and general working conditions in order
to get a durable structure. Complicated forming and place-
ment of reinforcement steel should not be designed, because
in case of poor workmanship, it might result in inferior

finished product.

MIXING OPERATIOHS

Use of Automatic dispensing devices for the
admixture

Mix adjustment

Constructional practice

-50-

KIAING OPHHATIOES
Manufacture Of Air Entraining Concrete.

There are three types of manufacturing concrete, Site
maxed, central maxed and transit mixed concrete.

Site mix can be practised through a mObile concrete
paving mixer and stationary mixing plants at the site of
structures where the concrete is transported directly to
the forms by manually Operated buggies or by pumping methods.

Central mixed concrete is that which iS manufactured
at a stationary plant and transported over a considerable
distance by means of agitating or non-agitating truck
equipment.

Transit mixed is referred to concrete which is comp-
letely mixed in transit by Specially designed truck mixers.

a. The site nnx offers a very good control and
inspection of concrete manufacture. One minute is con-
sidered a good mixing time to obtain optimum air content,
while more time has to be given to smaller stationary mixers.

b. The air entrained concrete can.be mixed at a central
mixing plant and transported for a period of 90 minutes with-
out any effect on either the air content or the slump. Dump
trucks and truck agitators have been successfully used to
transport the mixed concrete to the point Of delivery. The
mixed-concrete can also be tranSported in truck mixers,
Operating at agitator Speed. The good Spped for truck

agitation is 2 rpm.

-51.-

0. Transit mix procedure is not recommended for air
entraining concrete as no definite control can be exercised.
The following are the main objections to it:

1. Due to change in consistency with distance,
time of haul and time of discharge the amount of water
used has to be in excess of that in the given.design
to compensate for drOp in consistency.

2. The air content will also vary.

5. Two trucks would be required for handling con-
crete and both won't give uniform results.

4. Complications arise due to delay in traffic.

5. Greater difficulty in Smooth running.

Automatic DiSpensing Equipment for 4i; Entraining materials

Most cement mills use automatic diSpensing equipment
in the manufacture Of air entrained cements nowadays.

A metering device is necessary when air entraining
materials are added at the mixer in order to get accurate
results. Such dispensing equipment can be bought in the
market.

Agjusting the Mix to Meet the Desired Air Content.

If a trial batch shows that the air content is not
within a permitted range, say 3-6%, it may be possible to
adjust it by changing the sand content, taking at the same
time into consideration avoiding an over sanded or under
sanded mixture. If the difference is not tOO great it can
be removed by drying or adding a little water. The air con-
tent may also be increased by increasing the mixing time,

-52.-

which is very effective wnen the cement hrs been ground with
powdered or flake Vinsol resin. Blending in plain Portland
cement may correct excessive air due to long continued mix-
ing.
Constructional Practice

Air entrained concrete is more sticky due to its
greater plasticity and cohesiveness as compared to plain
concrete, with the result that it sticks to the screed of
road finishing machines and thus tears the surface. This
is more true in case Of richer mixes. This can be corrected
by increasing the number of transversal Oscillations of the
screed per foot of forward motion. steel tools have been
used for final finishing in some cases. There is little
or no bleeding (water gain) between the initial screeding

and final hand finishing, it is necessary to keep all finish-

')

ing Operations vell up behind the mixer, particularly in

hot dry or windy weather.

1

‘Tm' ‘ L‘" ,- "2"" . f H." '.""
A JUL/AL. M‘IJH‘.‘ $411.4. .5. 4.5.40

a. Darex AHA “
b. btewart Field uemonstrates Value of Air
Lntrainment (Extract)

.‘._ -"'.-.w-

0" 5;; '1‘2“.‘ r " rein" ,1 BY ~ -. , “‘3‘! 7? ...- ’rr'\ 7
1; -‘ >-' ' »-' ' r ~ ‘ ' 4
u‘h-L‘Q‘VL J‘hufidé “~\ f.-.‘ U-LJJJ 4,-urJ d-.o . 1. it... Lu....r.d-JU i
p 'T if: ’m'rr -.“.
r;-..L) --'1Liv;i_..a.

Darex ALA.

 

This is an air entraining agent manufactured, developed
and produced by Dewy and Almy Chemical Co. and is now being
used in the manufacture of air entrzining cement an» as an
addition at the mixer on field construction jobs, at ready
mixed cencrete plant” and in concrete product plants. This
material was originally intended as a companion product to
iDA; that is as an air entraining agent and grinding aid
for Portland cement.

Principle of gauge water addition is most favorable
and easy'hethod of controlling the air content. Measure-
ment of the entrained air is by making unit wt. determin-
ation on the grren concrete and so the amount of entrained
air can be adjusted as to the required need.

Air content afiects richness of mix, water content or
slump, graduation and percent of sand.

Dares AHA is delivered in a neutral solution ready
to use.

Batching methods have been deveIOped to dispense
accurately any predetermined quantity of this solution;
Quantity rigid in each batch is small, in most concrete it
amounts to from one to one and one half fuild Ounces per
sack of cement. -

With 5p air entrainment using Darex AHA either as an

-55-

interground ingredient of the cement or as a gauge water
addition, there is not the loss in strength generally
associated with air entraining concrete.

Table 1 gives results of field tests made on ready
mixed concrete. This shows the reduction in water content
with the use of Darex AEA with no change in slump. The
reduction in water tOgether with the Darex ABA acts to
increase the strength of the cement paste so as to offset
the strength loss which naturally results from the inclusion
of air in the concrete. The table also shows the gain in
strength which may be expected for mixes leaner than five

sacks of cement per cubic yard and that for the richer

mixes, the strength loss is relatively small.

 

EFFECT OF DAREX ABA ON COSCRETE COMPRESSIVE STRENGTHS
(Typical Data)

 

 

Sacks 575 Slump Weight Compressive strength
Addition cement by inches cu. ft. 7 days 28 days
cu. yd. Wt.
None 3.90 .753 1.25 150.0 1500 3130
Darex AEA 4.05 .610 2.00 144.6 2766 3930
None 4.40 .710 3.50 152.1 1580 2400
.DarexyAEA 4.60 .636 3.00 146.6 2480 3540
None 4.93 .602 2.00 150.0 2640 4495
Darex AEA 5.06 .522 2.13 145.0 3130 4450
None 5.53 .575 3.00 152.1 3075 4850
Darex ABA 5.53 .510 3.00 146.0 3100 4930
None 5.79 .550 2.00 153.0 3120 4600
Darex LEA 5.87 .483 2.00 174.0 3365 4670
None 6.00 .530 3.75 147.5 2940 4730
Darex ABA 6.00 .490 3.25 143.6 3225 4875
None 6.60 .496 5.00 152.9 3600 5300
Darex AEA 6.50 .467 4.50 147.7 3650 5270

 

Production of concrete pipe by the temp method it is
desirable to have a small amount of plasticity in order to

-56-

get better compaction and also improve its appearance and
lower absorption. The improvement in compaction diminishes
the danger of collapse of the green pipe during the stripping
Operation. Too great plasticity is also undesirable as the
mix becomes mushy and tamping sticks are broken, thus hinder-
ing production. The amount of air entraining agent required
is about one half the amount used normally and it is desir-
able to change the quantity accordingly to changes in aggre-
gate grading. In the Packerhead process, the amount of air
entraining material used is approximately twice as much as
would be used normally. :he use of Darex AEA could give
sharper corners and edges on the pipe. It also reduces the
sucking action which is of great help in stripping Operations.
The pasticising action of the air entrainment agent enables
the concrete to flow more readily around the reinforcing

wire so that dislocation of the wire is minimized.

The use of Darex AKA in building block results in
improved surface texture reduced absorption, increased
strength and elimination of green breakage and culls, that
ordinarily are the result of adverse changes in aggregate
graduation. Larger quantities of the entraining agents
are used than ordinary, and the optimum quantity determined
by actual performance.

The advantages of using Darex Ads in the manufacture
of case stone are:

1. Greater plasticity resulting in better filling of

the mold.

2. Reduction in bleeding and segregation.

5. Greater durability of the finished product.

‘TEflAfiT FIELD DfimOhSTRATfiS VALUE OF AIR ELCRLIKRENT.
TAn Extract)

Stewart field is the U. S. Military Academy’s airfield
at Westpdint has shown the benefits of air entraining con-
crete as used by Corps of Engineers for all the complete
job. Eighty-two percent of all paving which equals 1.29
million square yards of concrete and three auxiliary air-
ports contain over 500 thousand sq. yards of paving of
which 62 percent is concrete. Air entraining agents were
used in all these four aerodromes except for a small portion
of Stewart Field.

A typical cubic yard mix consisted of 6-1 sacks of air
entraining cement; 1142.9 lbs. of sand; and equal amounts
of two sizes of gravel (1% inch and 5/4 in.) or 1003.5 1b.
With 5 gallons of water per sack of cement, this mixture
yielded an airless volume of 25.98 cu. ft. The theoretical
wt. of the concrete at this yield was computed to be 153
lbs. per cubic foot. the actual measured wt. per cubic
foot was 146.9 lb. making actual yield 27 cu. ft. With
these aggregates, the amount of air was found to be 4 per
cent by neight.

The aggregates used, local sand and gravel, Long Island
sand and crushed stone; and manufactured dolmitic sand and

local gravel. Air entraining cement used met the Federal

Specification that the cement be treated with Vinsol resin,
in an amount not less than 0.025 percent and not more than

0.045 percent by wt. of cement.

 

 

Average Compressive Dtrengths °
1944 works 7 days 5182 psi 559 psi
1944 torks 28 days 4611 psi 700 psi
1944 works 90 days 4769 psi 741 psi

 

° Average flexurel strengths.

ihree 6x12" cylinders and three 6x6x28" beams were
made for each day's run.

Adv. fair entrainment:

1. Better workability with stone, sand used.

2. Practically no bleeding

5. Only normal finishing Operations were required.
Design Metails

Pavement design for a 8-6-6-8 cross section for each

25 ft. strip the thickened edge being attained in a distance
of 3 feet irom the longitudinal tongue and groove construction
joints. xt longitudinal eXpansion joints and at outside
runway edges, the edge thickness was attained in a one lane
thickness or 12; ft.

_Transverse eXpansion joints are spaced every 100 ft.,
with intermediate eXpansion joints of the dummy type sapced
on 20 ft. centers being out one quarter of the pavement
depth except on 1944 work where they were cut to a depth
of one third of the slab thickness. L11 eXpansion joints
have 3/4 inch non-extending filler. iransverse expansion

-Rg-

Lv‘

joints have as load transfer units 1 inch palin round bars,
24 inch long Spaced 12 inches on centers. Half inch deformed
tie bars 30 inches long set 30 inches apart were used in the
joints longitudinal dummy joints adjacent to longitudinal
expansion jts. and the outside edges of the runways.

Eremolded bituminous fiber ribbon 1/8 inch x 1% inch,
was used in longitudinal dummy joints in 1945 construction.
fhis practice was drOpped due to light spelling along this
type of joints. Spelling Occurred when the tOp of the
ribbon was below the surface of the concrete and not when
it was above or levelled with it.
heinforcement

NO reinforcement was used in any slab except for small
apron areas amounting to less than 1p.
Subsoil

Gravel blanket with a minimum depth of 12 inches was
laid and compacted due to poor supporting quality of the
subsoil. Bearing tests on this prepared subgrade using a
30 inch diameter plate showed an average bearing strength

Of 55 psi. at a 0.1 inch deflection.

. Construction Equipment

Batches averaged 56 cu. ft. and transported from central
plant to pavers in two and three batch capacity trucks.
Mixing water was supplied by tank trucks. The batching
plant was equipped with a 585 bbl. bulk cement bin and weigh-
ing hOpper (screw conveyor and bucket elevator) and a 150,
ton three compartment ags. bin with weighing hOpper.

-60-

 

Production

For 343 average daily production was 600 cu. yd., max.
846 cu. yd. Ehis equivalent of 1200 lineal ft. and 1700
lineal feet resp. of 25 ft. wide slab. Concrete was

vibrated along the sideforms and the joints.

Use of Color Pigments on A;£:§ntrainment.

Color pigments made from iron oxides can be used
successfully with air-entraining without any loss in
strength, durability or scale characteristics of the con-
crete. experiments run by the Kational Urushed stone
Association show that air entrainment in concrete contain-
ing limestone aggregates both coarse and fine, materially
improve durability and resistance to scaling. Fig. 20.

It also improves excessive bleeding, poor workability and

difficult finishing.

Application of Air Entrained Concrete.

Air entrained concrete has been used to great advantage
in general concrete work such as foundations, walls, paving,
sidewalks, slipform work, granite, and in concrete pipe and
block.

Main eXperience in the use of air entrained concrete
has been in the field of pavements, however excellent resis-
tance to alternate freezing and thawing indicates that it

should prove advantageous in the construction of bridges.

user RhOCnnonE FOLLQtED BY CCADON

The following describes the test procedure adOpted by
Cordon for all the results shown in Fig. . In the 102
concrete mixes a range of slumps, water cement ratios, air
percentages, brands of cements and types of aggregates were
included. The percent of entrained air used was found by
absolute volume method and was an independent variable through-
out the entire investigation, and the amount of air in each
set of 6 mixes was varied by increments of 1 percent from
approx. 0 to 6 percent. Agent was added to all mixes to
obtain a pre-established percentage of air regardless of
the amount of agent required. A standard solution of
Vinsol Eggig was made before the mixing pregram started,
and this supply was used throughout, with the exception of
12 mixes in which another commercail air entraining agent
was used.
Mixingpfrocedure

All the mixing was done in a 1% cu. ft. tilting labor-
atory mixer with a mixing period of 5 minutes. The follow-
ing was the charging sequence:

1. One half of the mixing water and agent,

2. sand, gravel and cement combined,

5, remaining half of mixing water and agent.

The air entraining agent was combined with the mixing
water before introduction into the mixer. After the mixing

period, the mixer was discharged into a large pan and re-

worked with a shovel. The following tests were made on
each batch of fresh concrete:
Slump test -- ASTM Des. (0145-59)
Unit weight -- Adim Des. (158-44)
:gpwers hemolding Testifor Workability"
- Three 6x12 inch cylinders from each batch were tested
for compressive strength, AJTM Des. (C192-44T), and elastic
properties.
Modification and Adjustment of standard Computations
Table 5 of the 301 Standard Recommended practice for
the design of concrete mixes can be slightly modified for
air entrained concrete by including the following information:
a. deduce the sand percentage by one for each percent
of air entrained.
b. For air entrained concrete, reduce the water content
8.5 lb. for well rounded natural aggregate and 10.5
lb. for angular aggregate for each percent of air
entrained.
c. For the same N/C ratio reduce strengths shown in
table by 200 psi. for each percent of air entrained
in concrete.
Computation of Trial Mixes.
Me can very easily modify the trial mix computations
as outlines in the recommended practice and allow for entrained
air by simply treating the air as another ingredient of the
concrete mix which replaces an equal volume of aggregate.
The sample computations shown on pages 657 and 658 of the

-63—

above mentioned standards can be modified as follows:

(Assuming 3p air)
Cement content net water content _ 505 . 575 lb. per
water cement ratio 0.55

cu. yd.. 575. 6.12 sacks per cu.
94
absolute volume water 9 cement

“d.

C.

 

Jatcr content *

cement content 505 __ 5 7.81 cu. ft.
spec. ;TaVlt; x 63.4 6L.é 5 15x63

£l_'r 011. Lido C);Urete
absolute vol. air- percent air x cu. ft. per cu. yd.
of concrete
absolute vol. of total a gregate 27 - abs. vol.
(water cement) - ab . volume of air 2 - 7.81-
0.81‘ 18.58 cu. ft. per cu. yd. of concrete.

(ii

I“

C

J

Absolute volume 0 sand percent sand x absolute vol.
total aggregate: 0.42 x 16.50* 7.72 cu. ft. per
cu. yd. of concrete.

Absolute volume of coarse aggregate» abs. vol. total
aggregate - absolute volume sand3'18.58 - 7.72~
10.66 cu. ft. per cu. yd. of concrete

sand content: absolute volume x sp. gravity x 62.4-
7.72 x 2.55 x 62.4:.1,277 lb. per cu. yd. of
concrete

Coar

(D
m

s ggregate content 10.66 x 2.55 x 5
per cu. yd. of concrete

lo

0

,p.
H
G;
(.0
O:
H
0‘
0

Trial an proportions 575 : 1,277 : 1,696 g 1: 2.22:
575 575 575
2.95 say 1: 8.2: 5.0

Computation of air Content

For mortar containing soap forming materials earn Des.

(01750429 "Test for air content of concrete" is not re-

commended. The best method is nan-.1 Des. (0158-44) which

assumes that the difference between the unit wt. computed

-54-

 

from the absolute volume of the cement plus water plus
aggregate and the unit weight determined with the freshly
mixed concrete is due to the amount of entrained air in '
the mix.

The percentage of air (Theoretical unit wt. - measured

unit wt. x 100
theoretical unit wt.

Using weights computed in the foregoing trial mix comp-
utation, the percent air can easily be determined as follows:

(Measured unit wt. 142.7 lb/cu. ft. )

wt.
Theoretical unit weight weight cement + weight wateri egg.
solid volume of cement + wa er +

cement

575 + 305 172975 ., 3855 1 147.1 lb.
27 "‘ 0081 > 2619 cu. ft.

and W air 147.1*;,142.7 x 100; 5.0 per cent
147.1

Designation 24 of the U. S. Bureau of Reclamation concrete
manual outlines a general method for the computation of per
cent voids based on the actual mix parts of any combination

of cements, water and aggregate. Sollowing is simplified

form of the method described:
-1— ' W/C ‘ is 100w

 

Percent air, 100 - Ge GA where
P xTotal parts (cement, aggregate, water) in mix (by
weight).

BA= Parts of aggregate (by weight).

G0: Specific gravity of cement

GA: Specific gravity of aggregate

W : Measured unit wt. of fresh concrete

W/Q-*Water cement ratio lb. per cu. ft. by weight.

-65-

l.

10.

ll.

BIBLIOGRAPHY

Entrained Air in Concrete Inst.--V17N6, June 1946,
Symposium includes papers by W. A. Cordon, L. E.
Andrews, 0. Walker & D. L. Bloem, H. L. Kennedy,

W. H. Klein & S. Walker, S. W. Benham, E. W. Scripture.

Air Entraining Cement for D‘tructural Concrete-~Am.
Bldr. & Bldg. V 69R, February 1947.

Air in Ready Mixed Concrete--E. L. Howard & G. W. Greene
Concrete, V55N, 1947.

Camera Lucida Method for Measuring Air Voids in Hard-
ened Concrete-~G. J. Verbeck, Am. Concrete Inst., J. V.
18N9, 1947.

Measurement of Air Contents of Concrete by Pressure
Method-~H. W. nussel, Am. Soc. Testing Letals, reprint
in S. S. June 16, 1947.

Addition of Air Entraining Agent at Concrete Mixer ~
Advocated--C. L. Wuerpel, Civil Eng. V16N, 11-1946.

Air Entrained Concrete--D. H. L. Keekle, Surveyor, V.
105N2862, Nov. 29, 1946.

Application of Air Entraining Agents in Concrete and
Concrete Products-~H. M. Kennedy and E. M. Brickert,
Pit & Quarry, V. 58, March 1946.

Laboratory Studies of Concrete Containing Air Entraining
Admixtures--C. E. Wuerpel, Am. Concrete Inst.--JV17N4,
Feb. 1946.

Stewart Field Demonstrates Value of Air Entrainment--
Concrete V54, Oct. 1946.

Effect of Air Entrained on Durability of Concrete Pave-
ment in Ohio. J. F. Barbee, Crushed Stone J., V22N-1,
march, 1946.

Entrained Air--Its Effects on Constituents of Portland
Cement Concrete.

Field Use of Cement Containing Vinsol Resin--C. E. Wuerpel
Am. Concrete Inst., JVl7fil, Sept. 1945.

Some Effects of Air Entrainment & Coarse Aggregate Type

on PrOperties of Concrete--C. E. Huerpel, Crushed Stone
J., V205 2, June 1945.

-65-

15.

16.

17.

18.

Studies of Concrete with Entrained Air-~D. L. Bloem &
S. L. balher, Concrete V55 N B, Aug. 1945.

Use of Ready Mixed Concrete in Highway Construction--
J. F. Barbee presented at 10th Resting of National
Ready Mixed Concrete Assoc., Jan. 20, 1948.

A Working Hypothesis for Further Studies of Frost
Resistance of Concrete--F. C. Powers, A. C. I. Journal,
February 1945, Vol. 16, No. 4.

Air Entrainment in Portland Cement Concrete-~A. A.
Anderson-~Ohio State University Exp. Station Bulletin
No. 129, Vol. 16, K0. 5, Sept. 1947.

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