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FFECT OF CALCIUM CHLORIDE

e:

ON

PLAIN AK REINFORCED CONCRETE.

A Report Submitted to the Faculty
of
MICHIGAN AGRICULTURAL COLLEGE

By

Roscoe J. §}ack H. Firth Anderson

Candidates for the Degree
of
BACHELOR OF SCIENCE.

June, 1924.

THESIS

1 .l
L; m’. 7‘ 1 A.

INDEX.

Effect of Calcium Chloride on Plain and

Reinforced Concrete ....................

Specifications ............................... a---

External Treatment -------------------------------

Internal Treatment ...............................

Percent of Calcium Chloride ......................

Effect on Steel ..................................

Bond Strength ....................................

Conclusions ......................................

940?3

17

13

. _.....
......_..

_-.—._—.

EFFECT OF CALCIUM CHLORIDE
0N
PLAIN AND REINFORCED COECRETE.

There has been a problem of rapid and economic
curing without any injurious effect on the concrete or
the reinforcing since the time that Portland Cement has
been used with various aggregates to produce concrete.
Up to the present date various salts and chemical
compounds, which weaken the concrete, attack the steel,
or stain the surface, have been tried. While the
laboratories were working on this prdblem, the most
efficient methods of curing concrete were: first,
ponding or covering with moist earth for pavements, and
second, keeping the forms moist for structures. These
methods are very uneconomical for the present day system

of building pavements and structures.

With a quick set, roads may be opened to traffic

and forms for structural work may be removed at an earlier

date than is possible, otherwise. The Opening of roads
at an earlier date will greatly reduce the expense to

the traveling public and also the expense to the community

in the upkeep of detours. It will reduce the contractor's

expense; so that, ultimately, the concrete can be laid
more economically than by former methods.
In structural work the owner's expenses will

be lowered if the contractor is able to remove the forms

and complete the structure more quickly. In cold
weather, the time and cost of protecting the concrete
from freezing will be materially reduced.

A few years ago, calcium chloride was placed
upon the market to accomplish these purposes. Very few
tests of this salt, used for curing concrete, are now
available. At the present time, the Portland Cement
Association, the Illinois Division of Highways, and the
U. S. Department of Agriculture are the main investigators.

The chemical action of calcium chloride in
curing concrete is not known. The theory is that it
depends upon the hygroscOpic properties of the calcium
chloride and its ability to absorb moisture.

Tests were made for bond, compression, tension,
time of set, hardness and surface condition of the
concrete when treated externally with calcium chloride.

Four specimens were used for each test.

SPECIFICATIONS.

The volumetric mix of 1:2:4 was used for all
specimens except briquettes. Huron cement was used in
all cases and the aggregate used was washed pebble and
sand. The volumetric mix for the briquettes was 1:5,
using Ottawa sand, except in the case of neat cement
specimens.

For internal treatment, the calcium chloride
was dissolved in the mixing water in various percentages
according to the weight of the cement. The external
treatment was by placing calcium chloride on the surface
in lbs. per sq. yd. of surface treated. The calcium
chloride was that commercially known as Dow Flake.

All coarse aggregate specimens were allowed to
cure in the open without any covering or attention. The
briquettes were cured in a moist chamber for 24 hours and
then part were cured in water and the remainder were cured
in air. All specimens that did not contain calcium
chloride were cured in water.

SPECIMENS.

    

--------

EXTERNAL TREATMENT.

When the surface is treated with Ca012
for the purpose of curing the concrete, the effect is
noticable for a depth of i to 5/4 of an inch. The
concrete for this depth remains soft and spongy for some
time but finally sets up forming a scale on the surface
which wears off very rapidly. The penetration depth is

shown in Fig. 2, for a neat cement briquette.

SHOWING THE DEPTH OF PENETRATION 0N NEAT CEMENT.

 

If the air is dry and wanm the surface layer
sets in a few days but if cold and moist it takes much
longer. The surface hardness is affected by the chemical
whereas the hardness of plain untreated neat cement is
5 3/4, treated with 2 lbs. per sq. yd. is 2 1/2, treated
with 5 lbs. per sq. yd. is 2.

The surface treatment discolors the surface,
giving it a mottled effect. When the chemical is not
evenly distributed it will pit the surface where the
chemical lays in lumps, giving it the appearance of
having been rained upon before it had its initial set.

Dow Flake has a deleterious effect upon the
surface layer but the main body of the concrete is equally
good to concrete cured by the pending and moisture earth

methods.

SHOWING THE RIEHLE TESTING MACHINE.

 

SHOWING THE MOT’ELING EFFECT AND FITS.

 

INTERNAL TREA THEN T.

Tension tests were made upon specimens
containing different percentages of calcium chloride
dissolved in the mixing water. The specimens that were
cured in air showed a greater tensile strength than those
cured in water. By observing the curves plotted on the
following pages representing the two curve Specimens having
the same amount of calcium chloride in the run.nearly
parallel after they reach the peak.

The chemical action, as far as we have
investigated, cannot be determined, but we do know that
calcium carbonate was the result of the chanical action.
This may have been an action with the water as the mixing
water contained carbonate from the chemical analysis. The
calcium carbonate formed came to the lower portion of the
briquette and formed stalactites, as shown in the Fig. 4,

The chemical had the same effect on neat cement
briquettes as it had on the briquettes of the 1:5 mix.

It was more noticeable in the neat cement Specimens, as
there was a greater difference in the tensile strength at
the end of twenty eight days, than in the test made on the
former.

Although concrete is very seldom called upon to
take any tension, there might be a time when the tensile

strength would be necessary. However, from the above

facts we draw our conclusion that when calcium.chloride

was used internally there must have been some injurious
chemical action to reduce the tensile strength, cured
in water.

The time of set is shown by the graphs. The

greater the percentage of calcium chloride the greater

the set.

CURED IN AIR.
PERCENT OF CALCIUM CHLORIDE.

 

 

Days 0 .2 5 4 5 5
2 241 242 257 282 208
4 280 282 285 510 255
7 285 285 285 304 225

14 290 285 279 271 202

21 297 280 249 241 198

28 298 . 280 245 238 198

CURED IN WATER.

2 62 190 190 180 155 120
4 124 255 245 350 173 155
7 227 271 255 240 187 161
14 552 274 265 247 195 165
21 590 277 266 250 195 165

28 450 280 268 250 195 165

10

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after inspecting the results of the compression
tests made by the Illinois Division of Highways, we
hesitate to advance any theory, as to the results of the
compressive tests. Their tests were made using twelve
different brands of cement, all of which passed the
state Specifications for both physical and chemical
tests.

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Specimens containing calcium chloride increases up to
and including 5%, after which the compressive strength
decreased. All compression tests were embedded in plaster
paris which were allowed to set before putting any stress
upon the specimens.

COMPRESSIVE STRENGTH IN LBS. PER SQ. IN.

 

Ca012
percent 7 days 14 days 21 days 28 days;
0 1170 1800 2265 2500
2 1450 1855 2375 2625
5 1870 1925 2220 2715
4 1960 2100 2155 2160
5 1760 1900 2020 2260
B 1685 1895 1955 2190

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EFFECT ON STEE.

The bond strength of concrete containing 6%
calcium.shloride was greater than that which was not
treated internally. The only way we can account for
this is that the chemical attacked the smooth surface
and gave the concrete a chance to cling to the surface.
The bond strength was a great deal higher than that
allowed in H001 and Johnson's Handbook, but this is
accounted for by the factor of safety. But we could
not say whether the bond would be affected by time, as
the bars were rusted, which will be discussed in the
next paragraph.

The effect of calcium chloride in the concrete
tended to rust and pit the steel. All steel embedded in
the specimens was inspected carefully before it was
.placed in the concrete. The steel used was smooth cold
rolled with a low carbon content. Steel placed in
concrete that was not treated with the chemical, was not
affected, even though it remained in water for 28 days.
When steel was placed in water for 10 days, it showed
corrosion, but not as fast as when it:was placed in
concrete that was treated with the chemical. A Specimen

showing the corrosion of the steel is shown.

13

BOND STRENGTH.
BOID II LBS-PER 3Q. II. AT 88 DAYS.

Per cent of Ga 012

 

130

8 3 d 5 6
815 847 270 293 882

SHOWING RIEHLE COMERESSIOI IACHINE

 

 

FIGURE

SHOW HG CORROSION OF STEEL.

 

14

15

NORMAL COKSISTENCY.

Standard tests for normal consistency by the use
of a Vicat needle were performed. The amount of water
expressed as a percentage of the dry cement to obtain the
normal consistency was reduced by the addition of calcium

chloride. These results were as follows for neat cement.

% of 03012 0% 1% 2% 3% 4% 5% 5%

% of water 26 26 25 25 24 24 23

Standard Gillmore needles were used in making the
tests for the time of set. The cement was mixed to normal
consistency.

These tests were made when various percentages
of calcium chloride were used. A cement may set so
quickly that it will be worthless for some kinds of work;
since handling cement after it commences to set weakens
it and causes it to disintegrate.

From the data and the graphs which follow it is
seen that calcium chloride greatly accelerates the set.

TIME OF SET.

D 1 3 3 4 5 5
6/; Of C8012 be me be me he me he 111. he 111. he me he 111.
Initial Set 2 5 1 35 1 15 O 24 0 9 O 2 0 1

Final Set 6 50 3 46 2 33 l 48 l 2 O 28 O 10

Ho 02*:

Time offer

by
G /'//mare Need/(.5

 

 

 

0 2. ’1‘ 6

Per: epf Ca Cl,L

CONCLUSION.

The results secured in these investigations,
to hasten the set, satisfy us that calcium chloride could
be incorporated in concrete to advantage under certain
conditions, such as concrete which will be used for
pavements, and slabs that do not contain reinforcing steel.

The surface treatment for curing can be used in
place of the ordinary methods of pending or using damp
earth for covering,but care should be taken in Spreading
the chemical over the surface so as to insure an even
coat to prevent unnecessary pitting.

We found that by treating internally the bond
strength was increased in preportion to the amount of
calcium chloride used,but in turn, the effect upon the
steel is very deleterious as rusting takes place
immediately.

Also,that calcium chloride when used internally
in concrete which is allowed to set in water does not
get the desired strength.

In conclusion we recommend using calcium

chloride as an agent, for curing and hastening the net

that it be limited to 3% of the weight of the cement
for internal treatment,and 21bs. per sq. yd. for

surface treatment.

BIBLIOGRIPHY.

Report of tests conducted in an investigation

to determine the effect of calcium

chloride in concrete on compressive

strength. U.S. Department of

Agriculture ------------------------- J. H. Bateman
Cutting down curing period for concrete

roads. Illinois Division of

Highways, 1924 ---------------------- H. F. Clemmer,
An Investigation of the use of calcium

chloride as a curing agent and

accelerator of concrete. Illinois

Division of Highways, 1925 ------- --- H. E. Clemmer,
How to cure Concrete -------------------------- Dow Chemical
Company,
How to maintain Roads ------------------------- Dow Chemical
Chm‘pany.

Discussion of the paper presented by mr.
Clemmer on "The use of calcium
chloride as an accelerator in

concrete hardening." U.S. Bureau

of Public Roads. -------------------- H. F. Clemmer,
Concrete Engineers' Handbook, 1922, ----------- Hool & Johnson,
Protection of cold weather concrete ----------- Portland

Cement Assoc.

Economic Value of Mixtures, American

J. C. Pearson,
Concrete Institute ----------------- -

F. A. Hitchcock,

Winter-built Concrete ------------------------- Portland
Cement Assoc.

 

 

 

 

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