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THE EFFEBY 0F CURING CQNBHWNS @N THE TENSILE

STRENGTH 0F SUPER GEM?” MRHRS

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THESIS

The Effect of Curing Conditions on the Ton-113

strength cf Super Cement Mortars.

A Thesis

Submiitod to the Faculty of

The

LICKIGAN STLIJ CULLSGE

of

Agricultura and Applied Science.

by

3.0.Avory.

Candidata for the Degree of

Baoholor of Science

June, 1926.

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.

Peerle s Super Cement is made by the Peerless Portland(D

Cement Co. at Uxion City, Mich.It is a discovery of an Eng-

lishinvestigator and was successfully used in Great Britian

a number of years before its introduction into Canada in 1920.

Super Cement is merely a more efficient form of Port-

land Cement and is rendered so by the incorporation of a

substance known as “Catacoll” during the manufacturing Pro-

cess. Catacoll itself has no more cementing value than raw

gypsum ordinarily used in the manufacture of Portland Gem-—

ent, a portion of which Catacoll replaces.It occupies no

greater volume and is anything but a water repellant.The

strength and impermeability developed in Super Cement mcr-

tars are derived from the reactions which occur between the

m1Xing water and the constituents of the clinker. fhe fun—

ction which Catacoll accomplishes is to facilitate these

reactions and thus insure that they will be more complete

than in the case of Portland Cement.

Super Cement hydrates more thoroughly than Portland.

Cement depends upon this prOperty far its strength and den-

sity. Consequently, greater strength in bond, tension and

compression can be expected from Super Cement mortars.

Super Cement is more efficient as a lubricant to the

mix thus minimizing the tendency toward segregatin— in and-

ling. As a result of this greater efficiency, Super Cement

produces a concrete of sufficient density which is so im-

pervious that no other means of water proofing is necessary.

Exactly the same machinery is used to powder Super

Cement as is used for Portland, but the Super Cement seems

93813

to be more finely ground. It has no initial set but produces

a uniform set curve from cast to final set. The forgoing was

taken from a bulletin published by the Peerless Cement Co.

In testing for the effects on the tensile strength of

mortar produced by different methods Of curing, a 1:3 mix of

normal consistiency was used. The normal consistiency of neat

cement was 253 and of a 1:3 mix, 15% of water by weight. The

sand used was cleant sharp and dry,and passed a no. 20 sieve.

The specimens were of the standard size adOpted by the Amer-

ican Society of Testing Materials and were tested at the end

of I,2,3,5,7,I4, and 23 days. Four briquettes were used for

eacn test and the average strength of the four taaen as the

final result. If a.specimen showed signs of weakness, i.e.

POOTIY tamped etc. and the strength fell much below theaver-

age of the others, it was discarded.

Different methods of curing were obtained by varying the

time that the specimens were left in dry air, moist air,and

water and also by changinv the briquettes from one medium to

another at different ages of the curing. The standard method

adOpted by the A.S.T.M. is to place the specimens in moist air

'for the first 24 hours and the balance of the time in water.

This method was varied by curing the first day in moist air

and then changing to dry air the 2nd, 3rd, 4th and 5th, 6th

and 7th, 2nd week and tne last two weeks, testing the Spec-

imens at the above mentioned intervals. Also specimens were

cured by placing in moist airxlry air, and water for“ the fU1l

28 days. modifications were also made from these by changing

to other mediums at different ages of the curing.

The results obtained from the series of tests seem to be

rather mystifying. It is a recognized fact that to elpose

Portland cement concrete to dry air isdetrimental to the final

strength of the concrete. This does not seem true for Super

Cement mortars, unless the exposure to dry air is very pro-

longed. Exposure to dry air not only hastens the set of the

mortar but actually seems to increase the final strength at

the end of the 28 day period. It was found that the mortars

could be exposed to dry air for the first 5 days and the rest

of the time in water and no harm done. In fact, the strength

at the end of 28 days was greater than that obtained by our-

ing the standard way. The highest strength, tho, was obtained

by curing the standard way for the first two weeks and then

exposing to dry air the last two weeks. Curing the full 28

days in dry air gave practically no strength at all. the mortar

almost crumbling at the touch.

cured

The final strength of thosefithe full 28 days in water

was almost as much as those cured the standard way,but the set

for the first few days was greatly retarded. Also, great care

had to be exercised when placing the specimens in water or

much of the mortar would wash away.

The conclusions arrived at thru the series of tests ind-

icate that to get the strongest concrete, cure the standard

way,i.e. keep the concrete as wet as possible for the first two

weeks and then expose to dry air after that.Also great care

must be exercised when placing Super Cement concrete under

water or much of the fine mortar will wash out and the strength

of the concrete will be greatly reduced.

The following is a table of the actual strengths as tested.

The letters under the ages at which the specimens were tested

denote how the Specimen was cured from the precceding testing

day to the one at which the test was made.For example,D under

the second day means that the Specinen was cured in dry air for

the second day, or D under the 3rd day means that the Specimen

was cured in dry air the third day or from the 2nd testing

period to the 3rd testing period etc.

Legend: 3- dry air.

M- moist air.

3- water.

The numbers under the letters give the average strengths

in pounds per square inch as tested.

Table of tested strengths.

Age of specimen (days)

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- 60 90 I40 210 240 260

In D ‘I W .) VJ J d J

- 60 I45 185 200 220 260

h N D J 'J W J

- 6O IBC I85 200 250 295

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A 55 95 225 230 250 290

K W W W D ’H ‘H

- 60 85 I50 220 255 275

IS ?7 if if 3? I) ll

- 60 90 I45 20 245 500

It: I"; W Y; W w D

- 65 IOO I50 215 250 400

D D D D D D D

50 100 12 I30 150 IIO 80

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Age of specimens (days)

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