TECHNICAL INFORMATION ON BUILDING MATERIALS

ECR USE IN THE DESIGN OE LOW-COST HOUSING

THE NATIONAL BUREAU OE STANDARDS

UNITED STATES DEPARTMENT OE COMMERCE

WASHINGTON, D. C.

TIBM-S

Anril 30, 1930

CALCIUM CHLORIDE AS IT AEEECTS PORTLAND CEMENT AND CONCRETE

This is a Brief digest of Research Paper R.P. 7^2, "Effects of

Calcium Chloride on Portland Cements and Concretes" , (April 1935)

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By Paul Rapp, issued By the National Bureau of Standards, covering a study to determine the effect of the addition of calcium chloride to

Portland cement mortars and concretes on the setting times, heats of

hydration, consistencies, and the strengths at various ages under

several curing temperatures.

Materials used: Eight commercial portland cements (hereafter re- ferred to as standard cements) , one high-early- strength and two white

Portland cements were used, which were of widely varied composition

and physical properties.

' The calcium chloride was a commercial product complying with

American Society of Resting Materials Standard Specification D 9S~34.

The concrete tested was of a 1:2:4 mix By volume, using local

(District of Columbia) sand and gravel. To the gaging water ( 6.5

gallons per sack) commercial calcium chloride in varying amounts was

added. Standard sand mortar (1:3 mix) and plastic mortars were also

tested. Since it was shown that the use of from 1 l/2 to 2 percent

of commercial calcium chloride (By weight of cement) gave the Best

and most economical results, this digest confines its discussion

chiefly to the effects of calcium chloride in those proportions.

Available from Superintendent of Documents, Government Printing

Office, Washington, D. C. (Price 5 cents)

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050836-2
It was shown on an average that with standard cements at the curing

temperature at 70 ° F without the admixture, initial set took place in

approximately 3 hours and 15 minutes, and the final set in approximately

6 hours, while those same standard cements with 2 percent calcium

chloride reached the initial set in approximately 1 hour and the final

set in approximately 2 hours and ^0 minutes. In general, it was noted

that the average setting time together with the spread of the time of set,

decreased as the amount of calcium chloride increased. The addition of

calcium chloride affected white and high-early-strength cements similarly.

Greater ease of placing and increased workability were noted in both

mortar and concrete with the admixture present.

Since there is a direct relation between the rate of evolution of

heat or temperature rise, and the rate of hardening or set, too great an increase in cither or both may cause a time of .set so rapid that finishing of placed concrete would be difficult.

Effects of curing temperatures on the strength of concrete (based

on plastic mortar cubes) were determined, the early strength decreasing

very markedly as temperatures approached the freezing point. However,

with the addition of calcium chloride it was evident that the lower the

initial curing temperature, the more effective was the calcium chloride

in producing early strength; thus, the proportional effect of adding

calcium chloride is much greater at the lower temperatures.

Construction at low temperatures requires special measures to assure

a rate of hydration of cement that will develop early strength. An added

advantage in using calcium chloride in cold weather is the earlier development of heat. In thin concrete slabs, where the heat may be readily

dissipated, the increased rapidity of heat development will compensate

for some of the heat lost and will decrease, the curing time and time

necessary for the protection of concrete by the use of coverings, etc.

Compressive strength tests conducted .with specimens of mortar with

2 percent calcium chloride and cured at 70 ° F showed at 1 year approxi-

.

mately 15 percent greater strength than plain mortar. The strength at

1 day was practically doubled. Concretes' of standard cements with 2

percent calcium chloride added showed an average strength at 1 day of

128 percent higher than plain concrete, at 28 days 13 percent, at JO days

9 percent, and at 1 year 8 percent. White and high-early-strength

cements were likewise increased in strength.

Based on plastic mortar cubes, effects of curing temperatures and

the addition of calcium chloride on the length of time required for

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1:2:4- concrete to attain a compressive strength, of 2,5^0 pounds per

square inch are shown below.

Cement

Humber of Days

Ta Reach

2500 lbs. per sq. in.

at

Curing Temperatures

4o o P : 70°/ : 90°F

Standard (without admixture)

• 1 • » 14 : 6 : 4

Standard ulus 2tfo commercial calcium chloride S : 3 : Standard plus 1 l/2p commercial calcium chloride : : 2

High-early (without admixture) 5 s 2 : 1

High-early plus 2fo commercial calcium chloride 3 : : High-early plus 1 l/2$ commercial calcium chloride : 1 : 1

• • • «

As indicated by these tests, the proportions of commercial calcium

chloride required for the three curing temperatures studied are:

Temperatures Commercial Calcium Chloride Type of Cement

op Percent

4o 2 All cements

70 2 Normal and white

70 1.5 High-early

90 1-5 All cements

Note: Calcium chloride should be added in proper proportions (by

weight of cement) to the gaging water prior to use.

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