a, briquets stored in water in laboratory, b to f, inclusive, briquets stored in open air after twenty-four hours in air of laboratory.

a and 6, fresh water used for gaging mortar.

c, d, e and f, water used in gaging had 5, 10, 15 and 25 per cent, salt, respectively.

392. Effect Of Salt In Mortars Hardened In Water And Air

In the tests recorded in Table 105 the materials used were at a temperature of forty degrees Fahr., and the briquets were molded in an open warehouse where the temperature was usually below twenty-three degrees Fahr., though for a few of the tests the temperature of the air at time of molding was as high as twenty-seven degrees. The temperature of the mortar when briquets were finished was usually but little above thirty-two degrees Fahr. The briquets were left in a warehouse for three days, when part of them were immersed in cold water (under ice), and the remainder stored in open air on a shelf covered by a rough board roof, but with front left open to the weather. All mortars contained two parts river sand to one of cement by weight. The water used in gaging varied from fresh to a twenty-five per cent, solution.

Table 105. The Use Of Portland Cement Mortar In Freezing Weather

Mortar

2 parts "Point aux Pins " (river sand), passing No. 10 sieve, to 1 part cement, Portland Brand R. Each result, mean of five specimens. Canal and open air briquets made by different molders.

The results indicate that Portland mortars made in low temperatures, to be immersed in cold water, are improved by fifteen to twenty per cent, salt in the water of gaging, but that more than five per cent, salt is deleterious for mortars exposed to the air only. The very high results given by the air-hardened specimens are worthy of notice.

A similar series of tests of natural cement gave results from which no definite general conclusions could be drawn. The effect of freezing and of the use of salt varied greatly for different samples. For any given sample the treatment, as regards the use of salt, giving good results in open air, was usually the reverse of that giving good results in cold water. The conclusions indicated for rich mortars were sometimes the reverse of those shown by lean mortars.

393. The results obtained with five brands of natural cemerit are given in Table 106. The briquets were made in a temperature of nine to nineteen degrees Fahr. Half of the briquets were made with fresh water, and half with water containing enough salt to lower its freezing point below that of the air where the briquets were made. The results are chiefly of interest as showing the strength that may be attained by natural cement mortars under these severe conditions.

Table 106. Effect Of Low Temperatures On Five Brands Of Natural Cement

Note.— All briquets broken when six and a half months old.

Table 107. Portland Cement Mortar In Low Temperatures Effect Of Heating Materials

Notes.— Cement, Portland. Sand, " Point aux Pins".

When warm materials used, the temperature mortar after briquets finished, 63° to 71° Fahr. When cold materials used, the temperature mortar after briquets finished, 32° to 39° Fahr. When salt water used for mixing, water was 23 per cent, salt for 1 to 1 mortars and 14 per cent, salt for 1 to 2 mortars. Briquets stored in canal were left in cold air three days before immersion.

Part of briquets stored in open air were immersed in tank in laboratory one week just before breaking, while others were broken dry as indicated.

In general, each result is mean of five briquets.

Higher results are usually given by the air-hardened specimens than by those immersed in cold water, though this depends somewhat upon the brand. Salt is usually beneficial if the briquets are immersed, and detrimental for open air exposure.

394. Effect Of Heating The Materials

The tests in Table 107 were made to determine the effect of heating the materials when working in low temperatures, and thus delaying for a time the freezing of the mortars. The details of the tests are fully given in the table. The conclusion indicated is that the ingredients may be used cold or warm indifferently. A gain of only four per cent, is indicated for warm materials in mortars mixed with salt water and hardened in cold fresh water. In practical work, however, the use of warm materials may so delay the freezing as to permit thorough tamping before the mortar freezes. Table 108 gives similar results with one brand of natural cement, from which it appears that warm materials have a slight advantage for either cold water or cold air. hardening.

Table 108. Natural Cement Mortars In Freezing Weather Effect Of Heating Materials

Notes. — Cement, Brand Gn, Natural. All mortars made with fresh water.

Briquets made with warm materials were frozen in from 15 to 24 minutes after made. Each result, mean of ten briquets.

395. Consistency Of Mortars To Withstand Frost

Since the injury due to frost is caused by the expansion of the water used in gaging, it would be expected that mortars mixed wet would suffer most. This conclusion is confirmed by the tests in Table 109. The superiority of dry mortars is especially shown in mortars that harden in the air. The treatment to which these briquets were subjected was very severe, yet the results are excellent.

Table 109. Consistency Of Mortars As Affecting Ability To Withstand Low Temperatures

Notes. — Cement, Portland, Brand R; sand, " Point aux Pins," passing holes .08 inch sq. Two parts sand to one cement by weight. Each result, mean of five briquets. Temperature, air where briquets were molded, 13° to 14° Fahr.; materials used, 40° Fahr. Temperature mortar when molding completed 32° to 36° Fahr. Briquets made with fresh water had frozen after 30 minutes. Treatment briquets: — a to d, stored in canal (under ice).