60. Definition

This term shall be applied to the finely pulverized product resulting from the calcination of an argillaceous limestone at a temperature only sufficient to drive off the carbonic acid gas.

61. Specific Gravity

The specific gravity of the cement thoroughly dried at 100° C.; shall be not less than 2.8.

62. Fineness

It shall leave by weight a residue of not more than 10 per cent on the No. 100, and 30 per cent on the No. 200 sieve.

63. Time Of Setting

It shall develop initial set in not less than ten minutes, and hard set in not less than thirty minutes, nor more than three hours.

64. Tensile Strength

The minimum requirements for tensile strength for briquettes one inch square in cross-section, shall be within the following limits, and shall show no retrogression in strength within the periods specified:

Neat Cement

Age

Strength

24 hours in moist air..

50-100

lbs.

7 days (1 day in moist air, 6 days in water).

100-200

,,

28 days (1 day in moist air, 27 days in water).

200-300

,,

One Part Cement, Three Parts Standard Sand

7 days (1 day in moist air, 6 days in water).

. 25- 75

,,

28 days (1 day in moist air, 27 days in water).

. 75-150

,,

6o. Constancy of Volume. rats of neat cement about three inches in diameter, one-half inch thick at the center, and tapering to a thin edge, shall be kept in moist air for a period of twenty-four hours.

(a) A pat is then kept in air at normal temperature.

(b) Another is kept in water maintained as near 70° F. as practicable.

These pats are observed at intervals for at least 28 days, and, to pass the tests satisfactorily, should remain firm and hard and show no signs of distortion, cracking, or disintegrating.