Standard Specifications for Cement

STANDARD SPECIFICATIONS FOR CEMENT The requirements which a cement must meet in order to be recognized as of "standard" quality, are outlined by the Committee on Standard Specifications for Cement, of the American Society for Testing Materials, in substance as follows: General Conditions. All cement shall be inspected—either at the place of manufacture or on the work.

In order to allow ample time for inspecting and testing, the cement should be stored in a suitable weather-tight building having the floor properly blocked or raised from the ground, and should be easy of access for proper inspec tion and identification of each shipment.

Every facility shall be provided by the con tractor, and a period of at least twelve days allowed for the inspection and necessary tests.

Cement shall be delivered in suitable pack ages, with the brand and name of manufacturer plainly marked thereon.

A bag of cement shall contain 94 pounds of cement, net. Each barrel of Portland cement shall contain 4 bags, and each barrel of natural cement shall contain 3 bags of the above net weight.

Cement failing to meet the 7-day require ments may be held awaiting the results of the 28-day tests before rejection.

All tests shall be made in accordance with the methods proposed by the Committee on Uni form Tests of Cement, of the American Society of Civil Engineers (see above).

The acceptance or rejection' shall be based on the following requirements: Specifications for Natural Cement Fineness. A natural cement 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.

Time of Setting. It shall not develop initial set in less than 10 minutes, and shall not develop hard set in less than 30 minutes, or in more than 3 hours.

Tensile Strength.

The minimum require ments 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: For example, the minimum requirement for the 24-hour neat cement test should be some specified value within the limits of 50 and 100 pounds; and so on for each period stated.

If the minimum strength is not specified, the mean of the above values shall be taken as the minimum strength required.

Constancy of Volume.

Pats of neat cement about three inches in diameter, one-half inch thick at center, tapering to a thin edge, shall be kept in moist air for a period of 24 hours. One pat shall then be kept in air at normal tempera ture; and another kept in water maintained as near 70 degrees F. as practicable.

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

Specifications for Portland Cement Specific Gravity. The specific gravity of the cement, ignited at a low red heat, shall be not less than 3.10, and the cement shall not show a loss in weight, on ignition, of more than 4 per cent.

To determine the loss on ignition, place half a gram of cement in a platinum crucible, set in a hole in an asbestos board so that about three fifths of the crucible projects below the board. Expose the crucible to blast flame for 15 min utes, preferably with an inclined flame. The loss, found on weighing, should be checked by a second blasting of 5 minutes.

Fineness. The cement shall leave by weight a residue of not more than 8 per cent on the No. 100, and not more than 25 per cent on the No. 200 sieve.

Time of Setting. It shall not develop initial set in less than 30 minutes, and must develop hard set in not less than 1 hour, nor more than 10 hours.

Tensile Strength.

The minimum require ments for tensile strength for briquettes one inch square in section, shall be within the fol lowing limits, and shall show no retrogression in strength within the periods specified: For example, the minimum requirement for the 24-hour neat cement test should be some specified value within the limits of 150 and 200 pounds; and so on for each period stated.