58. Constancy of Volume. The object is to develop those quali ties which tend to destroy the strength and durability of a cement. As it is highly essential to determine such qualities at once, tests of this character are for the most part made in a very short time, and are known, therefore, as accelerated tests. Failure is revealed by crack ing, checking, swelling, or disintegration, or all of these phenomena. A cement which remains perfectly sound is said to be of constant volume.
Methods. Tests for constancy of volume are divided into two classes: (1) Normal tests, or those made in either air or water maintained at about 21° Cent. (70° Fahr.).
(2) Accelerated tests, or those made in air, steam, or water at a temperature of 45° Cent. (115° Fahr.) and upward. The test pieces should be allowed to remain 24 hours in moist air before immersion in water or steam, or preservation in air. For these tests, pats, about cm. (2.05 in.) in diameter, 1} cm. (0.49 in.) thick at the center, and tapering to a thin edge, should be made, upon a clean glass plate [about 10 cm. (3.94 in.) square], from cement paste of normal consistency.
Normal Test. A pat is immersed in water maintained as near 21° Cent. (70° Fahr.) as possible for 2S days, and observed at inter vals. A similar pat is maintained in air at ordinary temperature and observed at intervals.
Accelerated Test. A pat is exposed in any convenient way in an atmosphere of steam, above boiling water, in a loosely closed vessel, for 3 hours.
To pass these tests satisfactorily, the pats should remain firm and hard, and show no signs of cracking, distortion, or disintegration. Should the pat leave the plate, distortion may be detected best with a straight-edge applied to the surface which was in contact with the plate. In the present state of our knowledge it cannot be said that
cement should necessarily be condemned simply for failure to pass the accelerated tests; nor can a cement be considered entirely satis factory, simply because it has passed these tests.
59.* General Conditions. The committee recommends that: All cement shall be inspected.
Cement may 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.
The cement shall be stored in such a manner as to permit easy access for proper inspection and identification of each shipment.
Every facility shall be provided by the contractor, and a period of at least twelve days allowed for the inspection and necessary tests.
Cement shall be delivered in suitable packages, 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 requirements may be held awaiting the results of the 2S-day tests, before rejection.
All tests shall be made in accordance with the methods proposed by the Committee on Uniform Tests of Cement of the American Society of Civil Engineers, presented to the Society January 21, 1903, and amended January 20, 1904, with all subsequent amendments thereto.
The acceptance or rejection shall be based on the following re quirements: * Paragraphs 59 to inclusive were taken from the report of a Committee of the American Society for Testing Materials.