SPECIFICATIONS AND TESTS FOR CEMENT Standard Specifications.—The specifications of the American Society for Testing Materials are now commonly recognized as standard and used in the purchase of cement in the United States. These specifications were adopted in 1904 and revised in 1908, 1909, and 1916. In specifications for construction of masonry and concrete it is usual to require that the cement meet the requirements of the American Society, for Testing Materials, although in ordinary work it is not common to actually apply all the tests. The tests of chemical analysis and specific gravity are used only when special reasons exist for their application in the character of the work to which the cement is to be applied or doubt as to the material offered.
It is frequently necessary, on important work, to modify the specifications to suit the peculiarities of the particular construction, This is particularly the case in work to be subjected to the action of sea water, or unusual conditions of service.
The general specifications adopted in 1909 were modified in 1916 as to Portland cement only, those for natural cement being left unchanged. The Committee, however, expressed the intention of proceeding with the modification of the requirements for natural cement as soon as possible, and changes may be expected in these at an early date. The methods of making the tests for Portland are to be also applied to natural cement.
The 1916 specifications make sonic important changes from those previously used. The No. 100 sieve is dropped from the test for fineness and the requirements somewhat increased for the No. 200 sieve. The Gillmore needles are introduced as an alternate method in the test for rate of setting. Tensile tests of cement paste are dropped and sole dependence placed on the 1 to :3 mortar test, requirements for which are somewhat increased. The normal test for soundness which had previously been the final test is dropped and the steam test is made the standard.
The specifications have been gradually developed through experi ence with a number of different methods of testing which have been changed from time to time as knowledge of the material has increased and manufacturers have improved the quality of the material they are able to produce. The reliability of the cement on the market
has markedly improved within a few years past and the likelihood of finding poor cement and consequently the necessity for tests under ordinary circumstances has greatly diminished. The applica tion of tests where feasible and upon all important work is, however, desirable.
The specifications for Portland cement adopted in 1916 are the result of several years' work of a Joint Committee of the American Society of Civil Engineers, the U. S. Government Engineers, and the American Society for Testing Materials. They are published in the Book of Standards of the Society for Testing Materials, and are also reprinted for distribution to those interested in cement testing by the Portland Cement Association.
20. Purpose of Standard tests imposed by the standard specifications are chemical analysis, specific gravity, fine ness, normal consistency, time of setting, tensile strength, and soundness. Specifications covering all of these are usually employed for cement to be used in important work. The making of the tests for chemical analysis and specific gravity are often omitted when the cement proves satisfactory upon the other tests.
The chemical analyses employed for Portland cement are intended to determine whether the cement has been adulterated with inert material, such as slag or ground limestone, and whether magnesia or sulphuric anhydride are present in too large amounts.
The test for specific gravity when used for Portland cement is intended mainly to detect adulteration with materials of lower specific gravity. It may also aid in determining the true character of the material and whether the cement is well burned. The specific gravity of Portland cement is usually between 3.10 and 3.20, that of a natural cement 2.75 to 3.10, and puzzolan cement 2.7 to 2.9. Good Portland cement may he lowered in specific gravity by long exposure to the air without serious injury to the cement. For this reason, the specifications allow a second test upon an ignited sample of cement failing upon a first test.