140. In testing the strength of cement the object is threefold : 1st, to obtain an idea of the strength that may be expected from the cement as used in the structure; 2d, to obtain a basis for comparing the value of different cements in this regard; and 3d, to determine the ability of the cement to withstand destructive agencies, whether these agencies be due to exterior causes or emanate from the character of the cement itself. To illustrate the last point it is only necessary to mention such destroying agents as free lime (interior) and frost (exterior). It is evident that the stronger the cement the more effectually will these agencies be resisted.

The strength of cement may be tested by compression, shearing, bending, adhesion, abrasion and tension. The tensile test is the one most frequently used, but the tests will be considered in the order named.