138 The concrete shall be composed of cement, sand, and coarse material in one of the following or intermediate proportions, and the ultimate compressive resistance shall not be less than that specified for the proportion adopted.

139 For determining the resistance of concrete, tests shall be made on cubes of not less than 4 inches each way, or cylinders of not less than 6 inches each way.

140 The conditions accompanying the preparation, setting, maturing, and actual testing of the cube or other test piece shall as far as possible conform to the conditions that would obtain in the actual execution of the reinforced work.

141 The ultimate compressive resistance of concrete f materials mixed in intermediate proportions may be estimated from the following equation.

142 All three materials shall be thoroughly mixed dry, and then thoroughly mixed again after wetting subject to the requirements of the regulation numbered 134 Salt water shall not be used for the concrete.