The sand aggregate must be coarse, clean, sharp sand, equal to Ohio River Wash Sand. When dry, eighty-five (85) percent shall pass a one-eighth-inch screen, and not more than two (2) percent by weight of hundred-mesh sieve. It shall contain not more than five (5) percent by weight of lime or other foreign substance. When three (3) parts of the sand are mixed with one (1) part of cement, the tensile strength at the age of seven (7) and twenty-eight (28) days shall be not less than one hundred (100) percent of the strength of the same cement and Ottowa sand.