(a) The ingredients for the asphalt wearing surface shall be asphalt cement, sand, portland cement or dust in the following proportions:
Bitumen, 8 to 11 percent.
Total passing 200-mesh sieve, not less than 10 percent.
Total passing 80-mesh sieve, 20 to 35 percent.
Total passing 40-mesh sieve, 45 to 60 percent.
Total passing 8-mesh sieve, 99 to 100 percent.
(b) The minimum amount of bitumen shall be used only in mixtures containing the minimum total, passing the 80-mesh sieve. The percentage of bitumen must be increased above the minimum as the total passing the 80-mesh sieve increases.
(c) The above limits as to mesh composition and percentage of bitumen are intended to provide for such permissible variations as may be deemed necessary by the character and location of the work to be done. When the materials which are to be used have been tested, and the proper grading secured, no variation is to be made, except with the consent of, or at the direction of the urban county engineer.