(a) An analysis of the combined materials must come within the following limits:
Bitumen, 6 to 9 percent.
Crushed stone or gravel passing 1¼-inch mesh and retained on ¼-inch mesh, 35 to 45 percent.
Crushed stone or gravel passing a ½-inch screen and retained on 10-inch mesh, 25 to 40 percent.
The balance of the aggregates, from 20 to 35 percent, must be composed of sand and fine material, graded approximately as specified in section 17-89.
(b) The stone and sand shall be dried and heated in properly designed driers before mixing with the asphaltic cement. They shall be of the revolving type, turning the materials during the process of drying.
(c) When the aggregates are thoroughly dried and heated to a temperature of from 250 to 350 degrees Fahrenheit, arranged so the heat can be properly and easily controlled and regulated, the stone and sand aggregates and asphaltic cement must be weighed carefully and dumped directly from weighing boxes into the mixing hopper and mixed until the asphaltic cement is thoroughly and uniformly distributed, so that each particle of sand and stone is thoroughly and uniformly distributed, and so that each particle of sand and stone is thoroughly coated with the asphaltic cement.