SPECIFICATIONS FOR NONBITUMINOUS ROAD MATERIALS. 
Tests of the grading or mechanical analysis of broken stone or gravel, Methods of 
and sand, and of the mortar tensile strength of sand shall be made in Testing. 
accordance with the following methods: 
1. Grading of broken stone or gravel, U. S. Department of Agriculture 
Bulletin 555, p. 32. (8) 
2. Mechanical analysis of sand, U. S. Department of Agriculture Bulle- 
tin 555, p. 33. 
3. Elutriation test for sand, U. S. Department of Agriculture Bulletin 
HN, 105 B74. 
4. Mortar tensile strength test for sand, A. 8S. T. M., Standard Test 
C9-17. 
This specification provides for coarse and fine aggregate to be 
used in the construction of a Portland cement concrete base. 
The 15 per cent of coarse aggregate passing the 4-inch screen 
which is allowed is only permissible upon the assumption that con- 
struction specifications will be based upon a fixed proportion of 
cement to combined coarse and fine aggregate and that the relative 
amounts of broken stone or gravel and sand will be varied as 
directed by the enginer so as to approximate definite proportions 
of coarse and fine aggregate. Thus the concrete should be com- 
posed of 1 part of Portland cement and 9 parts of fine and coarse 
aggregate, each measured separately and accurately by volume. 
The concrete should approximate a 1:3:6 mix, but the engineer 
should vary the relative proportions of fine and coarse aggregate 
depending upon their exact grading, so as to obtain a concrete of 
maximum density. 
The concrete should be mixed in a batch mixer for not less than 
1 minute and the water should be reasonably clear, free from oil, 
acid, alkali, or vegetable substance, and neither brackish nor salt. 
Sufficient water should be used to produce a concrete which will 
flatten out and quake when deposited in place, but not enough to 
cause it to flow or to separate mortar and coarse aggregate. 
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