SPECIFICATIONS FOR NONBITUMINOUS EOAD MATERIALS. 15 



Tests of the grading or mechanical analysis of brolfen 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, TJ. 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 



555, p. 32. 



4. Mortar tensile strength test for sand, A. S. T. M., Standard Test 



C9-17., 



This specification provides for coarse and fine aggregate to be 

 used in tlie construction of a Portland cement concrete base. 



Tlie 15 per cent of coarse aggregate passing tlie i-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. 



