26 BULLETIN 701, TJ. S. DEPARTMENT OF AGRICULTURE. 



3. Grading of gravel and sand. U. S. Department of Agriculture Bulle- 



tin 555, p. 33. 



4. Strength test of sand. U. S. Department of Agriculture Bulletin 555, 



p. 32. 



5. Elutrlation test of sand, A. S. T. M. Standard, C9-17. 



This specification covers granite blocli, cusliion sand, grouting 

 sand, and gravel filler to be used in the construction of a stone- 

 block \\earing course and sand cushion. 



The requirements for quality of block here given are on the 

 basis of a pavement subjected to comparatively moderate traffic. 

 For very heavy traffic, a French coefficient of wear of 10.0 or 11.0 

 and a toughness of 9 or 10 may reasonably be required. While a 

 coefficient of hardness of not less than 16 might vi^ell be included 

 under physical properties, a requirement for French coefficient of 

 wear has been used instead, owing to the fact that but few 

 laboratories are equipped with a Dorry hardness machine. 



The sand cushion, or sand cement cushion, should be placed 

 upon a concrete foundation to a depth of from 1 to 1^ inches and 

 should be carefully shaped to the cross section of the finished 

 pavement at such a height that the blocks after consolidation 

 are at grade. The blocks are usually laid in straight rows at 

 right angles to the curb, with joints broken at least 3 inches, and 

 are rammed to a solid bearing befoi'e filling. Joints in block 

 pavements may be filled with either a cement grout, bituminous 

 mastic, or gravel with a poured bituminous filler. Grouting sand 

 as called for in this specification may be used with either Port- 

 land cement to form the sand-cement grout, or a bituminous ma- 

 terial to form a bituminous mastic. If a gravel and bituminous 

 filler is to be used the requirements for grouting sand and all 

 reference thereto should be eliminated from the specifications. 



