26 
BULLETIN 704, U. S. DEPARTMENT OF AGRICULTURE. | 
3. Grading of gravel and sand, U. S. Department of Agriculture Bulle- 
Wun BM, 1, ster 
4. Strength test of sand, U. S. Department of Agriculture Bulletin 555, 
105 BY, 
5. Elutriation test of sand, A. S. T. M. Standard, C9-17. 
This specification covers granite block, cushion sand, grouting 
sand, and gravel filler to be used in the construction of a stone- 
block wearing 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 well 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 13 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 before 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. 
