88 HIGHWAY CONSTRUCTION 



this are: (1) To prevent the .traffic crossing the intersection from 

 following the longitudinal joints and thus forming depressions and 

 ruts; (2) Laid in this rranner, the blocks afford a more secure foot- 

 hold for horses turning the corners. The ends of the diagonal blocks 

 where they abut against the straight blocks, must be cut to the re- 

 quired bevel. 



The blocks forming each course must be of the same depth, and 

 no deviation greater than one-quarter of an inch should be permitted. 

 The blocks should be assorted as they are delivered, and only those 

 corresponding in depth and width should be used in the same course. 

 The better method would be to gauge the blocks at the quarry. 

 This would lessen the cost considerably ; it would also avoid the in- 

 convenience to the public due to the stopping of travel because of the 

 rejection of defective material on the ground. , This rnethod would 

 undoubtedly be preferable to the contractor, who would be saved the 

 expense of handling unsatisfactory material ; and it would also leave 

 the inspectors free to pay more attention to the manner in which the 

 work of paving is performed. 



The accurate gauging of the blocks is a matter of much impor- 

 tance. If good work is to be executed, the blocks, when laid, must be 

 in parallel and even courses ; and if the blocks be not accurately gauged 

 to one uniform size, the result will be a badly paved street, with the 

 courses running unevenly. The cost of assorting blocks into lots of 

 uniform width, after delivery on the street, is far in excess of any ad- 

 ditional price which would have to be paid for accurate gauging at the 

 quarry. 



Foundation. The foundation of the blocks must be solid and 

 unyielding. A bed of hydraulic-cement concrete is the most suitable, 

 the thickness of which must be regulated according to the traffic ; the 

 thickness, however, should not be less than 4 inches, and need not be 

 more than 9 inches. A thickness of 6 inches will sustain traffic of 600 

 tons per foot of width. 



Cushion Coat. Between the surface of the concrete and the base 

 of the blocks, there must be placed a cushion-coat formed of an incom- 

 pressible but mobile material, the particles of which will readily adjust 

 themselves to the irregularities of the bases of the blocks and transfer 

 the pressure of the traffic uniformly to the concrete below. A kyer 

 of dry, clean sand 1 to 2 inches thick forms an excellent cushion-coat. 



