HIGHWAY CONSTRUCTION 



91 



blocks will be jtirral loose, the surface of the pavement I rooming a 

 series of ridges and hollows. 



The quantity of cement required per square yard of pavement will 

 vary according to the shape of the blocks, the width of the joints, and 

 the depth of the sand bed. With well-shaped blocks, close joints, and 

 a half-inch sand bed, the quantity will vary from 3V to 5 gallons; with 

 ill-shaped blocks, wide joints, and a heavy sand bed, 10 to 12 gallons 



Fig. 57. 



would not be an excessive amount to use to secure the result obtained 

 by employing well-shaped blocks and close joints. 



Stone Pavement on Steep Grades. Stone blocks may be em- 

 ployed on all practicable grades; but on grades exceeding 10 per cent, 

 cobblestones afford a better foothold than blocks. The cobblestones 

 should be of uniform length, the length being at least twice the breadth 

 say stones 6 inches long and 2^ to 3 inches in diameter. These 

 should be set on a concrete foundation, laid stone to stone, and the 



Fig. 58. 



interstices filled with cement grout or bituminous cement; or a bitu- 

 minous concrete foundation may be employed and the interstices l>e- 

 tween the stones filled witli asphaltic paving cement. Should stone 

 blocks be preferred, they must be laid, when the grade exceeds 5 per 

 cent, with a serrated surface, by either of the methods shown in Figs. 

 57 and 58. The method shown in Fig. 57 consists in slightly tilting 

 the blocks on their bed so as to form a series of ledges or steps, against 

 which the horses' feet being planted, a secure foothold is obtained. 

 The method shown in Fig. 58 consists in placing between the rows of 



