404 ROADS AND PAVEMENTS 



the length from 9 to 12 in. The blocks must be rammed with a 

 ram weighing not less than 50 Ib. The joints between the blocks 

 must be filled with an impervious material, for which the most 

 suitable is bituminous concrete composed of asphaltic cement 

 and gravel. In applying this filling, the joints should be first 

 filled with gravel to a depth of about 2 in. ; then the hot pitch 

 should be poured in, filling the joints to the depth of about 1 in. 

 above the gravel; then the gravel and pitch should be added 

 alternately until the joints are filled to within $ in. of the top; 

 the remainder should then be completely filled with pitch 

 over which fine gravel should be sprinkled. The joint thus 

 formed is impervious to moisture; it adds considerably to 

 the strength of the pavement and makes it less noisy. 



Stone-block pavements are very durable and economical, 

 are easily accessible for repairs and afford a good foothold for 

 horses; on the other hand, they have considerable tractive 

 resistance and are very noisy. 



Wooden-Block Pavements. The best, as well as the simplest, 

 form of wooden pavements consist of rectangular or cylindrical 

 blocks that are set on a solid foundation with the fibers vertical 

 and have the joints thus formed filled with an impervious 

 cement. Hydraulic-cement concrete forms the best foundation. 

 A cushion coat composed either of dry sand, hydraulic-cement 

 mortar, or asphaltic cement i in. thick is spread over the con- 

 crete in which the blocks are embedded. Rectangular blocks 

 are generally required to be 3 in. in width, 6 in. in depth, and 

 about 9 in. in length; cylindrical blocks, from 4 to 8 in. in 

 diameter and 6 in. in depth. Each block should be of uniform 

 cross-section throughout its length, with its ends truly per- 

 pendicular to its axis. After the blocks have been rammed 

 properly, the joints must be filled with Portland-cement grout; 

 or, a better result is obtained by filling the lower 2 or 3 in. with 

 bituminous cement and the remainder with hydraulic-cement 

 grout. In cylindrical-block pavements, it is advantageous 

 to add gravel to the bituminous cement in order to fill the large 

 spaces between the blocks. 



The most suitable woods for pavement are not the hardwoods 

 but close-grained pitchy soft woods. These wear longer than 

 the hardwoods, and afford a better foothold for horses. Chem- 



