ROADS AND PAVEMENTS 405 



ical treatments of paving blocks have very little effect on the 

 wearing properties of the wood, and their use is of doubtful 

 economic value. Blocks not treated chemically expand in the 

 direction perpendicular to the fibers about 1 in. in 8 ft. Wood 

 attains the full amount of expansion in from 12 to 18 mo. Pro- 

 vision must be made for this either by leaving the joints near 

 the curbs temporarily open or by omitting the course near the 

 curbs. The pavement is finished properly after the expansion 

 has ceased. 



Brick Pavements. When constructed in a proper manner 

 and of suitable materials, brick pavements form a smooth 

 durable surface that is well adapted to moderate traffic. Bricks 

 suitable for paving should not contain more than 1% of lime, 

 and should be burned specially for the purpose. When tested 

 on their flat sides, they should offer a resistance to crushing of 

 not less than 8,000 Ib. per sq. in. They should not absorb 

 more than 5% of their weight of water, and should be so tough 

 that, when struck a quick blow on the edge with a 4-lb. hammer, 

 the edge will not spall or chip. The bricks should be of uniform 

 size, straight, square on edges, and free from fire-cracks or 

 checks. When broken, the fracture should appear smooth and 

 the texture uniform, and when struck together, the pieces should 

 have a firm, metallic ring. 



Many methods of construction have been tried. The best 

 modern practice is to use a hydraulic-cement foundation, con- 

 structed as described for granite-block pavements. On this 

 foundation a layer of fine, clean, dry sand should be spread to a 

 uniform depth of -J in., as a cushion coat to receive the bricks.. 

 It is essential that the sand for the cushion coat should be per- 

 fectly free from moisture; if necessary, it should be dried by 

 artificial heat. The cushion coat is sometimes made as deep 

 as 2 in. 



After the brick has been properly laid, it should be sprinkled 

 with water for about 15 min., the water being applied from a 

 hose or can fitted with a rose spray. Shortly after the sprink- 

 ling, the surface of the pavement should be inspected, and all 

 the bricks that appear wet or damp should be removed and 

 replaced with new bricks. The bricks are then pressed with a 

 light hand hammer, after which they are thoroughly rammed 



