HIGHWAY CONSTRUCTION 95 



true and parallel planes. If this is not done, they should he hedded, 

 while in the testing machine, in plaster of Paris, which should be 

 allowed to harden ten minutes under weight of the crushing planes 

 only, before the load is applied. 



3. The load should be applied at a uniform rate of increase to 

 the point of rupture. 



4. Not less than an average obtained from five tests on five 

 different bricks shall constitute a standard test. 



Properties of Paving Bricks. Paving bricks range in weight 

 from 5 to 7-j pounds; in specific gravity, from 1.91 to 2.70; in resist- 

 ance to crushing, from 7,000 to 18,000 pounds per square inch; in 

 resistance to cross-breaking, II = 1 ,400 to 2,000 pounds ; in absorption, 

 from 0.15 to 3 per cent in 24 hours. The dimensions vary according to 

 locality and the requirements of the specifications. The "standard" 

 bricks are 2^ X 4 X 8 inches, requiring 58 bricks to the square yard, 

 and weighing 7 pounds each ;" repressed", 2 J X 4 X8i inches, requir- 

 ing 61 to the square yard, and weighing 6i pounds each; "Metropoli- 

 tan", 3X4X9 inches, requiring 45 to the square yard, and weighing 

 9J pounds each. 



Advantages of Brick Pavements. These may be stated as follows : 



(1) Ease of traction. 



(2) Good foothold for horses. 



(3) Not disagreeably noisy. 



(4) Yields but little dust and mud. 



(5) Adapted to all grades. 



(6) Easily repaired. 



(7) Easily cleaned. 



(8) But slightly absorbent. 



(9) Pleasing to the eye. 



(10) Expeditiously laid. 



(11) Durable under moderate traffic. 



Defects of Brick Pavements. The principal defects of brick 

 pavements arise from lack of uniformity in the quality of the bricks, 

 and from the liability of incorporating in the pavement bricks of too 

 s.)ft or porous a structure, which crumbles under the action of traffic 

 or frost. 



Foundation. A brick pavement should have a firm foundation. 

 As the surface is made up of small, independent blocks, each one must 



