94 HIGHWAY CONSTRUCTION 



5. After soaking, and before weighing, the bricks must be wiped 

 dry from surplus water. 



6. The difference in the weight must be determined on scales 

 sensitive to one gram. 



7. The increase in weight due to water absorbed shall be cal- 

 culated in per cents of the initial dry weight. 



Cross=Breaking Test 



1. Support the brick on edge, or as laid in the pavement, on 

 hardened steel knife-edges, rounded longitudinally to a radius of 

 twelve inches and transversely to a radius of one-eighth inch, and 

 bolted in position so as to secure a span of six inches. 



2. Apply the load to the middle of the top face through a hard- 

 ened steel knife-edge, straight longitudinally and rounded transversely 

 to a radius of one-sixteenth inch. 



3. Apply the load at a uniform rate of increase till fracture 

 ensues. 



4. Compute the modulus of rupture by the formula 





 ' 



in which / = modulus of rupture, in pounds per square inch; 

 w = total breaking load, in pounds; 

 / = length of span, in inches =6; 

 b = breadth of brick, in inches- 

 d = depth of brick, in inches. 



5. Samples for test must be free from all visible irregularities of 

 surface or deformities of shape, and their upper and lower faces must 

 be practically parallel. 



6. Not less than ten brick shall be broken, and the average of all 

 shall be taken for a standard test. 



Crushing Test 



1. The crushing test should be made on half-bricks, loaded 

 edgewise, or as they are laid in the street. If the machine used is 

 unable to crush a full half-brick, the area may be reduced by chipping 

 off, keeping the form of the piece to be tested as nearly prismatic as 

 possible. A machine of at least 100,000 pounds' Capacity should be 

 used; and the specimen should not be reduced below four square 

 inches of area in cross-section at right angles to direction of load. 



2. The upper and lower surfaces should preferably be ground to 



