BRICK ROADS. 



COLOR. 



The color is a valuable guide in inspecting brick from the same 

 plant, but it is of little importance when the brick to be compared 

 are from different factories. For brick manufactured from a partic- 

 ular raw material the color indicates, in a measure, the temperature 

 to which they have been subjected, provided they have been burned 

 under identical conditions. Ordinarily, the darker the color the 

 higher the temperature, and, presumably, the better the brick. The 

 surface color of brick may be very misleading, however, and the color 

 of the interior should be used in making comparisons. 



SPECIFIC GRAVITY. 



The specific gravity of paving brick was formerly considered of 

 importance in judging their fitness for use in pavements. But it has 

 since been generally conceded that a knowledge of the specific gravity 

 is of comparatively little value. The specific gravity of shale brick 

 is ordinarily between 2.20 and 2.40, and of fire-clay brick between 

 2.10 and 2.25. 



ABSORPTION. 



The absorptive power of brick, like their color, is a matter of very 

 slight importance, except for comparing specimens manufactured 

 under identical conditions. It is true that the porosity of the brick 

 increases with the power of absorption, but it is very doubtful if any 

 paving brick possessing an objectionably high absorptive power could 

 pass even a very casual inspection. In other words, a high degree of 

 porosity always manifests itself in other ways more clearly than in 

 the ability of the brick to absorb water. 



CRUSHING STRENGTH. 



The crushing strength of good paving brick varies from 10,000 

 pounds to 20,000 pounds per square inch when the load is applied 

 uniformly over the entire top surface of the test specimen, and may 

 be much greater if the area over which the load is applied is less than 

 that of the top surface. Since paving brick in use are seldom required 

 to withstand a pressure of more than about 2,000 pounds per square 

 inch, and since inferior brick may possess relatively very high resist- 

 ance to crushing, a knowledge of the crushing strength is clearly of 

 little value in comparing the relative excellence of different makes of 

 brick. It is, therefore, usually considered unnecessary to specify a 

 definite requirement as to the crushing strength of paving brick. 



TESTING THE BRICK. 



Definite methods of testing paving brick have been in general use 

 for only a comparatively few years and have only recently undergone 

 a pronounced change. The object of all tests is to determine whether 



