﻿8 BULLETIN 23, U. S. DEPARTMENT OF AGRICULTURE. 



Good paving brick will ordinarily lose from 17 per cent to 22 per 



cent of their original weight in the rattler test, and specifications 



concerning this loss should be prepared with a view to the character 



of the traffic for which the pavement is designed. Some reasonable 



requirement as to the loss sustained by any individual brick should 



also be made. This loss should ordinarily not exceed 25 per cent, 



and under severe traffic conditions a smaller percentage should be 



required. 



CONSTRUCTION. 



PREPARING THE SUBGRADE. 



In forming a roadbed upon which a brick pavement is to be con- 

 structed, the essential features to be considered are (1) thorough 

 drainage, (2) firmness, (3) uniformity in grade and cross section, and 

 (4) adequate shoulders. 



Thorough drainage can be secured for any particular road only by 

 means of a careful study of the local conditions which affect the 

 accumulation and " run-off" of both the surface and ground water. 

 These conditions vary considerably even in the same locality, and no 

 set of rules can be given which would cover all cases. For example, 

 the material composing the roadbed may be springy, and in this case 

 tile underdrains will probably be necessary. On the other hand, 

 extremely flat topography may make it necessary to elevate the 

 grade considerably above the surrounding land. The nature of the 

 soil, the topography, and the rainfall must all be considered if a sys- 

 tem of drainage is to be planned properly. 



The second requirement, firmness, can be secured only after the 

 road has been properly drained. Soils which readily absorb moisture 

 can not be properly drained in wet weather and should not be per- 

 mitted to form a part of the subgrade. In order that the subgrade 

 may be unyielding, it is also necessary that the roadbed be thoroughly 

 compacted. In forming embankments, the material should be put 

 down in layers not over 8 inches thick, and each layer should be 

 thoroughly rolled. In excavation care should be exercised, if the 

 material is earth, not to permit plows or scrapers to penetrate below 

 the subgrade. The subgrade in both excavation and embankment 

 should be brought to its final shape by means of finish grading 

 with picks and shovels and rolling. 



When completed the subgrade should be uniform in grade and 

 cross section, or otherwise the foundation must be made unneces- 

 sarily thick where depressions occur, in order that its grade and 

 cross section may be uniform and its thickness not less at any point 

 than that required. The subgrade should be repeatedly rolled and 

 reshaped until the desired shape is secured. The curbs, which 

 should be set before the final finishing, may be made to serve as a 

 guide for this work. 



