BKICK ROADS. 9 



does not readily absorb water. Not infrequently one of the shoulders 

 is made sufficiently wide to form an earth roadway parallel to the 

 brick pavement. Such an arrangement serves to relieve the pave- 

 ment of considerable traffic during favorable seasons and also affords 

 some advantage to horse-drawn traffic. The general method of con- 

 structing shoulders for brick roads is not essentially different from 

 , that employed for other types of pavements. 



CURBING. 



Brick pavements, as generally constructed, should be supplied wdth 

 strong, durable curbing, both on the sides and at the ends. Otherwise 

 the marginal brick will soon become displaced by the action of 

 traffic, and their displacement will, of course, expose the brick next 

 adjoining, so that deterioration might eventually spread over the 

 entire pavement. Properly constructed curbing, on the other hand, 

 Avill hold the pavement as in a frame and enable the brick to present 

 their combined resistance to the destructive influences of traffic. 



Satisfactory curbs may be constructed of stone, Portland cement 

 concrete, or vitrified clay shapes made especially for this purpose. 

 Wood has also been used for curbs to a limited extent, but when 

 it is considered that the life of a brick pavement under ordinary 

 conditions should far exceed the life of any wood curb which might 

 be devised, the economy of employing a more durable material is 

 readily apparent. 



Stone curbing may be made from any hard, tough stone which is 

 sufficiently homogeneous and free from seams to admit being quar- 

 ried into blocks not less than 4 feet long, 5 inches thick, and 18 

 inches deep. On account of their ordinarily homogeneous struc- 

 ture, granite and sandstone are probably more used for curbs than 

 any other kind of stone. 



All stone curbing should be hauled, distributed, and set before the 

 subgrade is completed. The individual blocks should be not less 

 than about 4 feet long, except at closures, and should ordinarily have 

 a depth of from 16 to 24 inches, depending on soil conditions and on 

 whether the curb is to project above the surface, forming one side 

 of the gutter. The neat thickness need never be greater than 8 

 inches and, where the traffic conditions are not severe and the quality 

 of the stone is good, a thickness of 6 inches will ordinarily prove 

 satisfactory. Stone curb should always be set on a firm bed of 

 gravel, slag, or broken stone, not less than 3 inches thick, or on 

 unusually firm earth, and should be provided with a backing of the 

 same material on the shoulder or sidewalk side. Figure 1 shows a 

 typical stone curb in place. 



Where suitable stone is not readily available or when from any 

 cause the cost of stone curbing would prove excessive, a curb con- 

 40065°— Bull. 373— 16 2 



