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BULLETIN 23, U. S. DEPAKTMENT OE AGKICULTURE. 



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

 structed of Portland cement concrete may frequently be advan- 

 tageously used. Concrete curbs may be constructed alone or in com- 

 bination with either a concrete gutter or a concrete foundation. 

 The advisability of constructing the curb in combination with 

 the foundation, however, is doubtful. Very little is saved by such 

 an arrangement, and the small saving is probably even more than 

 offset by the additional difficulty involved in preparing the subgrade 



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Fig. 1. — Proper method of constructing stone curb. 



without the curb to serve as a guide. Concrete curbs should have 

 approximately the same cross-sectional dimensions as stone curbs 

 and should be constructed in sections not exceeding about 7 or 8 feet 

 in length. Figures 2 and 3 and Plate I show the three common 

 methods of constructing concrete curbs. 



. Vitrified clay curbing should be set in much the same manner as 

 that described for stone curbing. The principal additional require- 

 ment is that, since vitrified clay is a lighter material than stone and 

 the curb sections are ordinarily shorter, the bedding must be made 

 correspondingly more secure in order to prevent displacement. 



THE FOUNDATION. 



A firm, unyielding foundation is one of the most essential features 

 of a brick pavement. This fact can be more readily appreciated 

 when it is considered that the surface of a brick pavement is made up 



