PORTLAND CEMENT CONCRETE PAVEMENTS. 17 



fact that concrete pavements are seldom reinforced. Furthermore, 

 reinforced pavements are more difficult to repair than those made of 

 plain concrete, which may be a very serious objection under some 

 circumstances. 



GUTTERS. 



It is frequently desirable to provide concrete pavements with paved 

 gutters in order to prevent the side ditches from eroding. Plate XI, 

 figure 2, shows a typical design for a concrete gutter. This design 

 has been frequently used and has usually proved to be satisfactory. 

 A suitable strike board for forming this gutter is also shown in the 

 figure. 



It is impracticable to construct the pavement and the gutter at 

 the same time, and on account of the convenience of using the pave- 

 ment as a platform for material and for mixing concrete for the 

 gutter the pavement is usually constructed first. When there is no 

 space between the gutter and pavement the joints should always be 

 continued through both. If this is not done, the joints in each are 

 apt to be continued as cracks in the other. 



CURBS. 



Concrete pavements on country roads are not generally provided 

 with curbs, because it is usually desirable to use the shoulders as part 

 of the roadway. Under some circumstances, however, curbs may be 

 employed to advantage. For example, in deep cuts it might be jus- 

 tifiable economy to omit the shoulders and side ditches and provide 

 curbs along the edges of the pavement so that the sides of the pave- 

 ment would serve as gutters. Likewise, on very deep fills curbs are 

 sometimes used to protect slopes from erosion. When this is done 

 it is necessary to provide catch basins at low points in the grade. 



BITUMINOUS WEARING SURFACE. 



Since 1906 a number of experiments have been made in an eff ort to 

 develop some satisfactory method of constructing a bituminous wear- 

 ing surface on concrete pavements. Various kinds of bituminous 

 materials have been used and several methods of applying them 

 have been tried. Some of the surfaces are reported to have given 

 moderately good service under light traffic, but in general they have 

 not been durable where the traffic is at all heavy. The uneven man- 

 ner in which they fail tends to produce excessive wear on portions of 

 the concrete, and renewals should be made promptly as needed. 



The principal advantages claimed for bituminous wearing surfaces 

 on concrete pavements are: 



(1) They make it possible to substitute continuous maintenance for 

 periodic renewals of the pavement. 

 92759°— Bull. 249—15 3 



