EOAD MODELS. 17 



ROCK-ASPHALT MACADAM ROADS. 



Plate VIII, figure 2, represents a rock-asphalt macadam road sur- 

 faced to a width of 16 feet. The macadam is compacted to a total 

 depth of 8J inches and the crown is made one-half inch to the foot. 

 The rock asphalt is spread on the road at the rate of 80 pounds to 

 the square yard. 



Section A represents the prepared subgrade; section B, the first 

 course of stone, ranging in size from 2 to 3 inches, with a depth of 3 

 inches when compacted; section C, the second course of stone, 

 ranging in size from 2 to 3 inches, filled with stone chips or sand, and 

 having a depth of 3 inches when compacted; section D, the third 

 course of stone, ranging in size from \\ to 2\ inches, with a depth of 

 2\ inches when compacted; section E, the rock asphalt, to the extent 

 of 40 pounds per square yard, or about three-fourths inch loose, 

 raked and rolled in to fill the voids ; and section F shows the finished 

 surface, composed of rock asphalt, spread at the rate of 40 pounds per 

 square yard, which is equivalent to a course about three-fourths inch 

 thick before rolling. 



CEMENT CONCRETE ROADS. 



Concrete roads are a comparatively new development in the effort 

 to find a material which will successfully withstand both automobile 

 and horse-drawn traffic. Concrete pavements were laid first in 1869 

 in Grenoble, France, where many streets are still paved with this 

 material. In this country the first use of the concrete pavement was 

 probably in Bellefontaine, Ohio, where several sections were laid in 

 1893 and 1894. 



A large mileage of concrete roads has been built in Wayne County, 

 Mich. These roads are built of a 1:1^:3 mixture throughout, with a 

 minimum thickness of 7 inches. The width of the surfaced roadway 

 varies from 9 to 24 feet. The county road officials are very well 

 pleased with this form of construction, and are building many more 

 miles of it. 



In other instances a leaner concrete is used, and the surface pro- 

 tected by a cushion coat of some bituminous binder with sand, fine 

 gravel, or screenings. This surface coating is renewed as often as 

 may be necessary. 



Plate X, figure 1, illustrates the construction of a concrete road 

 graded to a width of 33 feet and paved to a width of 16 feet. The 

 concrete is placed to a depth of 7 inches in the center and 4 inches at 

 the sides. The crown of the road is three-eighths inch to the foot. 

 Section A represents the prepared subgrade; section B the fresh con- 

 crete placed in position, mixed in the proportion of 1:1|:3; section 

 C, a 2-inch earth blanket, placed to minimize evaporation while cur- 



