EOAD MODELS. 17 
ROCK-ASPHALT MACADAM KOADS. 
Plato VIII, figure 2, represents a rock-asphalt macadam road sur- 
faced to a width of 16 I'cot. The macadam is compacted to a total 
depth of 8% 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 1J to 2 J inches, with a depth of 
2 J 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 J: 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 w r ell 
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- 
