VITRIFIED BRICK AS MATERIAL FOR COUNTRY ROADS. 9 
The shoulders, while essentially a part of the road surface, should 
be constructed at the same time that the subgrade is formed. This 
is necessary in order that the curb may be properly supported while 
the pavement is being laid and rolled. The shoulders should never 
be less than 4 feet wide and should consist of some material which 
compacts readily under the roller and which 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 pavement of considerable 
traffic during favorable seasons and thereby adds greatly to its life. 
The general method of constructing shoulders for brick roads is not 
essentially different from that employed for other types of pave- 
ments. 
CURBING. 
All brick pavements should be supplied with 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 will soon spread over the entire pavement. Properly 
constructed curbing, on the other hand, will 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 condi- 
tions 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 structure, 
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 have a 
depth of from 18 to 36 inches, depending on traffic 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 6 
inches and, where the traffic conditions are not severe and the quality 
of the stone is good, a thickness of 4 inches will ordinarily prove 
satisfactory. Stone curb should always be set on a firm bed of 
7709°— 13 2 
