VITRIFIED BRICK AS MATERIAL FOR COUXTRV ROADS. 17 
The first application should proceed about 50 feet in advance of the 
second. Usually both applications are made by the same crew of 
laborers. ■ They simply turn back after having covered the allowable 
distance with the first application and, mixing the grout hi the same 
boxes, bring up the second application: The second application of 
grout should completely fill the joints flush with the top of the brick. 
After the joints are filled as described above and the grout has taken 
its initial set. the entire surface should be covered to a depth of 
approximately one-half inch with clean sand. This is done to protect 
the pavement from the weather and to keep it in a moist condition 
while the grout is hardening. If necessary, in order to keep the sand 
moist, it should be occasionally sprinkled for several days after it is 
spread. 
The sand covering should be permitted to remain on the surface 
for at least 10 days, and during this period the pavement should be 
kept entirely closed to traffic. If the weather is unfavorable, the 
length of time during which traffic is kept off the road should be 
increased. 
EXPANSION CUSHIONS. 
It has been customary in the past to provide both longitudinal and 
transverse bituminous expansion cushions hi grout-fined brick pave- 
ments, but recent practice has demonstrated that the transverse 
cushions may be advantageously omitted if proper longitudinal 
cushions are provided. The principal objection to the use of trans- 
verse expansion cushions is based on the fact that the material com- 
posing the cushions frequently softens during warm weather and 
runs out toward the curb, thus leaving the edges of the adjoining 
brick exposed to destructive impact from the wheels of passing 
vehicles. Even if the cushion consisted of a material which does not 
run hi warm weather, it is necessarily softer than the brick, and the 
natural result is still the development of unevenness hi its immediate 
vicinity. Xo such objection can exist concerning longitudinal 
expansion cushions, however, if they are placed adjacent to the curbs 
and constructed of proper material. They not only furnish a means 
for the pavement to expand and contract with changes hi tempera- 
ture but they also eliminate to a large extent the disagreeable 
rumbling which has been so frequently associated with grout-filled 
brick pavements. 
The bituminous material of which the expansion cushions are made 
should be such as to remain firm hi summer and not to become brittle 
in winter. It should also possess the quality of durability. In order 
to insure that any given material is suited for such a purpose, it is 
usually considered necessary to prescribe certain laboratory require- 
ments to which it must conform, and examples of these, which have 
7709°— 13 3 
