14 BULLETIN 373, U. S. DEPARTMENT OF AGRICULTURE. 
which can not afford proper construction in the beginning should 
select such an expensive type of surface for their roads. 
(■i) The material composing the foundation should be of a uniform 
character and free from vegetable matter of any kind. After the 
curbs are set, the foundation should be rerolled and reshaped until it 
is firm and unyielding and conforms to the required grade and cross- 
section. In order to accomplish this final shaping, the sand must be 
kept moist, and it is usually necessary to provide a pipe line along 
the work to supply water for sprinkling the foundation. 
Plate II, figure 1, shows how a brick road on a sand foundation 
has settled under the action of traffic. This settling would probably 
not have occurred if the above precautions had all been observed at the 
time of construction, though the fact that sand, instead of Portland 
cement grout, was used for filling the joints was no doubt a con- 
tributing weakness. 
BEDDING. 
Since it is practically impossible to construct an absolutely smooth 
base, and since there is always a slight variation in the size of paving 
brick, owing to differences in the amount of shrinkage at the time of 
burning, it is necessary to provide an adjustable bedding of some 
kind between the base and the brick in order to secure au even sur- 
face and a uniform bearing for the brick. Until recently sand has 
been almost exclusively used for this purpose and has in general 
proved satisfactory. The objections which have been advanced 
against the sand bedding are, first, that it may become saturated 
with water, which upon freezing might damage the pavement; 
second, that a gradual movement of the sand may occur under the 
jarring action of traffic and in this way the surface of the pavement 
may eventually become distorted; and, third, that the use of some 
material for the bedding which would bond the brick to the base 
would enable the pavement to distribute concentrated loads over a 
greater area of the subgrade than where a sand cushion is used. It 
has also been claimed that the sand bedding, by separating the brick 
from the base, is responsible for much of the noise produced by 
traffic over brick pavements. In order to overcome these objections 
some engineers are now providing that the bedding shall be con- 
structed of a dry mixture of sand and Portland cement instead of 
sand alone. This mixture, which is called " dry mortar," becomes 
wet when the brick are sprinkled just prior to grouting, and upon 
hardening forms a partial bond between the base and the brick. 
When such a bond is formed the bedding is not disturbed by the 
jarring action of traffic and is also partially impervious to water. 
The dry mortar bedding is at present employed only where the base 
is made of concrete, and its use has by no means become general, 
even with the concrete base. 
