14 BULLETIX 373^ V. 5. DEPAETMEXT OF AGEICULTUEE. 



wliicli can not afford, proper construction in tlie beginning slioulcl 

 select sucli an expensive type of surface for their roads. 



(4) 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 reroUed and reshaped until it 

 is firm and unyielding and conforms to the recjuired gi'ade 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 vrork to supply water for sprinkling the foundation. 



Plate II. figure 1. shovrs hovr a brick road on a sand foundation 

 has settled under the action of trafiic. 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. 



BEDDIXG. 



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 briclv in order to secure an 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 trafiic 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 pa^'ement to distribute concentrated loads over a 

 greater area of the sub grade 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 groutmg, and upon 

 hardening forms a partial bond between the base and the brick. 

 ~\"\Tien 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. 



