VITRIFIED BEICK PAVEMENTS FOK COUNTRY ROADS. 13 



ordinary circumstances a satisfactory base may be constructed of 

 concrete composed of 1 part of Portland cement, 3 parts of sand, and 

 from 5 to 7 parts of broken stone or screened gravel. 



The sand should be clean and well graded in size, and the stone or 

 gravel should conform to the usual requirements for coarse aggregate 

 to be used in concrete construction. 



Foundations for brick pavements have also been constructed of 

 planks laid on sand, and in some instances of sand alone. These 

 foundations have seldom proved satisfactory for any great length 

 of time, and can, therefore, be economically used only when the 

 pavement is to be constructed of an inferior grade of brick. 



SAND CUSHION. 



Since it is practically impossible to construct an absolutely smooth 

 base, and since there is always a slight variation in the size of pav- 

 ing brick, owing to slight differences in the amount of shrinkage at 

 the time of burning, it is necessary to provide an adjustable cushion 

 of some kind between the base and the brick for correcting these 

 slight irregularities, in order to secure an even surface and a uniform 

 bearing for the brick. Sand has been found a most satisfactory 

 material of which to construct this cushion, and is almost exclusively 

 used for this purpose. The proper thickness for the sand cushion will 

 of course depend on the extent of the inequalities above mentioned. 

 Two inches is the most usual thickness, and has generally proved 

 very satisfactory. One and one-half inches, however, is in many 

 cases entirely sufficient. 



The sand used in the cushion should be moderately clean and free 

 from pebbles. If dirt or vegetable matter is present, it will soon be 

 leached out and cause unevenness to develop in the pavement, while 

 pebbles prevent the brick from securing a uniform bearing and ulti- 

 mately produce the same result. It is also important that the sand 

 should be dry when spread, especially if it is fine, because a compara- 

 tively small amount of moisture increases the volume of fine sand con- 

 siderably, and moisture when present is not, as a rule, uniformly 

 distributed. Even if it were uniformly distributed at the start, some 

 spots would dry out more rapidly than others while the spreading 

 was under way, and a lack of uniformity would thus be produced in 

 the cushion. 



In forming the cushion the sand is uniformly spread over the base 

 to a depth slightly in excess of that desired, and is then smoothed off 

 by drawing over it a template shaped to conform with the cross sec- 

 tion of the finished pavement. The length of the template is ordi- 

 narily made equal to the width of the pavement where this is less than 

 about 25 feet, and equal to half the width for wider pavements. 

 Timber guides may be laid in the same direction as the pavement for 



