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BULLETIN" 373, U. S. DEPAETMENT OF AGEICULTUEE. 



the case of first-class macadam roads. The stone should be durable, 

 and should be graded in size between certain reasonable, fixed limits. 

 It should be uniforml}^ spread on the road, either from dumping 

 boards by means of shovels or from wagons especially designed to 

 spread the material as it is being dumped, "^^liere whole loads are 

 dumped in one place and then spread out to the required depth, it is 

 very difficult to obtain uniform density. Usually those spots where 

 the loads are dumped are more densely compacted than the rest of 

 the base, and this lack of uniformity very soon manifests itself by 

 producing unevenness in the surface of the pavement. The broken 

 stone should be compacted in the usual manner by rolling with a 



OPRRE 12001 



Fig. 3. — Making provision for expansion cushion. 



power roller weighing not less than about 10 tons, and sufficient 

 stone screenings and coarse sand to fill the voids should be spread 

 and flushed into the base while the rolling is in progress. When 

 complete the base should present a surface uniform in grade and 

 cross section and parallel to the proposed surface of the finished 

 pavement. 



Concrete bases are unquestionably better adapted for brick pave- 

 ments than any other type. They are practically monolithic in form, 

 nearly impervious to water, and possess a relatively high crushing 

 strength. All of these qualities may be obtained with a relatively 

 " lean " concrete if the subgrade has been properly prepared. Under 

 ordinary circumstances a satisfactory base may be constructed of 



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