12 



BULLETIN 246, U. S. DEPARTMENT OF AGRICULTURE. 



the case of first-class macadam roads. The materials used should con- 

 form in all respects to the ordinary requirements for similar mate- 

 rials used in constructing such roads; that is, the stone should be 

 clean, hard, tough, and durable, and should be graded in size between 

 certain reasonable, fixed limits. It should be uniformly 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. Where whole loads are dumped in one place and then 

 spread out to the required depth, it is very difficult to obtain uni- 

 form 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 



Fig. 3. — Making provision for expansion joint. 



surface of the pavement. Broken stone should be compacted 

 in the usual manner by rolling the base with a power roller weighing 

 not less than about 10 tons, and sufficient clean stone chips 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 uni- 

 form 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 



