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BULLETIN 23, U. S. DEPARTMENT OF AGEICULTUEE. 



uniformly spread on the road, either from dumping boards by means 

 of shovels or from wagons especially designed to spread the mate- 

 rial 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 uniform density. Usually those spots where the loads are 

 dumped are more densely compacted than the rest of the foundation, 

 and this lack of uniformity very soon manifests itself by producing 

 unevenness in the surface of the pavement. Broken- stone and gravel 

 foundations should be compacted in the usual manner by rolling 

 with a power roller weighing not less than about 10 tons, and suffi- 

 cient clean, coarse sand to fill the voids should be spread and flushed 



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Fig. 3.— Making provision for expansion joint. 



into the foundation while the rolling is in progress. When complete 

 the foundation should present a surface uniform in grade and cross 

 section and parallel to the proposed surface of the finished pavement. 

 Concrete foundations are unquestionably better adapted for brick 

 pavements 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 foundation may be con- 

 structed 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. 



