THE BITUMINOUS CONCRETE PAVEMENT 123 



the bituminous material is applied hot. The rolling may 

 be done either before or after this application. Some- 

 times if the rolling is done afterwards, the rolls are apt to 

 pick up the surface. If they are wet or oiled this difficulty 

 will be avoided. About 1| gallon of bituminous road 

 material is required for each square yard. This should 

 be applied in dry weather only, preferably when the weather 

 is warm, and it must be applied uniformly. The bitumi- 

 nous materials used are asphalts, heavy asphaltic oils, 

 refined water-gas and coal tars and various combinations 

 of these materials. 



General Remark. The patrol system of maintenance, 

 which in municipal and state work has not been found so 

 successful in America as in Europe, owing to governmental 

 conditions, especially commends itself for parks where a 

 well-organized force is always available. Where the 

 bituminous material exudes to the surface there should 

 be an application of sand or screenings. Disintegrated 

 spots should be removed and filled with a mixed bituminous 

 aggregate, followed by rolling. 



9. Bituminous Concrete. The foundation layer should 

 be 4 to 8 inches in depth of broken stone or telford. At 

 Lincoln Park, Chicago, the bituminous concrete was laid 

 as follows by Mr. Arthur S. Lewis. The bituminous 

 mixture consisted of f-inch limestone, torpedo sand and 

 building sand to which asphaltic cement to the amount 

 of 8 per cent, by weight was added. It was applied in a 

 layer 2| inches deep and rolled with a 10-ton tandem roller 

 by which the bituminous layer was compressed about 

 inch. After the rolling a squeegee coat of pure asphalt 

 was applied, using \ gallon per square yard applied imme- 

 diately after the rolling. On the squeegee coat was spread 

 a thin layer of granite screenings and the rolling was re- 



