OFFICE OF PUBLIC ROADS. 721 



foundation course was 2^ inches of oil-mixed concrete and was put on in seven 

 diflereut sections, which differed principally in the method of mixing and plac- 

 ing the concrete and in the different kinds of cement that were used. 



Section No. 7 was surfaced by making a stiff mixture of 1 part of cement and 

 2 parts of sand, to which was added oil to the amount of 10 per cent by weight 

 of the ceiuent. This mixture was spread I5 inches thick, and the material was 

 immediately covered with broken stone to a depth of 2i inches and rolled with 

 a 5-ton tandem roller. Repeated rolling failed to fill the voids completely, and 

 so a thin grouting mortar of the same composition was poured over the surface 

 and " broomed " in. After this a light coat of stone screenings was added. 

 This section was 05.S feet in length. 



Section No. G was built with concrete composed of a li : 2 : 4 mixture of 

 cement, sand, and broken stone. Oil to the extent of 10 per cent by weight 

 of the cement was mixed with tlie mortar before the stone was added and the 

 mixture was laid to a depth of 2J inches and tamped until the mortar flushed 

 to the surface. This section was 24.3 feet in length. 



Section No. 5, which was 45 feet in length, was spread with concrete prepared 

 in a " bug " mixer. The cement and sand were mixed dry and, after a proper 

 proportion of broken stone, water, and oil had been added, the whole was mixed 

 and dumped on a board, turned twice by hand, and put in place. The propor- 

 tions of this mixture were 1^ : 3 : 4, with oil to the amount of 10 per cent of the 

 weight of the cement. 



The proportions for the concrete on section No. 4 were 12:1:2:4 of cement, 

 sand, screenings, and broken stone, with an addition of oil to the amount of 

 15 per cent by weight of the cement. The concrete was placed and tamped 

 as described before. The length of this section was 37 feet. 



Section No. 3, G8 feet in length, was identical with section No. 4, except that 

 a different oil product was used. 



On section No. 2 the oil was reduced to 10 per cent by weight of the cement. 

 The section was 72.4 feet in length. Otherwise the experiment was identical 

 with section No. 3. 



No oil was used on section No. 1, in order to compare it with the other 

 sections. Its length was 39.4 feet. 



The road was closed to tratiic for seven days after the last section was laid 

 and the entire work was sprinkled with water daily during this period. 



The cost per square yard of this road varied from $1.15-4- to $1.25+. A total 

 of 762.45 square yards was built.' 



New York, N. Y. — During the months of May and June, 1910, this office, in 

 cooperation with the bureau of engineering and construction of the borough of 

 Richmond, New York City, constructed an oil-mixed concrete road on a part of 

 Innis Street at Elm Park Station, St:, ten Island. The oil for this work was 

 donated by two oil companies and the cement was furnished by four manufac- 

 turers through the American Portland Cement Manufacturers' Association. 

 The borough of Richmond, New York City, furnished labor, sand, and stone, 

 while the Office of Public Roads paid the freight on the oil and cement and 

 furnished supervision of the work. Four sections were constructed, each 32 feet 

 ■wide between the gutters. 



The concrete surface was laid upon an old macadam surface, which was first 

 I»repared and brought to the approximate grade. The concrete was spread 

 about 4 inches deep. In mixing the concrete a machine of the old Smith type 

 was used. The sand and cement were first mixed dry and then water was 

 added, so as to form a thin mortar. A Ixicket of oil was added alternately with 

 a barrow of stone, until all the oil required for the batch had been used, when 

 the remainder of the stone was added After thorough mixing the concrete waa 

 dumped on a board, shoveled into bai'rows, and wheeled to the road. Each 

 batch contained 1 barrel of cement, 8 cubic feet of sand, and 16 cubic feet of 

 crushed stone, varying in size from 1^ inches to three-fourths inch, together 

 with the proper amount of oil. 



On the first section of 163 feet the amount of oil used was 15 per cent by 

 weight of the cement. 



The second section, 77 feet in length, was the same as the first, except that a 

 different brand of Portland cement was used. 



Section No. 3, which was 100.5 feet long, was the same as No. 1, excepting 

 that a third brand of Portland cement was used and a cut-back petroleum resi- 



> For additional details, see Office cf Public Roads Circular No. 94. 

 23165°— AGS 1911 16 



