DUST PREVENTION" AND ROAD PRESERVATION, 1915. 43 



Experiment No. 2. — Sand-Oil Asphalt. 



Location: Station 212+92 to station 220+85. 



Length: 793 feet. 



Area: 1,233.56 square yards. 



Details. — The subgrade on the east end of this experiment, from 

 station 212 + 92 to station 217 + 30, was an old sand-clay road, and 

 in general provided a firm foundation. On this section the subgrade 

 was dressed and rolled and the sand-asphalt mixture laid 2| inches 

 thick after compression. The subgrade from station 217 + 30 to 

 station 220 + 85 consisted of fine sand, and the wearing course in this 

 section is 3| inches thick, laid in one course from station 217 + 30 to 

 station 219 + 00, and in two courses, each roughly If inches thick 

 from station 219 + 00 to station 220 + 85. Difficulty in securing a 

 satisfactory bond between the two courses was experienced, owing 

 to the fine sand distributed over the surface by laborers who walked 

 over the first course. The sand subgrade was rolled with the 6-ton 

 tandem roller, but as this left it much rougher than desired it was 

 smoothed with hand rollers immediately in advance of spreading 

 the mixture. 



The heating and mixing operations were carried on about two-fifths 

 of a mile from the road, where a clean, weU-graded sand was found in. 

 abundance. All the sand was screened to remove twigs and roots, 

 and also to reduce it to a finely divided condition, which undoubtedly 

 faciUtated heating. It was piled over 15-uich corrugated culvert 

 pipes for heating, and stirred occasionally. This method of heating 

 was found to be costly and relatively inefficient, and lack of heated 

 sand limited the daUy output of the mixer to much less than haK of 

 its normal capacity. The mixer, which was provided with revolving 

 blades, was operated by a 4-horsepower gasoline motor, and was 

 placed on an elevated platform, so that it could be emptied directly 

 into a chute above the wagons. For each batch 6 cubic feet of heated 

 sand was carried from the heating pipes to the charging platform in 

 wheelbarrows, each carrymg 2 cubic feet. After stirring the sand 

 to avoid local overheating, oil-asphalt represented by the analysis 

 given in Table 44 was added in an amount equal to about 10 per cent 

 of the total weight, and the mixing was continued until aU particles 

 were thoroughly and uniformly coated with bitumen. The hot 

 mixture was hauled to the road and, from dumping boards laid on 

 the shoulder, was spread with shovels and hot rakes to the required 

 thickness. The forms consisted of timbers placed along each side 

 of the road at the proper grade. As soon as spread, the mix was 

 rolled longitudinally and transversely with hand rollers, and after 

 standing for some tioae, was covered with a light appHcation of 

 Portland cement, and roUcd with the 6-ton tandem roller. The 



