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 J 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 3i 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, well-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 
facilitated heating. It was piled over 15-inch 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 daily output of the mixer to much less than half 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 carrying 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 all 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 time, was covered with a fight application of 
Portland cement, and rolled with the 6-ton tandem roller. The 
