DUST PREVENTION AND ROAD PRESERVATION, 1915. 9 
DESCRIPTION OF EXPERIMENTS. 
Experiment No. 1. — Bituminous Macadam (Penetration Method); Sandstone 
with Fluxed Native Asphalt A. 
Location: Station —(1+61) to station 5+00. 
Total length: 661 feet. 
Total area: 1,202.2 square yards. 1 
The compacted gravel base described above had been under traffic 
for 5 months before the experimental surface was begun. The base 
was generally smooth and hard, but a few depressions had developed ; 
these were filled and the surface was cleaned and rolled. Three 
inches of lj-inch crushed sandstone was then spread by shovels from 
piles along the road. The stone had the physical properties shown 
in Table 4 and the mechanical analysis shown in Table 5. Uniform 
spreading was accomplished by the use of 3-inch cubical blocks 
and all irregularities were subsequently brought to a true surface. 
A 10-ton macadam roller was used to compact this stone layer, except 
that whenever available an 8-ton tandem roller was used to advantage 
for this purpose. The bituminous material was a fluxed native asphalt 
of properties shown in Table 8. It was heated in 500-gallon kettles 
mounted on trucks. When the asphalt had reached a temperature 
of 300° to 350° F. it was drawn off into 3J-gallon hand-pouring pots 
and a uniform penetration coat of approximately 1.5 gallons to the 
square yard applied. While the oil was still hot clean stone chips 
were uniformly spread to fill the superficial voids and immediately 
rolled. The chips were broomed to an even distribution and excess 
chips removed as the rolling progressed. 
A seal coat of hot asphalt approximately one-half gallon to the 
square yard was then similarily applied. Chips were then applied in 
such quantity as to leave a slight excess, and the surface was again 
rolled. The mechanical analysis of the sandstone chips is shown in 
Table 7. All the sandstone chips broke up immediately under rolling 
and traffic. 
Experiment No. 2. — Bituminous Macadam (Penetration Method); Sandstone 
with Oil-Asphalt X. 
Location: Station 5+00 to station 18+00. 
Total length: 1,300 feet. 
Total area: 2,599.7 square yards. 2 
The construction of this experiment was exactly as described for 
Experiment No. 1, except that the asphaltic material was an oil 
asphalt described in Table 8. A subdrain was constructed on the 
right from station 12 + 50 to station 18 + 25. It was built with 
6-inch bell and spigot joint tile pipe laid 4 feet below the finished 
grade, and was covered to a depth of 12 inches with broken stone, 
1 Includes 27 square yards at end of cut-off. 2 Includes 289 square yards at beginning of cut-off. 
52086°— Bull. 407—16 2 
