DUST PREVENTION" AND ROAD PRESERVATION^ 1915. 9 



description op 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.' 



The compacted gravel base described above had been under traffic 

 for 5 months before the experunental surface was begun. The base 

 was generally smooth and hard, but a few depressions had developed ; 

 tJiese were filled and the surface was cleaned and rolled. Three 

 inches of 1^-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 accomphshed 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-gaUon kettles 

 mounted on trucks. When the asphalt had reached a temperature 

 of 300° to 350° F. it was drawn off into 3^-gallon hand-pouring pots 

 and a uniform penetration coat of approximately 1.5 gallons to the 

 square yard applied. While the oil was stUl hot clean stone chips 

 were uniformly spread to fill the superficial voids and immediately 

 roUed, 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 simUarily apphed. 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. 



ExPBEiJiENT Xo. 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.^ 



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 beU and spigot joint tile pipe laid 4 feet below the finished 

 grade, and was covered to a depth of 12 inches with broken stone, 



• Includes 27 squaroyarrla at end of cut-off. ^ Includes 289 square yards at beginning of cut-off. 

 52086°— Bull. 407—16 2 



