12 



BULLETIlSr 40*7, U. S, DEPAETMEISTT OF AGEICULTUEE. 



Experiment No. 7. — ^Bituminous Macadam (Mixing Method); Gneiss with 



Oil-Asphalt X. 



Location: Station 58+45 to station 71+78. 



Length: 1,333 feet. 



Total area: 2,369.8 square yards. 



The crushed gneiss used in the bituminous mixture had the phys- 

 ical properties shown in Table 4 and of mechanical analysis shown in 

 Table 6. The mechanical analysis of the gneiss chips used on this 

 experiment is shown in Table 7. The experiment was otherwise 

 exactly similar to experiment No. 4. 



Experiment No. 8. — ^Bituminous Macadam (Mixma Method); Gneiss with 

 Fluxed Native Asphalt A. 



Location: Station 71+78 to station 78+65. 



Total length: 587 feet. 



Total area: 1,221.3 square yards. 



This experiment is exactly similar to experiment No. 7, except 

 that fluxed native asphalt A, with properties as shown in Table 8, 

 was used instead of the oil-asphalt. 



Experiment No. 9. — ^Bituminous Gravel Concrete, Pit-Run Gravel, with 



Oil-Asphalt Y. 



Location: Station 78+65 to station 89+50. 



Total length: 1,095 feet. 



Total area: 2,152.1 square yards. 



Table 10. — Typical analyses of oil-asphalt gravel mixtures used in experiment No. 9. 





I. 



II. 



in. 



Bitumen soluble in CS^ 



Per cent. 

 6.4 



5.7 

 16.9 

 17.1 

 12.6 

 8.5 

 10.3 

 11.0 

 6.5 

 6.2 

 0.8 

 2.2 

 2.2 



Per cent. 

 6.9 



6.7 

 11.4 

 19.9 



12.2 

 6.5 

 10.5 

 11.4 

 8.9 

 6.1 

 0.8 

 2.8 

 2.8 



Per cent. 

 7.5 



Mechanical analysis of aggregate: 



Passing 1-inch screen, retained on |-inch screen 



4.4 



Passing f-inch screen, retained on |-inch screen 



12.8 





18.6 





13.9 



Passing lO-mesh sieve, retained on 20-niesh sieve 



6.5 





8.6 





11.1 





7.2 



Passing SO-mesh sieve, retained on SO-mesh sieve 



6.4 





1.0 





3.4 



Passing 200-raesh sieve 



6.1 







Total 



100.0 



100.0 



100.0 







The gravel base for this experiment had been open to travel several 

 weeks and was hard and smooth when surfacing commenced. Wh.er- 

 ever small depressions or irregularities had developed they were 

 corrected by hand picking and the application of new gravel, which 

 was thoroughly rolled. 



The gravel used for the aggregate in the bituminous concrete was 

 a uniform dense gravel containing much fine material, as shown by 



