28 BULLETIN 105, TJ. S. DEPARTMENT OF AGRICULTURE. 



Experiment No. 6. — Penetration method — Hot, heavy oil. 



Location: From station 11+55 to station 12+62. 

 Length: 107 feet. 



Method. — Owing to the difficulty in securing a surface of uniform 

 texture with unscreened rock, it was decided to lay a section with 

 new, screened material. The rock furnished from the pit was passed 

 over a f-inch screen and the material retained was spread to a loose 

 depth of 3 inches on the regraded road surface. Oil was applied at 

 the rate of about 1 gallon per square yard, and this was sufficient to 

 flush the voids. The penetration was evidently about 2 inches in 

 depth over the entire surface of the section. From station 11+55 

 to station 1 1 + 80 new rock screenings were used as a top dressing, 

 and over the remainder of the section sand was used for this purpose. 



SUMMARY OF EXPERIMENTS AT MIAMI, FLA. 



An inspection of these experiments in December, 1913, showed Nos. 

 1 and 2 to be in very bad condition and demonstrated the impracti- 

 cability of treating the original coralline rock roadway either by 

 attempted penetration or strictly surface application of bitumen. 

 Experiments Nos. 3 and 4 presented a very satisfactory appearance 

 and there was little difference between them. No real failures were 

 evident. Experiment No. 5 was not as satisfactory, although only 

 two or three small holes had developed in it. Experiment No. 6, 

 where new, unscreened rock was used, was in excellent condition and 

 showed no indication of weakness anywhere on its surface. The 

 cross section was true throughout and it had not worn perceptibly, 

 although the untreated road immediately north of it had worn fully 

 an inch during the preceding six months. 



The cost data are based upon the following unit prices for labor 

 and materials: 



Foreman (per 10-hour day) $3. 50 



Rollerman (per 10-hour day) 4. 00 



Pit boss (per 10-hour day) 3. 00 



Labor (per 10-hour day) 1. 50 



Teams (per 10-hour day) 6. 00 



Rock, in pit (per cubic yard) 15 



Screened rock $1. 75 



Sand, on work 1. 06 



Light asphaltic petroleum (per 

 gallon) 162 



Heavy asphaltic petroleum (per 

 gallon) '.. .1S2 



No charge was made for heating kettles, pouring pots, or other 

 necessary equipment. 



