18 BULLETIN" 105, U. S. DEPARTMENT OF AGRICULTURE. 



The road selected for the experiments is commonly known as the 

 Rockville Pike and extends from the District of Columbia line to the 

 corporate limits of Rockville, Md., a distance of approximately 9 

 miles. It was a macadam road originally constructed with quartzite 

 and patched with limestone from time to time. At the time of these 

 experiments it had become rough and badly worn, and was therefore 

 resurfaced before any surface treatments were applied. This work 

 was done on three contracts, the first two of which, including the 

 portion from station + 15 at the District line to station 210, were 

 completed hi July, 1913, and the third, extending from station 210 

 to the corporate limits of Rockville, in October, 1913. The old sur- 

 face was loosened with spikes in the roller wheels and further broken 

 up with a 3-ton scarifier. The surface was then reshaped and rolled, 

 after which from 3 to 3 % inches of new limestone was added and the 

 surface was finished as water-bound macadam. The road was graded 

 25 feet wide in both cuts and fills, and the surface of the finished 

 macadam had a width of 15 feet and a crown of 0.6 inch per foot. 

 The cost of this work averaged 52 cents per square yard or $4,676 per 

 mile of 15-foot road. A section of 10-foot road on Bradley Lane, 1,500 

 feet in length, was also scarified and resurfaced with limestone as water- 

 bound macadam on a separate contract. This was a limestone road 

 which had become badly worn and rutted. The total cost for resur- 

 facing was $1,285.72, or" 75.6 cents per square yard. 



Surface treatment was started on September 5 at the District line 

 on the macadam which had been longest completed. The surface 

 was thoroughly swept with a horse-drawn street sweeper, and any 

 hard cakes of dust were removed with shovels. As the work 

 progressed over macadam which had been more recently completed, 

 these cakes of dust became more numerous, and were removed with 

 considerable difficulty. The advisability of permitting traffic to con- 

 solidate and wear a new macadam surface to a reasonable extent 

 before surface treating was thereby demonstrated. All the bitumi- 

 nous materials were delivered in tank-car lots of from 5,600 to 5,800 

 gallons with an average haul of 1 J miles from the road. The material 

 was heated at first by a small portable boiler, but as colder weather 

 developed it was found necessary to engage a 40-horsepower traction 

 engine in order to heat the heavier materials properly. 



The application was made by means of two 600-gallon distributors 

 which were each drawn by one team. They were equipped with a 

 gasoline pump developing about 40 pounds pressure at the nozzles. 

 The material was ejected from slotted nozzles hi fan-shaped sprays 

 so spaced as to cover half the width of the road on each passage of 

 the machine. 



