24 BULLETIN iOl, U. S. DEPARTMENT OF AGEICULTUEE. 

 EXPERIMENTS ON FALLS ROAD, MONTGOMERY COUNTY, MD. 



SURFACE TREATMENT (OILS, TAR PREPARATIONS, REFINED TARS). 



In the summer of 1913 a series of bituminous surface treatments 

 was applied to Rockville Pike in Montgomery County, Md. The 

 original report of these experiments is given in U. S. Department of 

 Agriculture Bulletin No. 105 and a subsequent report of behavior 

 was made in Department Bulletin 257. In order to make it possible 

 to check the data secured from several of these experiments, another 

 series of comparative test sections was constructed on the FaUs 

 Road, leading from Rockville to Potomac, Md. In the FaUs Road 

 series, sections 1, 2, 4, and 5 were treated with bituminous materials 

 similar to those used on Rockville Pike sections 3, 5, 2, and 1, respec- 

 tively. The coal-tar preparation selected for Experiment No. 3 on 

 FaUs Road had not been used in any previous service tests in this 

 vicinity. Conditions surrounding the two experimental roads are 

 much the same, except that traffic is hghter and the proportion of 

 horse-drawn vehicles greater on the FaUs Road. 



The specifications prescribed a uniform appUcation of one-haH 

 gaUon of bituminous material per square yard, but the amount was 

 varied according to the surface condition of the several sections. The 

 road surface was dry when the apphcations were made, and fine 

 gravel was used to cover the bituminous material. The mechanical 

 analysis of the gravel used is given in Table 24. 



The bitumen was transported to the road and spread by means of 

 two 1,200-gaUon automobile distributors equipped with speed and 

 pressure gauges. The length of the nozzle-line was so adjusted that 

 one-haU of the width of the road was sprayed at one time. The 

 nozzles were of the right-line type, from which the bitumen was ap- 

 phed in a fan-shaped spray under a uniform pressure of approximately 



25 pounds. 



The Falls Road was reconstructed in 1913, and surfaced with 

 water-bound macadam 15 feet wide. Early in the summer of 1915, 

 when the experimental test sections were planned, the macadam 

 surface had become thoroughly compacted, and, with a few excep- 

 tions, was smooth, free from ruts or depressions, and in good condi- 

 tion to receive the bituminous material. In August the contractor 

 distributed aU the gravel required for the work with a two-ton motor 

 truck before he began the apphcation of the bituminous materials. 

 The action of this truck was so severe that when the gravel had been 

 distributed, the water bond in sections 1, 2, and part of 3 was com- 

 pletely broken, and several weak places in the foundation in section 

 2 had formed. The latter were repaired, and an effort was made to 

 reestabUsh the water bond. Owing to the protracted drought and 

 the disturbing action of traffic, this work was only partiaUy sue- 



