DUST PREVENTION AND ROAD PRESERVATION, 1916. 49 
ROCKVILLE PIKE, MONTGOMERY COUNTY, MD., 1913. 
SURFACE TREATMENTS ON WATER-BOUND MACADAM. 
The original report of these experiments was given in Bulletin No. 
105, U. S. Department of Agriculture, and reports of inspections 
appear in Bulletins Nos. 257 and 407. The following report describes 
the condition of experiments on February 21, 1917. 
Experiment No. 1 — Refined coal tar, hot application. — This experi- 
ment continued to give trouble. Although the entire section was 
retreated in July, 1915, it became necessary to re-treat that part of 
the section, which was added in July, 1915, as described in Bulletin 
No. 407. Disintegration of the surface on this northern portion of 
the experiment had become so rapid that ordinary repairs were not 
adequate, and on October 18 to 21, 1916, the same bituminous mate- 
rial was used as in the original treatment of Experiment No. 1, an 
application of 0.33 gallon per square yard being made. On account 
of the lateness of the season and the possibility of low temperature, it 
was decided to broom the material in order to assure thorough contact 
with the old surface. The tar was delivered directly from the stills 
in tank wagons equipped with fire boxes and the material was dis- 
tributed by gravity through a flat nozzle and thoroughly broomed. 
The material was applied uniformly and carefully in an effort to get 
the best possible results. The characteristics of a typical sample 
of the bituminous material are given in Table 51 and the cost data 
and quantities will be found in Table 53. 
At the time of the inspection the entire experiment was in bad 
condition. South of Bradley Lane (the original experiment No. 1) 
the road was badly worn and had areas with large numbers of cup 
holes. 
Considering the traffic on this section, the road is too narrow and 
the edges suffered severely on account of the frequent turning out of 
vehicles. North of Bradley Lane, which was re-treated as above 
described, the conditions were but little better. The road showed 
the same weaknesses and was requiring more bituminous patching 
than could be done in the season. It appeared probable that the 
entire section would require very heavy repairs and a general re-treat- 
ment as early in the spring as possible. 
Experiment No. 2 — Refined water-gas tar, cold application. — -As 
contemplated in the last report, it became necessary to re-treat this 
section in July, 1916. Characteristics of a typical sample of the bi- 
tuminous material used are given in Table 51, and the cost data and 
quantities in Table 53. The general condition of this experiment at 
the time of inspection was excellent, and generally the mat was hard, 
unbroken, and uniform. 
