DUST PREVENTION AND ROAD PRESERVATION, 1916. 15 
Experiment No. 5. — Bituminous Gravel Macadam, Refined Water-gas Tar. 
Experiment No. G. — Bituminous Gravel Macadam, Oil-Asphalt. 
There is practically no difference between the two sections at this 
time, nor is there any evidence of the point where the use of grout 
was discontinued after a short section had been laid. The surfaces 
are in excellent condition and show the aggregate throughout, but 
there is no raveling or displacement. 
Experiment No. 7. — Gravel, Surface Treated with Residual Asphaltic 
Petroleum. 
This experiment had a double application. It is rather badly 
waved from the edges to the quarter points and shows a tendency to 
form broad, shallow depressions in the wheel tracks. The mat, 
however, is practically intact and uniform, and except for the wavi- 
ness along the sides, may be considered in satisfactory condition. 
Experiment No. 8. — Gravel, Surface Treated with Residual Asphaltic 
Petroleum. 
This experiment had only one application. It has a few waves, 
and inequalities of application have left long lean streaks in the 
surface. At one point slight raveling has started along one of these 
streaks and the mat is irregular, and, where lean, shows a marked 
tendency to crumble. 
Such expenses as have been incurred for the maintenance of this 
road will be carried forward and reported in the next progress report. 
EXPERIMENTS ON THE ALEXANDRIA-ACCOTINK ROAD, FAIRFAX 
COUNTY, VA. 
BITUMINOUS GRAVEL CONCRETE AND EARTH OIL-ASPHALT. 
This experimental project is located on the Alexandria- Accotink 
Road, in Fairfax County, Va. It begins at the south end of Hunting 
Creek Bridge, the corporate limits of the city of Alexandria, and 
runs in a southerly direction to Gum Spring. The road was im- 
proved originally during 1914-15 under the post-road act of August, 
1912. It was surfaced to a width of 14 feet with gravel, the com- 
pacted depth of which was 7 inches. The maximum grade was 7 
per cent. 
The old gravel road was reshaped, given a crown of one-fourth 
inch to 1 foot, and covered with an experimental surfacing. The 
total length of the road was 25,100 feet. The width surfaced was 
14 feet, except at some sharp curves and road intersections, where it 
was widened. Gravel shoulders were constructed on either side of 
the finished surface. These were made 4 feet wide in fills and 3 
feet in cuts. The thickness of gravel at the edge of the surface was 
4 inches. 
