DUST PEEVENTION AND ROAD PRESERVATION, 1916. 31 
MOUNT VERNON AVENUE, ALEXANDRIA COUNTY, VA., 1915. 
BITUMINOUS MACADAM. BITUMINOUS CONCRETE, BITUMINOUS GRAVEL CONCRETE. 
These experimental sections were constructed on Mount Vernon 
Avenue beginning at the Military Road near Arlington Cemetery and 
extending to Washington Avenue ; thence to Washington Street, to 
the city line of Alexandria. The original report, giving details of 
materials and methods of construction, is published in Bulletin No. 
407, United States Department of Agriculture. In addition, it may 
be stated that experiments Nos. 1 and 2, and 5 to 10, inclusive, bled 
profusely with the first warm weather of the spring of 1916, and re- 
quired the prompt application of torpedo sand to prevent picking up 
under traffic. 
The work was inspected on January 11, 1917, and the condition of 
the experimental sections at that time was as follows : 
Experiment No. 1 — Bituminous macadam, sandstone with fluxed 
native asphalt A; experiment No. 2 — Bituminous macadam, sandstone 
with oil-asphalt X. — There was no marked difference in the appear- 
ance of these experiments. They were in excellent condition, with 
the seal coat still almost intact, particularly on experiment No. 1, the 
bitumen having bled up to form a close, generally uniform surface. 
Experiment No. 2 appeared to have more of the coarse stone exposed. 
Only two or three patches have been made since construction. 
Experiment No. 3 — Bituminous concrete, sandstone with fluxed native 
asphalt A; experiment No. 4 — Bituminous concrete, sandstone with oil- 
asphalt X. — In January, 1916, about 6 months after completion, it 
was noticed that large areas in both of these experiments became cov- 
ered with check cracks, generally in two directions — longitudinally 
and at right angles to traffic. From 24 to 48 hours after the appear- 
ance of these cracks the areas would begin to ravel, and, once broken, 
disintegration would follow rapidly. Temporary repairs were pro- 
vided for at once and only a few of the cracked areas actually broke. 
Those which raveled were dug out carefully and filled with penetra- 
tion patches until, in March, it was possible to apply a general seal 
coat to both experiments. A fluid, refined water-gas tar was used 
and the covering material was torpedo sand. The characteristics of 
the bituminous material are given in Table 36, and the cost data and 
quantities will be found in Table 38. 
Table 36. — Analysis of refined water-gas tar. 
Specific gravity 25° C/25° C 1. 145 
Specific viscosity, Engler, 50° C. 50 c. c 1 26. 5 
Bitumen soluble in CS 2 (total bitumen) per cent. . 98. 92 
Organic matter insoluble (free carbon) do 1. 05 
Inorganic matter insoluble do 0. 03 
100. 00 
i Average of three samples. 
