DUST PREVENTION AND ROAD PRESERVATION, 1016. 33 
the construction work south of Hume Spring was done after the sur- 
face of experiment 1 was laid. On account of the dripping of the bitu- 
men from the mix as it was hauled over the section, a blotchy, irregular 
seal coat characterized this experiment. This blotchy effect was 
practically all worked out of the surface by careful maintenance, 
although it still was full of slight, short irregularities. On the whole, 
the experiment was in better condition than during the spring and 
early summer of 1916. 
Experiment No. 11 — Bituminous gravel concrete, pit-run gravel with 
refined tar. — This experiment had a browner, more open appear- 
ance than any other gravel section. It had to be slightly patched 
in the summer of 1916, but at the time of inspection was intact and 
in good condition, except for slight irregularities due to construction. 
Experiment No. 12 — Bituminous gravel concrete, pit-run gravel with 
oil-asphalt Y. — This experiment, especially the part between the rail- 
road crossing, was much the best of the gravel sections. It had an 
even, regular, somewhat leathery mat, and was practically free from 
irregularities. At the crest of the grade between the railroads a spring 
broke through the road during the early summer and a stone drain 
had to be laid. Except for repairs at this place, the surface required 
very little attention. Only one spot showed bad wear, and that was 
at Hume Station, where the mixed work joins the brick crossing. 
Experiment No. 13 — Bituminous macadam, trap rock with oil-asphalt 
X; Experiment No. 14, bituminous macadam, trap rock with fluxed 
native asphalt A. — These experiments were very open and porous at 
the time of completion, and one or two small patches had to be made 
to prevent raveling. The binder bled up satisfactorily, and at the 
time of inspection the surfaces presented no apparent difference and 
were intact and in good condition. 
Experiment No. 15 — Bituminous concrete, trap rock with fluxed native 
asphalt A; Experiment No. 16, Bituminous concrete, trap rock with oil- 
asphalt X. — Within 4 months after completion these experiments 
began to ravel badly and experiment No. 16 failed over 60 per cent 
of its area. As the failure occurred during the winter months, it was 
impossible to make proper bituminous patches, so repairs were made 
by removing the old surface where disintegrated and filling the holes 
with a good sand-clay gravel and allowing it to compact under 
traffic. These areas were fairly smooth by spring and then were 
treated with a heavy seal of cold water-gas tar or coal-tar patching 
material and covered with f-inch gravel. At the time of inspection 
both sections were in good condition, although slightly rough in some 
places. The largest breaks in the original surface occurred on the 
fill at approximate station 191, and although a sharp turn occurs at 
station 192, the repairs made appear to have been adequate. 
4588°— 18— Bull. 586 5 
