DUST PREVENTION AND ROAD PRESERVATION. 15 
adjoining curb. The seal coat on the District of Columbia pavement 
began to bleed badly with the advent of warm weather, and. in July it 
was necessary to make an application of pea gravel to the extent of 
0.01 1 cubic yard per square yard. This is regarded as supplementary 
construction and charged accordingly. A smooth and excellent 
wearing surface has resulted. 
The results of expansion in concrete during hot weather were noted 
at the joint between experiments Nos. 2 and 3, where the roadway 
buckled across its entire width, and to a small extent sheared off some 
of the concrete base of the District of Columbia pavement. The 
defect was repaired by cutting out a narrow strip of concrete. The 
pavement settled to its original grade, and the slot was filled by three 
double courses of vitrified brick, the joints of which were filled with 
hot coal-tar pitch. 
An inspection of the several bituminous surface treatments applied 
to concrete did not seem to indicate any noticeable difference between 
the adaptability of cement concrete and oil-cement concrete to this 
form of treatment. The condition of the various sections at the time 
of inspection was noted as follows: 
A (Refined coal tar): The adhesion was fairly good, but the bitumen had become 
quite hard and had worn off in a number of small spots. 
B (Water-gas. tar preparation No. 2) : The adhesion was about the same as the coal tar, 
but much fewer places had worn through. 
C (Fluxed native asphalt No. 2): The adhesion was not particularly good. There 
were no failures in the east half of the road, but for one-third of the width on the west 
side the treatment was about 30 per cent gone. 
D (Fluxed native asphalt No. 2 over water-gas tar preparation No. 1): There were 
but few failures on the north two-thirds of the section; the bitumen was flexible and 
the adhesion good. There was extensive patching in the south third, but a large part 
of this was due to damage done by a traction engine shortly after the section was 
completed. 
E (Fluxed native asphalt No. 1 over a native asphalt emulsion): The adhesion was 
poor. There were few small failures on the east half of the roadway, and about 40 
per cent of the treatment was gone on the west half. 
F (Oil asphalt No. 1 over water-gas tar preparation No. 1): The adhesion was poor, 
and the treatment was about 50 per cent gone throughout. One very good piece was 
left on the east half at the south end. 
G (Befined coal tar): The condition was about the same as section A. 
H (Water-gas tar preparation No. 2): This section was in very good condition. The 
adhesion was good and there were only two or three very small bare places. 
I (Fluxed native asphalt No. 2) : The north half was good, but there were a few large 
bare places in the south half on the east side of the road. 
J (Oil asphalt No. 2): This section was generally good on the east half of the road, 
with several fairly large bare places along the west side. 
In connection with the above report, it should be said that prac- 
tically all of the sections suffered to a greater or less extent from the 
passage of a traction engine over them. This occurred during a 
rather warm spell shortly after the completion of the work, when the 
