DUST PREVENTION AND EOAD 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. 



Gr (Refined 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 



