686 EXPERIMENT STATION EECORD. 



engineer. An introductory section dealing with tlie generalities of the subject, 

 including a historical review, is followed by a discussion of vehicles and a 

 mathematical analysis of the reciprocal effects of vehicles and roads. A section 

 on location, design, and construction discusses alignment, cross section shape 

 and structure, surface and underdrainage, foundations, surfacing, and costs. A 

 final section deals with maintenance, including cleaning, rolling, dust prevention, 

 and costs. 



Progress reports of experiments in dust prevention and road preservation, 

 1913 (U. S. Dept. Agr. Bui. 105 {1914), pp. 46). — This report covers the com- 

 pletion of experimental work begun in 1912 (E. S. R., 29, p. 590) and gives the 

 details of construction of several new sample roads. 



An inspection of the experimental roads at Chevy Chase, Md., most of which 

 have been previously described, showed the bituminous concretes to be in ex- 

 cellent condition. The section laid under the Topeka specification had a slightly 

 wavy surface as compared with the District of Columbia pavement and had 

 compressed in a few places below the top of the adjoining curb. The seal coat 

 on the District of Columbia pavement began to bleed badly with the advent of 

 warm weather. The results of expansion in concrete during hot weather were 

 noted at the joint between experiments 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. 



An inspection of the several bituminous surface treatments applied to con- 

 crete did not seem to indicate any noticeable difference between the adaptability 

 of cement concrete and oil-cement concrete to this form of treatment. Practi- 

 cally all of the sections with bituminous surfaces suffered to a greater or less 

 extent from the passage of a traction engine. The exposed concrete surface, 

 as a whole, presenting a smooth, uniform texture and there was apparently no 

 difference in wear between the plain cement and oil-cement concrete. The 

 addition of a hydrated lime had no noticeable effect on the concrete. Cracks 

 devloped at a greater average distance where a limestone aggregate was 

 used. 



No difference was noted in the character of the various sections of brick 

 pavement. The grouted surface had practically all worn off, and at a few 

 places throughout the length of the section small transverse cracks had devel- 

 oped where the grout had broken loose from a course of brick. 



On Rockville Pike, Md., experiments were conducted with tars and oils ap- 

 plied on surfaces hot and cold to demonstrate the relative value of several 

 bituminous products and to ascertain the relative economy, from a maintenance 

 standpoint, of cold treatment with the lighter products as compared with hot 

 treatments with some of the heavier products. In these experiments refined 

 coal tar, refined water-gas tar, asphaltic petroleum, residual asphaltic petroleum, 

 and water-gas tar preparations were used. These were applied to surfaces fin- 

 ished as water boinid macadam and covered with trap rock screenings or 

 gravel. An inspection of these experiments showed that trap rock and gravel 

 coverings have given equally good results. The surfaces were, in general, 

 smooth and firm throughout. 



At Miami, Fla., experiments were conducted with oils and coralline rock. 

 The oils were applied to the rock subsurface by the semipenetration surface 

 treatment and the penetration methods, using cold, light oil and hot, heavy 

 oil. An inspection of these experiments showed two of the sections to be in 

 very bad condition and demonstrated the impracticability of treating ,the 

 original coralline rock roadway either by attempted penetration or strictly 

 surface application of bitumen. The other experiments were in fair condition. 



