26 BULLETIN 257, U. S. DEPARTMENT OF AGRICULTURE. 



Experiment No. 1 (Bituminous Concrete — Topeka Specification). 



This experiment presents a hard firm surface, with some slight 

 indication of waviness. The latter condition is most pronounced in 

 the trap-rock section adjacent to the curb. The wear in this pave- 

 ment is most evident where the surface is slightly below the top of 

 the concrete curb, and in one place this has been broken and a slight 

 depression has developed. The trap-rock section has a slightly- 

 darker color than that in which limestone was used, and the line 

 between the two is easily discernible. Two lateral cracks were 

 noted in the limestone section about 20 and 40 feet, respectively, 

 south of its juncture with the trap-rock section. These cracks 

 extend from the west curb about half way across the road. A 

 small cup-hole was noted in the middle of the road about 60 feet 

 north of Bradley Lane. 



Experiment No. 2 (Bituminous Concrete — District of Columbia Specification). 



This experiment presents a smooth uniform surface on which the 

 seal coat still remains practically intact. Two lateral cracks, both 

 beginning at the east curb, were noted near the middle of the section 

 in which trap rock was used. One of these extends about one- 

 quarter of the distance across the road and the other about one-half 

 the distance. 



During the early summer of 1914 expansion in the concrete again 

 caused a buckling of the surface at the joint between experiments 

 Nos. 2 and 3. The stress developed was sufficient to force out the 

 bricks which had been used in providing for this condition previously. 

 The bricks were therefore removed, a clean trench was cut out en- 

 tirely across the pavement for a width of about 1 foot and filled with 

 Portland cement concrete. 



Experiment No. 3 (Cement Concrete and Oil-Cement Concrete — Surfaces 

 Treated with Bituminous Materials). 



The several sections of this experiment have been permitted to 

 wear without repairs, and the condition of the various sections at the 

 time of this inspection was noted as follows: 



(A) Refined coal tar. — The surface treatment has worn off in fairly 

 large areas throughout the entire section. 



(B) Water-gas tar preparation No. 2. — The surface has worn off in 

 small areas throughout the entire section, in most cases not exceeding 

 1 square foot. This section is in an appreciably better condition 

 than No. 1 through its retention of more of the original treatment. 



(C) Fluxed native asphalt No. 2. — The bitumen in this section is 

 still quite pliable, but the surface treatment has largely worn off over 



