58 BULLETIN 407^ XJ. S. DEPARTMENT OF AGRICULTURE. 



Experiment No. 2. — Bituminous Concrete, District of Columbia Specification. 



This surface continues in essentially the same condition as when 

 last reported. The same cracks were noted and in addition the sur- 

 face is worn near the curb and gutter, but is generally firm and smooth 

 even in these places. Small pits are to be found quite generally 

 scattered over the south two-thirds of the limestone section. These 

 decrease toward the north end. The expansion joint which was noted 

 in the last report as having failed again buckled in the spring and 

 early summer of 1915. The Portland cement concrete block, 1 foot 

 wide and approximately 18 inches deep, which was put in at this joint 

 was sheared horizontally by the stresses developed and the top 6 

 inches of the slab was lifted intact from the rest of the block. To 

 repair this joint, all of the broken concrete of experiment No. 3 was 

 removed. The crack limiting the area of failure was from 2 to 4 feet 

 back of the expansion joint. This entire section was re-laid with 

 concrete similar to the original experiment, with a 2J-uich joint left 

 for expansion. This joint was filled with heavy oil puddled with 

 sand. 



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

 Treated with Bituminous Materials. 



The surfaces of this experiment have been permitted to wear with- 

 out repairs and the condition of the various sections at the time of 

 inspection was noted as follows: 



(A) Refined coal tar. — Twenty to 25 per cent of the surface treat- 

 ment has worn off this section. The side toward the gutter shows 

 considerably more exposed concrete than the other side. 



(B) Water-gas tar preparation No. 2. — This area continues shghtly 

 better than A, but is deteriorating more rapidly now than during last 

 year. 



(C) Fluxed native asplmlt No. 2. — Eighty-five per cent of the mat 

 is gone on the west half and about 1 per cent on the east half. 



(D) Fluxed native asplmlt No. 2 over water-gas tar preparation No. 

 1. — About 85 per cent of this treatment has disappeared from the 

 west half and about 5 per cent from the east half. 



(E) Fluxed native asphalt over native asphalt emulsion. — About 85 

 per cent of this area is bare on the west half of the road and about 10 

 per cent on the east half. 



(F) Oil asphalt No. 1 over water-gas tar preparation No. 1 . — ^A few 

 scattered patches only of the surface treatment remained. 



(G) Refined coal tar. — The surface treatment is worn off to a great 

 extent over the entire section. 



(H) Water-gas tar preparation No. 2. — Seventy-five per cent of the 

 surface is worn off from the west half but the east half remains almost 

 intact. 



