DUST PKEVENTTON" AND ROAD PRESEEVATION, 1915. 67 



SUPPLEMENTARY REPORT OF EXPERIMENT MADE AT AMES, IOWA, 



1910. 



OIL-ASPHALT GEAVEL. 



The original report of this experiment was pubhshed in Circular 

 No. 90, and reports of succeeding annual inspections appear, respect- 

 ively, in Circulars Nos. 98 and 99 of the Office of PubHc Roads and in 

 U. S. Department of Agriculture Bulletins Nos. 105 and 257. 



The driveway on which this experiment was made is 27 feet wide 

 between gutters, but owing to local conditions traffic is confined 

 practically to the eastern two-thirds of the pavement. Several 

 shght inequahties appeared in the traveled way in 1914, and these 

 were partly eliminated by reshaping the road with a grader. The 

 surface was then treated with a hght asphaltic oil, but the effect of 

 this treatment had almost, entirely disappeared in December, 1914. 



In June, 1915, a similar treatment of very hght oil was appHed, with 

 no more permanent effect than that of the previous one. 



In October, 1915, a heavier asphaltic oil was apphed to the traveled 

 portion of the road at the rate of one-haM gallon per square yard. 

 This work was done under the direction of the superintendent of the 

 grounds and represents the manitenance the roadway has received 

 since its construction in 1910. When inspected December 10, 1915, 

 the gravel surface was well crowned and was covered with a cushion 

 about three-fourths of an inch thick, shghtly wavy, but dense and 

 well compacted. 



SUPPLEMENTARY REPORT OF EXPERIMENTS MADE AT KNOXVILLE, 



TENN. 



TAR AND OIL PREPARATIONS. 



The original report of these experiments was pubhshed in Circular 

 No. 94, and reports of subsequent annual inspections appear in 

 Circulars Nos. 98 and 99, Office of PubUc Roads, and in U. S. Depart- 

 ment of Agriculture Bulletins Nos. 105 and 257. The last inspection 

 was made December 10, 1915. 



These experiments consisted of three bituminous macadam sections 

 constructed by the penetration method. The binders used were, for 

 section No. 1 a refined coal tar, section No. 2 a refined tar preparation, 

 and section No. 3 an oil-asphalt. By January, 1913, section No. 1 

 had raveled throughout its entire area and by November, 1914, had 

 failed completely except for two small areas. Section No. 2 showed 

 only a small number of raveled places in January, 1913, but by 

 November, 1914, had become so seriously pitted that reconstruction 

 seemed necessary. Both sections impeded motor traffic noticeably. 

 Section No. 3, on the other hand, was still in excellent condition. 



In the spring of 1915 the county road officials ordered the holes in 

 sections Nos. 1 and 2 filled with ciiishod stone. After this rock had 



