The objectives of this study are disposed toward the development of Kentucky Rock Asphalt for use as a traffic-bound base and surface on rural roads near its source and toward re-development of the material for use as hot-mixed, hot-laid, skid-resistant surface course for higher echelon roads. The material is a natural asphaltic-sandstone which occurs in considerable abundance in Edmonson County and in other outcrops of Pottsville sandstones bordering the eastern rim of the Western Kentucky Coal Fields. From 1900 until the 1950's, rock-asphalt was used extensively in Kentucky and elsewhere for road surfacing and was regarded widely as a premium-grade material -- providing a soft-riding, sand-textured, skid-resistant pavement. The crushed, natural product -- traditionally containing 7.2 percent natural bitumen -- was characteristically tender for a long time after it was spread on the road; consequently, it could not reliably withstand modern traffic. In the past, several attempts were made to process and pre-roast the material to overcome this deficiency, but none proved to be wholly desirable. Production was discontinued in 1956. Re-development began in 1962 with trial uses of lower grade (lean) materials as traffic-bound bases and surfaces on minor roads. These early experiments did not produce favorable performance; in some of the interim experiments, the material was up-graded with additions of liquid and emulsified asphalts; and, in other the raw base courses were sealed, a major development, recently, was the successful production of a hot-mixed, enriched, mixture processed through a conventional dryer, pugmill, etc. The raw aggregate consisted of crushed, graded lean rock -- containing 4 percent or more indigenous bitumen.

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Report Number

No. 233

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