This report describes the results obtained from a field and laboratory study of natural rock asphalts occurring in the intendencia of caqueta, republic of Colombia. The aims of the study were to locate sources of asphalt, to estimate available quantities and, by testing representative samples, to evaluate the suitability of the asphalt for use either as bases or surfacings in a proposed road building project. The natural asphalts, which occur in association with tertiary sandstones and conglomerates, closely resemble in aggregate grading the low stone content asphalts as described in British standard 594: 1973. Samples obtained from a preferred local source were found to contain between 6 and 9 per cent of soluble bitumen in the 100/150 pen range. Examination of existing road surfacings built with material from the same source showed that hardening to 10/20 pen may be expected over a period of 12 years in a wet, tropical environment. A laboratory investigation showed that the Marshall test may be used to select suitable material for road construction and tentative criteria are given. The performance of the asphalt may be improved by mixing material from different sources and by the use of a hot process for mixing and laying. To provide a durable surface under heavy traffic, it may be desirable to surface dress the asphalt.
Abstract