Citation

Paige-Green P. Transp. Res. Rec. 1999; 1652: 10-15.

Copyright

(Copyright © 1999, Transportation Research Board, National Research Council, National Academy of Sciences USA, Publisher SAGE Publishing)

DOI

10.3141/1652-36

PMID

unavailable

Abstract

Nearly all structural layers in roads originate as geological materials. The geological origin and chemical and mineralogical composition of these rocks varies considerably and after natural weathering processes affect the fresh rock, a wide range of potential construction materials evolves. After noting that the performance of geological materials in roads is better predicted by an engineering geological classification than by a strictly geological classification, an engineering geological classification system was developed in southern Africa during the late 1960s. This classified materials on the basis of their weathering potential, and products related to their expected performance in roads and the characteristics of each group are discussed. It is shown from an investigation of the performance of a wide range of materials used in unsealed road wearing courses that the engineering geological classification of a material cannot be used to predict accurately its performance in unsealed roads. Factors including mineralogy, geological structure, stage of weathering, local hydrological conditions, and the prevailing and past climate all have a major influence on their performance. Laboratory-determined geotechnical test results are necessary for acceptable classification purposes. The variability of these materials after weathering, however, increases the risk of their use and makes selection more difficult. Mechanisms for selecting and treating appropriate materials for use in unsealed roads are suggested.

Language: en