Quality control tests and acceptance specifications for concretionary laterite gravel aggregates: Fid-Bau Portal

Quality control tests and acceptance specifications for concretionary laterite gravel aggregates

Akpokodje, Enuvie G. / Hudec, Peter P.

Abstract In most tropical countries, good and poor concretionary laterite gravels are distinguished solely on the basis of the aggregate impact-strength specifications of the British Standards Institute. Acceptance limits of other aggregate properties (e.g., absorption, specific gravity, etc.) require modifications, because of the peculiar structure and mineralogy of laterite gravels. This paper presents the results of a laboratory study undertaken to develop other quality-control tests and their acceptance limits to supplement the aggregate impact-strength test in evaluating the quality of laterite gravel aggregates. Commonly used concretionary laterite gravels from across Nigeria were used for this study. The laboratory tests performed included sorption tests, density, abrasion, slake durability, Iowa pore index, aggregate impact value, wet-dry cycles and chemical composition. The test results were subjected to bivariant correlation and multivariant stepwise regression-statistical analyses. The study revealed that the ratio of silica to oxides of iron and aluminum, which is known to have a dominating influence on the physico-mechanical properties of laterite gravels can be predicted with reasonable accuracy from the specific gravity. Similarly, abrasion resistance, aggregate impact strength (dry and wet) and durability under wetting and drying cycles can be estimated from empirical multiple-regression relations, involving simple tests such as sorption, density and Iowa pore index (pore-size indexes). These simple tests, therefore, constitute additional quality-control tests. Four quality grades — excellent, good, fair and poor — were established on the basis of the impact strength. The limits of acceptability for each of the recommended simple quality-control test were computed from the relevant linear-regression equations. The main advantage of the proposed new quality-control tests and acceptance limits is the quantitative approach and the ability to recognize four quality grades instead of the usual two. This enables a better selection of laterite gravels for various categories of constructions.