Wadi gravel – a new concrete aggregate in Qatar: Part 1 – investigation, processing and trials

Abstract

In hot desert regions, attention is turning to local sources of aggregate that were previously regarded as ‘too difficult' to exploit. This paper describes an investigation of such a deposit in Qatar. The material, known as Wadi gravel, is a gravelly sand of Tertiary age cemented by gypsum. A field survey found the gravel content to be in the range of 10 to 20%. As-dug samples had excessively high sulfate content, which could not be removed with conventional aggregate operations. However, intensive treatment in a local sand-processing plant using multi-stage crushing, screening and washing reduced the sulfate to acceptable levels. Petrographic analysis was carried out to identify rock types potentially susceptible to Alkali Silica Reaction (ASR). Trial concrete mixes using the processed Wadi gravel were found to produce satisfactory C40 and C60 concrete. Full-scale building trials were constructed to demonstrate the practicality of using the gravel and assess in-service performance. The smooth surface and rounded particles of Wadi gravel improved the concrete workability and strength, and durability-related properties were similar to concrete made with imported gabbro. Strata similar to Wadi gravel occur widely in hot desert regions and could be useful sources of coarse and fine aggregate for concrete.