Evaluation of Sustainable use of a Residue Sand as a Highway Embankment Material

Abstract

The coarse fractions of the bauxite residue or the residue sand left over from the alumina production process are currently generated in Western Australia. The construction and operation of such large impoundment areas is costly. This has led to research in residue sand recycling. The treatment method used to improve the residue sand in this investigation was pozzolanic stabilisation which is a result of the mixing the residue sand with fly ash and lime. Lime used in this study is the residual lime left over from the Bayer process of Alumina refineries and fly ash is the finest fraction of coal ash produced in coal power stations. This stabilisation technique utilises three industrial by-products for an embankment material thereby providing a sustainable reuse option in alternative to current stockpiling practices.Our findings show that 1) the optimisation program successfully found the optimum mixture of 75% the residue sand, 10% residual lime and 15% fly ash (dry mass). This mixture then allowed for focused and in depth engineering tests to be conducted only upon the optimum residue sand mixture, 2) there was a vast improvement in strength with the addition of fly ash and residual lime to the residue sand and was due to both mechanical and lime stabilisation, and 3) limit equilibrium slope stability analysis of embankments with different geometries was performed to determine suitable slopes that satisfied the strength requirement. The results indicated that for embankment heights less that 15m a slope of 2H:1V or flatter for washed and carbonated residue sand while a slope of 1H:4V or flatter for stabilised residue sand sand meet the stability requirements.