The use of waste materials in fill and capping layers

The report reviews the extent to which waste materials and industrial by-products can be used as substitutes for naturally-occurring aggregates for bulk fill, selected fill and capping layer construction. In this context fill was taken to mean all those materials covered in the Series 600 of the Manual of Contract Documents for Highway Works, Volume 1: Specification for Highway Works (December 1991), (MCHW 1). Road building plays a significant role in the demand for aggregates as it accounts for about one-third of the total consumption. Some 96 million tonnes were used in 1989. The review considers the possible advantages, disadvantages and potential uses of various waste materials available in the UK and identifies some suitable materials: blastfurnace slag, pulverised fuel ash (pfa), colliery spoil, china clay sand, slate waste, spent oil shale, crushed concrete, crushed brick and asphalt planings all have potential uses in fill and capping layers. The report concludes that there are few technical obstacles to the use of waste materials but that there is usually little incentive to use them in preference to naturally-occurring materials.