Improved use of pulverised fuel ash as general fill

In the UK, the introduction of a tax on landfill and the tightening of planning consents for disposal provided powerful incentives for the use of industrial by-products such as pulverised fuel ash (PFA) in construction. PFA (known as fly ash in some parts of the world) has a long history of successful use as general fill, including applications in environmentally sensitive locations. However, the current commonly used Specification for Highway Works treats PFA as a manufactured material, and applies an end-product specification for compaction. This form of specification is restrictive as it requires that the maximum dry density and optimum moisture content be determined for each consignment of PFA delivered to site, a process that can take up to two days. In addition, the Specification requires testing to determine effective shear strength parameters under fully saturated conditions for embankment design. No guidance is given on whether peak or post-peak parameters are to be selected for design purposes o...