Coal-biomass fly ash as cement replacement in loess stabilisation for road materials

This study investigated the effect of coal-biomass fly ash (CBFA) as a cement replacement to stabilise the problematic loess for base and subbase applications. The strength and compressibility characteristics of cement and CBFA-stabilised loess were examined by unconfined compression and oedometer tests under different mix proportions and curing times. The unconfined compressive strength (UCS) tended to increase to the optimum value at the CBFA replacement of cement equal to 10% and then decreased with the increase of the CBFA replacement. The soaked UCS of loess stabilised with 3 and 5% cement, and the 40% CBFA replacement met the strength requirement of the subbase and base courses, respectively. The compression of the stabilised loess reduced with the increase in the CBFA replacement by up to 10%, then the compression index tended to increase. The UCS and modified soil-moisture/cement ratio were found as a unique relationship independent of content, cement content, CBFA replacement and moulding moisture. Furthermore, the void ratio of stabilised loess was normalised using a novel parameter known as the equivalent saturated void ratio (esat). The observed relationships are useful for estimating the design parameters of cement and CBFA-stabilised loess for road materials.