Physical characteristics of sands amended with fly ash

Abstract

Fly ash from a coal-fired power station was incorporated with each of a 'fine' (0.2-0.5 mm) and 'coarse' (1.4-2.0 mm) sand fraction to give mixtures containing 0, 10, 20, 30, 40, 50, 75 and 100% fly ash by weight. The addition of 10% by weight of ash increased the available water capacity by factors of 7.2 (1.0-7.2% by weight) and 13.5 (0.4-5.4% by weight) for the 'fine' and 'coarse' sands respectively. Subsequent additional 10% increments of ash increased the capacity by smaller amounts. The saturated hydraulic conductivity of the sands decreased markedly with ash addition. The changes in available water capacity and hydraulic conductivity were associated with an increase in capillary pores at the expense of non-capillary pores. Addition of fly ash to both sand fractions resulted in a bilinear relationship between void ratio (volume voids/volume solids) and fly ash percentage in the mixes which was closely related to that theoretically predicted for binary mixtures. The measured void ratios of the mixes exhibited minimum values at 36% and 20% ash by volume for the 'fine' and 'coarse' sand mixes respectively, which compared with the theoretical void ratios for these mixes of 27% and 23% respectively.