Fibre-reinforced sand-coal fly ash-lime-NaCl blends under severe environmental conditions

Abstract

The use of industrial residues instead of virgin materials is a good alternative for a more sustainable approach to disposing of and managing waste. Soil improvement with coal fly ash (CFA) is particularly attractive for geotechnical earthworks. This study investigated the strength, stiffness and durability of Osorio sand-CFA-lime blends with a variety of improvements by assessing the impact of varying the lime content, fibres, sodium chloride (NaCl) and dry unit weight. Moreover, to contribute to a more rational dosing methodology, strength, stiffness and durability results were correlated to the porosity/binder index [η/(Biv)0.28]. Durability was assessed by comparing wet-dry (WD) and freeze-thaw (FT) cycles, and WD cycles were found to present better performance than FT cycles. Ranks were established for the different components of the blends according to the WD and FT results. The addition of NaCl alone was more effective in improving unconfined compression strength (qu) results than fibres alone. While fibres significantly decreased stiffness at very small-strain shear modulus (G0), NaCl increased G0. The application of η/(Biv)0.28 demonstrated that not only can it predict mechanical behaviour, but also the long-term performance of Osorio sand-CFA-lime blends with or without the addition of NaCl and fibres.