Utilisation of Class-F fly ash in xanthan gum–amended neutral or acidic soils

Xanthan gum (XG) is an eco-friendly biopolymer with potential applications in soil amendment. However, in acidic soil environments, the pyruvate groups and glycosidic bonds in XG molecules tend to hydrolyse, thereby weakening the efficacy of soil improvement. In this study, the feasibility of utilising alkaline Class-F fly ash (FA) to assist XG in reinforcing acidic soils was evaluated through proctor compaction, unconfined compression, and one-dimensional consolidation. With the increasing soil acidities, the beneficial effect of FA on the geotechnical performances of XG-amended soils grew. The improvement in both mechanical strength and compressibility of XG-amended acidic soils might be caused by the crossing-linking of XG molecular strands and the mitigated hydrolysis of XG hydrogels due to the presence of FA. Based on the findings, it is suggested to use FA in combination with XG for treating the acidic soils and use XG alone for treating the neutral soils. The research outcomes will promote the reuse of solid waste Class-F FA in sustainable geotechnical engineering practices, for example, biopolymer-based soil amendment in acidic soils.