Experimental study on the stabilization of marine soft clay as subgrade filler using binary blending of calcium carbide residue and fly ash

This study endeavors to realize the concurrent utilization of marine soft clay (MSC) and industrial waste, specifically calcium carbide residue (CCR) and fly ash (FA), through a series of experimental investigations. The optimal ratio between CCR and FA, as well as the efficacy of the composite agent (CF–1), were examined, and an empirical equation associating the unconfined compressive strength (q_u) of stabilized MSC was developed through unconfined compressive strength (UCS) tests. Microscopic analyses, including X–ray diffraction (XRD), scanning electron microscopy (SEM), and energy–dispersive spectroscopy (EDS), were employed to unveil the intrinsic mechanisms underlying CF–1 stabilized MSC. Subsequently, the suitability of CF–1 solidified MSC as a roadbed filler was ascertained through laboratory tests. Results revealed the optimum CCR:FA ratio for CF–1 to be 4:1, demonstrating superior curing effects compared to individual components such as Portland cement (PC), CCR, and FA, with commendable environmental and economic benefits. The developed empirical equation exhibited effectiveness in predicting the q_u of CF–1 solidified MSC under varying curing dates (T) and dosages (W_g) conditions. Characterization through XRD, SEM, and EDS identified the primary products formed within the stabilized MSC matrix with CF–1 as comprising calcium–silicate–hydrate (C–S–H) gel, calcium–aluminate–hydrate (C–A–H) gel, and a minor amount of calcite. As T and W_g increased, the reduction in pores between soil particles enhanced the structural integrity and macro–strength of the cured MSC. The failure pattern of CF–1–solidified MSC elementary samples depended on the CF–1 dosage and curing duration. The solidification mechanism of CF–1 on MSC involved pozzolanic, ion exchange, and carbonation reactions. CF–1 solidified MSC satisfied all the specified requirements for roadbed filler in the relevant code, demonstrating substantial potential for in–situ solidification projects involving MSC.