Performance of Soil-Based Controlled Low-Strength Material Prepared with Alkali-Activated Slag and Coal Bottom Ash

The utilisation of excavated soil with high moisture and high viscosity faces challenges such as complex dehydration processes and difficult material dispersion. Controlled Low-Strength Material (CLSM) provides a feasible pathway for its dehydration-free resource utilisation. To enhance sustainability, alkali-activated materials can replace Portland cement as the binder in CLSM. However, the influences of activator concentration on CLSM performance remain unclear, and the dispersibility of high-viscosity soil needs further improvement. Therefore, this study develops a novel CLSM using high-viscosity excavated soil and alkali-activated slag, with coal bottom ash (CBA) introduced to improve its dispersibility. Through flowability, setting time, and compressive strength tests, the influences of binder content, alkaline dosage, silicate modulus, soil-to-aggregate ratio, and wet-dry cycles on CLSM performance are systematically investigated, followed by hydration heat and thermogravimetric analyses to reveal the underlying mechanisms. The results demonstrate that increasing the binder content promotes hydration and enhances the mechanical properties of CLSM. CBA can effectively improve flowability but has limited effects on hydration and strength enhancement. Increasing the alkaline dosage accelerates early hydration and increases 7-day compressive strength but may retard later-stage strength development. Reducing the silicate modulus is beneficial to early hydration and performance, whereas a high modulus presents higher later-stage compressive strength. Wet-dry cycles exert dual effects on CLSM through promoting hydration and inducing internal crack propagation, ultimately resulting in strength degradation under wet-dry cycles. This paper provides a theoretical basis and technical reference for the efficient and low-carbon resource utilisation of high-viscosity excavated soil as filling material.