Recent years have seen a surge in research related to green construction and solid waste recycling. Soil stabilisation has been a research focus in recent times. It primarily involves treating soil with stabilisers to enhance its mechanical properties, enabling applications in road subgrades, slope reinforcement and other civil engineering projects. Currently, cement is the dominant stabiliser in most engineering practices, yet it poses notable environmental concerns due to high carbon emissions. Solid wastes, such as coal bottom ash (CBA) and ground granulated blast furnace slag (GGBS), can be utilised to produce geopolymers under alkaline activation intended for use as a cement substitute in soil stabilisation. The addition of desulfurization gypsum (DG) is expected to further enhance its strength. However, limited research has been conducted on the mechanical performance and microstructural behaviour of geopolymer-stabilised soil based on the ternary system of coal bottom ash (CBA), ground granulated blast furnace slag (GGBS), and desulphurisation gypsum (DG) under alkaline activation. This thesis focuses on stabilising excavated soil from Ningbo with a high-water content (80% by mass of dry soil). CBA, GGBS, and DG were used as the precursors of the binder, and sodium hydroxide (NaOH) and sodium silicate (Na2SiO3) were employed as the alkaline activators to produce the geopolymer. The unconfined compressive strength (UCS) was evaluated. Results indicate that adding DG can significantly enhance the compressive strength of the stabilised soil; an 8% DG addition doubled the strength. A maximum alkaline activator dosage of 30% was found to optimise the 28-day UCS, achieving a peak value of 6.66 MPa when a 40% precursor content was used in the binder system. Microstructural characterisation via scanning electron microscopy (SEM) and X-ray diffraction (XRD) was performed to elucidate the stabilisation mechanism. The results demonstrated that the formation of N-(C)-A-S-H gel, C-(A)-S-H gel, and ettringite (AFt) contributed to the strength improvement. This study proposes a more environmentally friendly approach for utilising alkali-activated coal bottom ash in stabilising excavated soil for road-fill embankment construction, promoting the sustainable reuse of solid waste.
Utilising alkali-activated coal bottom ash for the stabilisation of excavated soil in road-fill embankment construction
FAN, T. (Author). 15 Jul 2026
Student thesis: MRes Thesis