The effectiveness of waste ash in stabilizing different host materials

In soil stabilization using waste ash, most studies focus on optimizing binder/activator content in a single soil type. The interaction between binders and different host materials remains underexplored. This study investigates the effectiveness of lime-activated waste ash in stabilizing different host materials: well-graded sand, completely decomposed granite (CDG), and marine deposits (MD) by conducting unconfined compression tests. The ash binder, composed of varying proportions of ground granulated blast furnace slag (GGBS) and sewage sludge ash (SSA), was compared with cement. Results show that waste ash is more effective in stabilizing CDG and MD with high water-to-binder (W/B) ratios, while cement works better for sand with low W/B ratios. Scanning electron microscopy and mercury intrusion porosimetry were used to interpret strength differences from the perspective of microstructure. In ash-stabilized CDG and MD, smaller pores promote the formation of dense/interconnected calcium silicate hydrate (C-S-H) networks, resulting in stronger bonding, lower porosity, and higher strength. In ash-stabilized sand, larger pores allow C-S-H to grow in isolated needle/fiber-like forms, resulting in weaker bonding. For cement-stabilized soil, C-S-H morphology varies with the Ca/Si ratio. High W/B ratios result in reduced Ca/Si ratios and longer silicon chains, forming needle/fiber-like C-S-H structures, whereas lower W/B (high Ca/Si) ratios develop dense network-like morphologies with shorter silicon chains. Based on these findings, waste ash is recommended for stabilizing fine-grained soils with high W/B ratios, while cement is more suitable for coarse-grained soils with low W/B ratios. This study highlights that binder effectiveness is closely related to the water content and pore structure of the host material. © 2025 Elsevier Ltd