Towards Net-Zero Ground Improvement: Sustainable Sulfate Soil Stabilisation Using Lime, Ground Granulated Blast Furnace Slag and Metakaolin

Abstract

This article presents laboratory experiments examining the potential benefits of the synergistic effects of ground granulated blast furnace slag (GGBS) and metakaolin (MK) on lime (L) stabilisation of synthetic sulfate-bearing soil. The different soil–binder mixtures considered in this study were prepared by partially replacing lime with GGBS, metakaolin, or a combination of both, at substitution levels ranging from 25% to 75% by mass. The engineering performance of the mixtures was characterised through physico-mechanical analyses (unconfined compressive strength and linear expansion) and microstructural analyses (X-ray diffraction and scanning electron microscopy). Among the binary binders examined in this study, the GGBS-rich binder demonstrated the highest strength, while the metakaolin-rich binder exhibited the lowest swelling behaviour. This difference in performance was balanced by the ternary L–GGBS–MK blend, particularly at a blending ratio of 5L–12.5GGBS–2.5MK. This optimal blend produced a near-zero linear expansion of 0.04%, with only a negligible reduction in strength compared with the binary blend 5L–15GGBS. By replacing a substantial proportion of lime with industrial by-products, the proposed stabilisation strategy reduces reliance on high-carbon conventional binders, supporting the development of green, low-carbon, and resource-efficient construction materials. The findings demonstrate the potential of circular material utilisation to mitigate sulfate-induced heaving while enhancing the durability and sustainability of ground improvement practices. This innovative approach addresses geo-environmental challenges associated with lime stabilisation and aligns with the broader transition towards net-zero construction, promoting the beneficial reuse of industrial by-products, reducing embodied carbon, conserving natural resources, and advancing environmentally responsible geotechnical engineering solutions for sustainable infrastructure development.