Sustainable stabilisation of collapsible loess with quicklime-recycled GGBS mixtures

Abstract

Loess subgrades are highly susceptible to collapse upon wetting, leading to excessive settlement and threatening pavement safety. Loess stabilisation using cement/lime is commonly adopted in practice, but their production is associated with high energy consumption and carbon emissions. Hence, this study investigates the collapse of loess treated with mixtures of quicklime and recycled ground granulated blast furnace slag (GGBS). Comprehensive one-dimensional compression tests, with wetting applied at 50 and 200 kPa, were conducted on specimens with different degrees of compaction, curing times, binder contents (the mass ratio of quicklime and GGBS to dry soil), and GGBS-to-binder ratios (the proportion of GGBS in the total binder). Results show that the collapse index, when plotted on a logarithmic scale, decreases linearly as binder content increases. Moreover, at a given binder content, increasing the GGBS-to-binder ratio can better mitigate loess collapse. For instance, when the binder content increases from 0% to 3%, the collapse index decreases from 15.3% (severe collapse) to 4.7% (moderate collapse) and 0.06% (nearly non-collapse) when the GGBS-to-binder ratio is 0% and 50%, respectively. Thermogravimetric analysis shows that quicklime treatment primarily increases Ca(OH)₂ and CaCO₃ contents, and partial substitution with GGBS promotes the formation of additional calcium (aluminate) silicate hydrate (C-(A)-S-H) phases. These products reduce wetting-induced collapse by coating soil particles, filling interparticle voids, and reducing dominant macropore sizes, as supported by the SEM and MIP analyses. These results provide quantitative guidance on the use of quicklime and GGBS as stabilisation materials for mitigating loess collapse in pavements.