A review of ground granulated blast furnace slag (GGBS) as a low-carbon alternative for stabilisation of expansive soil

Expansive soils, characterised by significant volume instability due to seasonal moisture fluctuations, pose substantial risks to civil engineering infrastructure. While Ordinary Portland Cement (PC) is a traditional stabiliser, its high carbon footprint and energy consumption necessitate the adoption of sustainable alternatives. This study reviews the efficacy of Ground Granulated Blast Furnace Slag (GGBS), an industrial by-product, as a low-carbon binder for soil stabilisation. GGBS, a latent hydraulic material, requires activation to form cementitious compounds such as calcium silicate hydrate (C-S-H). Research indicates that incorporating GGBS significantly enhances the geotechnical properties of expansive clays, including reductions in the Plasticity Index and the Free Swell Index (FSI) by up to 19.23% relative to untreated clay at a 9% dosage. Mechanical performance is notably improved, with Unconfined Compressive Strength (UCS) gains observed at optimal dosages typically between 10% and 20% and further amplified by extended curing durations. Novel activators such as reactive magnesia (MgO) demonstrate superior efficacy compared to traditional lime or PC, offering enhanced resistance to sulphate and acid attacks. However, a critical knowledge gap remains regarding the long-term durability and microstructural stability of MgO-GGBS-stabilised soils under extreme field weathering conditions, such as repetitive wet-dry and freeze-thaw cycles. This review underscores the potential of GGBS-based binders to promote sustainable ground improvement while highlighting the need for further studies on their environmental longevity.