Strength enhancement of expansive and non-expansive clays using colloidal silica

Faculty of Science and Engineering, Macquarie University, New South Wales, Australia

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Abstract

Expansive and soft clays pose major challenges in infrastructure development due to their high compressibility, low shear strength, and significant volume changes upon wetting and drying. Conventional cement-based stabilisers are effective but carbon-intensive, motivating the search for sustainable alternatives. Colloidal silica (CS) has emerged as a sustainable, low-carbon alternative to traditional cementitious binders for stabilising problematic soft soils. This study investigates the potential of CS to improve the unconfined compressive strength of both expansive (Bentonite) and non-expansive (Kaolinite) clay samples. The gelling time results show that increasing CS concentration and the presence of NaCl significantly reduce gelation time, while bentonite–CS mixtures gel faster than kaolinite–CS mixtures due to higher surface activity and cation-exchange capacity. Laboratory experiments were conducted at 30% CS and 15% NaCl concentrations with two curing periods of 7 and 14 days to evaluate changes in unconfined compressive strength (UCS). Kaolinite exhibited approximately 50–55% increase in peak strength between 7 and 14 days of curing, while bentonite showed about 20–25% higher UCS than kaolinite under identical treatment conditions. The findings demonstrate that CS is an effective and environmentally friendly stabiliser that can improve both expansive and non-expansive clays, making it a promising alternative for sustainable ground improvement applications.