Stabilisation of high-water content organic and inorganic very soft clays using alkali-activated ground granulated blast furnace slag

Soft clays exhibit low shear strength and high compressibility, and the presence of organic matter further increases their sensitivity and susceptibility to secondary consolidation. Chemical stabilisation of these soft clays with high organic content using conventional binders such as lime and ordinary Portland cement (OPC) is widely reported to be ineffective. On the other hand, alternative cementitious materials such as alkali-activated materials (AAMs) offer a promising and more sustainable approach for improving their engineering performance. In this study, the stabilisation of very soft organic (O) and inorganic (I) clays with high natural water content using AAMs was investigated. A novel sample preparation approach with AAMs was proposed for the stabilisation of these clays. The influence of clay mineralogy, organic content, water content and activator molarity on the effectiveness of stabilisation was investigated using mechanical and microstructural characterisation. Unconfined compressive strength (UCS) and plasticity characteristics of stabilised soft clays were determined at different curing periods. The results indicate that the UCS values of AAM-stabilised soft clays increased with an increase in curing period and activator molarity, suggesting that AAMs are effective in stabilising soft clays with high natural water content. Microstructural characterisation, using TGA, FTIR, QXRD and SEM, was carried out to elucidate the mechanism of AAM stabilisation. TGA and QXRD studies confirmed the formation of hydration products, such as C-S-H, hydrotalcite, stratlingite and silicocarnotite in stabilised soft clay samples that contributed to the enhanced mechanical performance. QXRD studies further indicate the participation of clay minerals in alkali-activation, thereby resulting in microstructural densification and improvement in mechanical performance. The amount of bound water, which reflects the hydration products, obtained from TGA analysis also corroborates the UCS values; the samples with higher bound water content exhibited higher UCS values. Overall, this study demonstrates that the proposed sample preparation approach using AAM is effective in chemically stabilising very soft organic and inorganic clays with high natural water content.