Improvement of Clay Properties with Calcite and Silica Fume: Shear and Unconfined Compressive Strength Focus

This study introduces a novel approach to improve the mechanical properties of clay soil using a combination of calcite and silica fume, addressing the prevalent issues of low shear strength and high compressibility in clay soils that undermine construction stability. This study aims to explore the effectiveness of these additives in enhancing the soil shear strength and unconfined compressive strength (UCS) while analyzing the underlying microstructural changes. The methodology involved field sampling of West Bandung clay soils, followed by laboratory stabilization experiments. The clay samples were treated with 5% calcite and varying silica fume contents (6%, 8%, 10%, and 12%). These mixtures were prepared with the optimal moisture content, cured for 0, 3, 7, and 14 days, and tested using triaxial and UCS equipment. The triaxial test measured the cohesion and internal friction angle, whereas the UCS evaluated the uniaxial load-bearing capacity of the soil. The results demonstrated that the combined use of calcite and silica fume significantly improved clay properties. The internal friction angle increased from 9.90° to 35.31° with 12% silica fume and 14-day curing, indicating an enhanced shear strength. Similarly, the UCS values increased from 0.412 kg/cm² (soft soil) to 1.724 kg/cm² (stiff soil), which is attributed to pozzolanic reactions forming calcium silicate hydrate (CSH) and densification of the soil microstructure. The study concludes that the calcite-silica fume combination is a sustainable soil stabilization method that offers practical benefits for geotechnical applications. The research provides insights into optimizing the additive proportions and curing periods to support infrastructure projects requiring improved ground stability.