Modified red clay with calcium carbonate: experimental testing and mechanical characterisation

Red clay is characterised as a suboptimal foundation soil due to its high natural moisture content, elevated liquid limit, and significant plasticity. This study investigates the modification of red clay using calcium carbonate. The effects of different types and contents of calcium carbonate were analysed through unconfined compressive strength (UCS) testing, scanning electron microscope (SEM), low-field nuclear magnetic resonance (NMR), and bulk density measurements. The results show that the incorporation of 5% heavy-calcium carbonate (HCC) enhances the UCS and alters the failure mode of the soil. Both HCC and light-calcium carbonate (LCC) affect the boundary moisture content. Furthermore, the bulk density and compaction results demonstrate that the addition of 5% calcium carbonate increases the maximum dry density. The introduction of calcium carbonate also leads to an increase in micropores, which disrupts the original soil structure. Considering the overall improvement effects, a 5% concentration of HCC is determined to be optimal.