Study on the Mechanical Properties and Microstructural Mechanisms of Limestone Calcined Clay Cement-Stabilized Soft Soil

High water-content silty soft soils are widely distributed across coastal regions. Their low strength and high compressibility render them unsuitable for direct use as foundation or subgrade materials. While ordinary Portland cement is the most prevalent chemical stabilizer for ground improvement, its manufacturing process generates substantial CO2 emissions, significantly exacerbating global climate change. While limestone calcined clay cement (LC3) has emerged as a promising low-carbon alternative in concrete engineering, its multicomponent hydration mechanisms and engineering applicability for geotechnical soft soil stabilization remain a critical knowledge gap. To address this, this study investigates the application of LC3 in ground improvement by systematically evaluating and comparing three novel LC3 blends formulated with distinct types of calcined clay. The mechanical properties of LC3-stabilized soft soil were investigated through unconfined compressive strength and direct shear tests. Furthermore, the underlying stabilization mechanisms and microstructural evolution were revealed using X-ray diffraction and supplementary microanalytical techniques. The results demonstrated that LC3 significantly enhanced the mechanical properties of soft soils by generating abundant C-S-H and C-A-S-H gels, which bound soil particles into a stable, interlocking network. Among the evaluate variants, the calcined kaolin-based cement (LC3-K) exhibited the highest pozzolanic activity, providing to be the optimal stabilizer. However, this stabilization effect was dosage dependent; while an appropriate LC3 application markedly improved soil strength, excessive dosage or elevated clinker proportions induced a highly alkaline environment. This led to charge over-neutralization and deflocculation, ultimately compromising the structural integrity and mechanical performance of the solidified soil. The findings of this study provide a solid theoretical foundation for the application of eco-friendly LC3 in soft soil stabilization, promoting the broader adoption of sustainable, low carbon geomaterials in geotechnical engineering.