Decoding microstructural evolution and mechanical degradation of micaceous granite residual soils as marginal geomaterials in tropical climates

Micaceous residual soil (MRS), a marginal geomaterial commonly found in tropical regions, is often used in low-grade construction projects due to budget constraints. However, little is currently known about its geotechnical properties, especially its long-term environmental response and microstructural variations. Investigated here is how mica content and climate-induced wetting–drying (WD) cycles affect the physical and mechanical properties of MRS. Reconstituted MRS samples with varying mica contents were prepared by mixing muscovite powder with plain residual soil, from which the original mica was removed. These samples were subjected to WD cycles to simulate tropical climate conditions. Geotechnical properties and microstructural changes were analyzed through systematic experimental tests and microscopic observations. The degradation observed during the WD cycles included crack propagation, volumetric swelling, reduced strength, and increased disintegration, all of which were positively correlated with mica content. Notably, for MRS with high mica content, the WD cycles ameliorated the soil brittleness, altering previous perceptions of uniformly low performance for MRS. The effect of mica on MRS under long-term environmental changes is attributed to both the inherent properties of mica and the particle packing structure in the soil. This study enhances the understanding of MRS behavior in tropical climate and provides technical recommendations for further improvement and effective application of this marginal geomaterial.