Damage evolution characteristics of siliceous slate with varying initial water content during freeze-thaw cycles.

Comprehensive studies on the freeze-thaw (F-T) damage mechanism in siliceous slates are lacking. In this study, we investigated the evolutionary characteristics of F-T damage in siliceous slates. To this end, scanning electron microscopy, X-ray diffraction, X-ray fluorescence, and uniaxial compression tests were used to analyze the microstructure, phase composition, porosity, and macroscopic mechanical parameters of siliceous slate with varying initial water content during F-T cycles. The results revealed several insights. (1) The microstructure of siliceous slate undergoes significant change with respect to increasing water content and number of F-T cycles. The rock surface changed from smooth to rough, and the arrangement of the mineral particles changed from tight to loose. (2) More than 80 % of the contents of siliceous slate comprise oxygen, aluminum, silicon, potassium, and iron. In particular, siliceous slate comprises muscovite, quartz, clinochlore, and kaolinite. Both the clinochlore and kaolinite are unstable clay minerals. As clay minerals exhibit strong water absorption and expansion characteristics, kaolinite undergoes strong hydration reactions. Compared to rock samples without F-T cycles in the dry state, the clay mineral content of siliceous slate decreased by nearly 50 %, from 28.8 % to 15.5 %, after 30 F-T cycles in the saturated state. (3) The mechanical parameters of siliceous slates with varying water content decreased exponentially with the number of F-T cycles, while their porosity exhibited a positive correlation with the number of F-T cycles. The degree of deterioration in both increased with increasing water content. Both the number of F-T cycles and the initial water content were observed to wield a significant effect on the deterioration of siliceous slates. (4) The evolution curve of F-T load damage in siliceous slate exhibited characteristics of transitioning from gentle to concave and then to a convex stage of growth. Our results are expected to provide theoretical guidance for the evaluation and prevention of F-T disasters in cold regions.