Microscopic mechanism of sandstone hydration in Yungang Grottoes, China

Abstract

The macroscopic engineering properties of sandstone are dominated primarily by mineral features in a microscopic scale. This study will investigate the microscopic physical and mechanical properties of the main minerals (quartz, K-feldspar, Na-feldspar and kaolinite) in Yungang Grottoes sandstone, using the molecular mechanics and the molecular dynamics simulations. The microscopic physical properties were represented by density and volume. The microscopic mechanical properties were represented by Young’s modulus and Poisson’s ratio. The microscopic mechanical properties of the minerals in various directions were then explored. The influences of water molecules and the surrounding temperature on the microscopic physical and mechanical properties of the minerals were furthermore investigated. It is found that the differences in the microscopic densities between the simulated results and those from the open data set are, respectively, 0.37%, 1.15% and 9.16%, for the quartz, Na-feldspar and kaolinite cells; the microscopic mechanical properties of various minerals have a significant anisotropy; the Young’s modulus of halloysite decreases by 75.86% compared with that of kaolinite; as the water molecule number increased from 0 to 5, the Young’s moduli of K-feldspar, Na-feldspar and kaolinite cells decreases by 31.31%, 55.05% and 42.60%, respectively; for each mineral, as the temperature increases from 243.15 to 303.15 K under one atmospheric pressure, the volume increases and the density decreases. Those results may have a theoretical significance for the analysis of microscopic mechanism of hydration in the Yungang Grottoes sandstone.