The Effect of Cement Content on the Poroelastic Parameters and Grain Crushing of Artificial Sandstones

Abstract

This study investigates the influence of cement content on the poroelastic properties of sandstones through a series of uniaxial and hydrostatic compression tests under fluid-saturated drained conditions, spanning both elastic and inelastic deformation regimes. Artificial sandstones, made of portland cement, allow precise control over critical structural parameters, including grain size, porosity, and cement content. Hydraulic oil, chosen as the pore fluid due to its higher viscosity compared to water, delays pore pressure response and yields smaller deformation outcomes, closely mimicking realistic conditions. The uniaxial compression tests demonstrate a direct correlation between increased cement content and enhanced mechanical properties, such as uniaxial compression strength, Young’s modulus, and Poisson’s ratio. Specifically, Young’s modulus increases by 1% for each 1% rise in cement content, with uniaxial strength sensitivity to cement content varying according to grain size. Poisson’s ratio is influenced by both the cement content and cement rigidity, but the study reveals that cement content has a more substantial effect on mechanical properties than cement stiffness. A doubling of cement stiffness results in less than a 10% increase in mechanical characteristics. Hydrostatic compression tests were employed to measure drained poroelastic parameters, including bulk modulus and Biot coefficients. These tests identify an inflection point in the bulk modulus corresponding to the critical effective stress for the onset of pore collapse and grain crushing, highlighting the fluid-weakening effect on inelastic properties. The study finds a 30% increase in critical stress for pore collapse with every 20% increase in cement content, while a 1% increase in cement content leads to a 0.5% decrease in the Biot coefficient. Furthermore, the use of the unjacketed bulk modulus for Biot coefficient calculation is shown to consistently underestimate this coefficient. Postcollapse, sandstones exhibit strain hardening behavior, with plastic volumetric strain acting as the hardening parameter.