Influence of High Curing Pressure on the Hydration Process and Multiscale Properties of Concrete

With subterranean excavation engineering being applied to ultradeep geological formations, fresh concrete is cured in a wide range of pressure conditions. However, a lack of understanding regarding the fundamental processes of concrete cured under pressure has hindered further research and related engineering applications. In this study, a series of comprehensive investigations was performed to elucidate the effect of curing pressure (2 MPa, equivalent to a burial depth of approximately 200 m) on the early hydration process and multiscale characterization of concrete system. The results show that under curing pressure, the hydration process was accelerated, specifically in the dormant period (1 h) and acceleration period (0.5 h). The curing pressure condition improved the compressive strength (35.51%) and Young’s modulus (14.85%) and resulted in more brittle characteristics of the concrete. The X-ray computed tomography results showed that the total porosity of the sample decreased by 2.82% with a higher uniformity of slice porosity under curing pressure. Microstructural tests demonstrated that the pressurized sample exhibited a more denser microstructure, better polymerized silicate chains, and a more extensive hydration degree of cement grains. This can be attributed to the conducive effect of curing pressure on the cement hydration and pozzolanic reaction, leading to a more precipitation of hydrates and strengthened microframework.