Effect of High Pressure on the Time-Dependent Rheological Properties of Cement Paste

To improve the understanding of underlying mechanism concerning the change in concrete properties after pumping, the effect of pressure (from atmospheric pressure to 15 MPa) on the time-dependent rheological properties of cement paste was investigated by a rotational rheometer with a high-pressure cell. It is suggested that effect of pressurization on yield stress was mainly related to cement hydration. Under high pressure, cement hydration was accelerated and more ettringite was formed, which resulted in a remarkably increased specific surface area of hydrated cement. Moreover, morphology of hydration products changed under high pressure, and longer rodlike precipitated gypsum was formed, which was disadvantage for improving packing density. The higher specific surface area of hydrated cement, longer rodlike precipitated gypsum, and more mixing water consumed by hydration reduced the average separation distance of particles and increased the relative solid volume fraction, thereby resulting in a significant increase in yield stress of cement pastes.