Hydration kinetics and strength retrogression mechanism of silica-cement systems in the temperature range of 110 °C–200 °C

A comprehensive investigation of silica-cement hydration kinetics and engineering properties in the temperature range from 110 °C to 200 °C and pressure range from 25 MPa to 50 MPa were conducted by isothermal calorimetry, chemical shrinkage, and ultrasonic cement analyzer. Test results revealed that the effect of curing temperature on the hydration kinetic profiles is very complex, while the influence of pressure is relatively evident. The heat of hydration of the silica-cement system is approximately proportional to chemical shrinkage and the proportionality constant is invariant with curing temperature. Strength retrogression of silica-cement systems is caused by the transformation of amorphous C-S-H to xonotlite and tobermorite and is accompanied by volume expansion possibly due to the conversion of chemically bound water to free water. Increasing curing pressure can accelerate the volume expansion and phase transformation process during early age, while increasing silica dosage can significantly slow down such process.