Effect of curing temperature on hydration and microstructure evolution of cement-based composites with extremely low w/b ratio

The challenge of high geo-temperature often occurred during the construction of deep buried tunnels, and to uncover the effect of varied curing temperature on hydration and microstructure evolution of cement-based composites with extremely low w/b ratio, samples were prepared with a w/b ratio of 0.18 and mixed with different fibers, silica fume and fly ash. Hydration kinetics, main hydration product phases and the evolution of C–S–H inside the samples were analyzed. It was found that the time for maximum heat release peak under 40 °C and 60 °C was earlier than that under 20 °C. The hydration heat of steel fiber composites was lower than that of PP fiber composites. 40 °C curing temperature can motivated the chemical activity of samples and promoted the hydration process, multi-stage peaks appeared at 60 °C curing condition. Q0-Q4 of C–S–H were observed in samples, and the mean silicate chain length (MCL) of C–S–H from 29Si NMR analysis was increased mostly by 15.6% with the elevated curing temperature. This study will provide much support to the safe construction of deep buried tunnels.