The research on mechanism of C-S-H nanocrystal improving early properties of shotcrete at low temperature by thermodynamic modelling

In this study, the effect of CSH nanocrystals on the performance of shotcrete are investigated in a low-temperature environment. Setting time and early compressive strength were evaluated for mixtures with different dosages of CSH nanocrystal at 5 degrees C, 10 degrees C, and 20 degrees C. The results show that CSH nanocrystal can shorten the setting time of cement paste mixed with the accelerator, improve the 1 d compressive strength of shotcrete. Meanwhile, the typical samples hydration products and microstructure were determined using XRD, TG/DTG, and SEM, indicate that combined CSH nanocrystal and Alkali free liquid accelerator (AS) can accelerate the cement hydration reaction and promote hydration products AFt, CH, and C-S-H. Moreover, the thermodynamic model (GEMS) simulates the composition change of hydration products of cement paste mixed with CSH nanocrystal and AS at 5 degrees C, 10 degrees C, and 20 degrees C; Confirmed that CSH nanocrystal significantly influences the early hydration products CH, AFt, C-S-H at different curing temperatures, which is similar to the experimental results. Therefore, based on the experimental and simulation results, the synergistic effect of CSH nanocrystal and AS was proposed to solve the problems of a weak early performance of shotcrete and provide a reference for the con-struction of low-temperature shotcrete.