Effect of temperature on the strength, hydration products and microstructure of shotcrete blended with supplementary cementitious materials

Abstract The effect of temperature on the strength, hydration products and microstructure of shotcrete blended with or without 15 wt% FA, 8 wt% SF, or 15 wt% GBFS are investigated in the range of 20 to 80 °C. The characterization of hydration products, including the type and content of hydration products, C-S-H composition, microstructure and porosity were determined via XRD, Raman spectroscopy, SEM-EDS, and TG. In addition, the hydrate phase assemblages depending on temperature are simulated by thermodynamic modelling (GEMS). The results indicated that the hydration temperature of 40–80 °C promotes a fast hydration of shotcrete with or without SCMs within 28 days. After 28 days, the compressive strength of shotcrete decreases significantly when the curing temperature over 40 °C, however, the compressive strength of shotcrete blended with SCMs does not decrease. Above 60 °C, the porosity of shotcrete with or without SCMs increases after 28 days. At 70 °C, due to the accelerator and increased pozzolanic reaction of the SCMs, the composition of C-S-H of shotcrete with SCMs is shifted towards higher S*/Si, Al/Si, and Si/Ca ratio. In addition, the finer needle-like ettringites with the maximum width between ~0.390 μm and ~0.643 μm at 60–80 °C were observed. The observed variations of the phase with temperature are confirmed by the thermodynamic model.