Pre-curing time effect on reactive powder concrete impact resistance

To test the effect of pre-curing time on the impact resistance of reactive powder concrete (RPC), RPC specimens were cured in a steam curing box at a temperature of 70 °C for 72 h with pre-curing times of 18, 24, and 30 h. At 28 days, the low-speed impact test was carried out on RPC specimens with a Ceast9350 drop weight impact system at an impact rate of 5 m/s and impact energy of 140 J. The variation curves of the impact force and displacement of RPC specimens with impact times were obtained. The results show that the impact resistance of RPC specimens improved with the increased pre-curing time, implying that appropriate pre-curing time (30 h in this case) can improve RPC mechanical properties. At the same time, combined with x-ray diffraction, scanning electron microscope imaging of hydration products, and the energy dispersion spectroscopy test, the influence mechanism of pre-curing time on the impact resistance of RPC is analyzed from the microstructure standpoint. The results show that appropriate pre-curing time can make the hydration of cement form finer particles and make the hardened paste form a protective structure to reduce the damage of steam curing in the strength development process. Through multiscale homogenization calculation via the Mori–Tanaka scheme, it can be seen that RPC’s stiffness increases with the prolonged pre-curing time. Optimizing pre-curing time is conducive to improving the mechanical properties of RPC specimens.