Shear impact resistance of nanoparticle-incorporated ultra-high-performance fiber-reinforced concrete at high strain rates

Abstract

This study investigates the effects of incorporating nanoparticles (NPs) on the shear impact resistance of ultra-high-performance fiber-reinforced concrete (UHPFRC) containing 1.5 vol% straight steel fibers. Two NPs, nano-CaCO3 and nano-SiO2, were added at 3 and 1 wt% of cement weight, respectively. In particular, this study focuses on shear behavior at both static and high strain rates, which has been less investigated compared to compressive and tensile responses. NPs incorporation significantly improved the shear resistance of UHPFRC at both static and high strain rates. At a static strain rate (γ˙ = 6.7 × 10−4 s−1), UHPFRC incorporated NPs exhibited approximately twofold increases in average shear strain capacity and energy absorption capacity compared to the UHPFRC without NPs. NPs incorporation substantially increased strain rate sensitivity at high strain rates. As the strain rate increased from 6.7 × 10−4 to 239.5 s−1, the average shear strength, shear strain capacity, and energy absorption capacity of UHPFRC containing 3 wt% nano-CaCO3 increased from 21.6 to 38.2 MPa, 8.97% to 23.9%, and 144.82 to 488.56 MPa-%, respectively. Among the investigated NPs, nano-CaCO3 confirmed superior performance. Nanoindentation results revealed that nano-CaCO3 increased the hardness and elastic modulus of the C–S–H phase in the fiber–matrix zone, contributing to enhanced shear resistance. Overall, a consistent linkage between microstructural enhancement and macroscopic shear performance and rate sensitivity was established, and nano-CaCO3 was identified as the most effective nanoparticle for improving the shear impact resistance of UHPFRC under extreme loading conditions.