Effects of nanoparticles on the tensile behavior of ultra-high-performance fiber-reinforced concrete at high strain rates

This study investigated the effects of nanoparticles (NPs) on the tensile resistance of ultra -high-performance fiber-reinforced concrete (UHPFRC), containing 1.5 vol% smooth steel fibers, at both static (0.000167 s-1) and high strain rates (61.86-162.00 s-1). Three types of NPs, namely nano-CaCO3 (3 wt%), nano-SiO2 (1 wt%), and nano-carbon nanotube (CNT) (1 wt%) were considered. All the UHPFRCs containing NPs generated higher rate-sensitive tensile resistance than the UHPFRCs without NPs. For instance, the dynamic increase factor (DIF) for the post -cracking strengths of the UHPFRCs containing nano-CaCO3, nano-SiO2, or nano-CNT was 2.94, 2.79, and 2.69, respectively, while that of the UHPFRCs without NPs was 2.65. The DIFs for tensile parameters of UHPFRCs were dependent upon the types of NPs: nano-CaCO3 produced the highest DIFs for first-and post-cracking strengths, and the number of microcracks, whereas nano-CNT generated the highest DIFs for strain capacities and peak toughness. Besides, the sources of the rate sensitivity of tensile resistances of UHPFRCs containing NPs are closely related to the interfacial bond strengths and compressive strength of matrices.