Bending Toughness and Calculation Model of Ultrahigh-Performance Concrete with Hybrid Micro- and Nanofillers

Abstract

Superfine stainless wires (SSWs) and carbon nanotubes (CNTs)/nano SiO2-coated TiO2 (NTs) were used as hybrid micro- and nanofillers to toughen reactive powder concrete (RPC) in this paper. The multiscale synergistic toughening mechanisms of micro- and nanofillers were revealed through theoretical calculation. Experimental results show that incorporating 1.2% by volume SSWs and 1.5% by weight NTs enables the three-point bending strength, first-cracking strength, and bending toughness of RPC to increase by 171.6%, 96.0%, and 572.1%, respectively. The numbers of SSWs being pulled-off at failure are increased by 19.1%, resulting from the addition of nanofillers reducing original flaws and enhancing the interface of SSWs through a nanocore effect at the nanoscale. Meanwhile, the widely distributed core-shell elements and SSWs work together to effectively inhibit the initiation and propagation of cracks by pinning and bridging effect at the microscale, leading to the bending strain-stress curves of RPC with hybrid fillers to have significant strain-hardening and slow strain-softening stages.