Ultra-high toughness cementitious composite (UHTCC) shows prominent tensile strain-hardening and multiple-cracking characteristics, can serve as a new type of high performance material used for structure retrofitting and strengthening. The bond between corroded reinforcement and UHTCC has an apparent influence on the mechanical properties of retrofitted structural members. This paper presents an experimental investigation on the bond behavior of corroded rebar and UHTCC through central pullout tests. The experimental results revealed that for rebar with the corrosion ratio in the range of about 10%, the bond strength almost remain identical to that of original rebar whereas about 22% drop was shown for rebar with corrosion ratio of about 14%. At corrosion ratio around 10%, reinforcement with 3d bond length showed 1.5 times bond strength of that with 7d bond length. In addition with the increase in corrosion ratio, the rebar showed relatively high residual bond stress and relatively plump descending branch of bond-slip curve. Furthermore, in comparison with concrete companion samples failing in splitting, all the UHTCC samples failed in pullout due to the fine ductility of UHTCC. Based on experimental results, an empirical model of bond strength between UHTCC and corroded rebar is proposed.
Ultrahigh toughness cementitious composite (UHTCC) is a kind of high performance fiber reinforced cementitious composite (HPFRCC) developed recently, which is optimized based on the micromechanics model proposed by Li and Leung (Li and Leung, 1992). This material is comprised of a cement-based mortar matrix reinforced by 2% high performance polymeric fiber (such as high modulus polyvinyl fiber and polyethylene fiber etc.) in volume or less (Li et al., 1995, 2001; Van Zijl and Wittmann, 2010; Li et al., 2009). Compared with traditional concrete or fiber reinforced concrete (FRC) material, this UHTCC material showed steady-state multiple-cracking propagation (Li et al., 1995, 2001; Li 2002), excellent tensile strain-hardening behavior with ultimate tensile strain above 3% (Li et al., 2001; Li et al., 2009), outstanding crack control capability (Li, 2002; Xu and Zhang, 2009), as well as fine durability including permeability resistance, chloride diffusion, and self-healing capacity (Ahmed and Mihashi, 2007; Van Zijl and Wittmann, 2011).