Comparative Bond-Slip Response of Ribbed Cfrp Bar to Uhpc after Exposure to High Temperature

Ribbed carbon fiber reinforced polymer (CFRP) bar and ultra-high-performance concrete 20 (UHPC) have high potential in terms of utilization of load-carrying capacity and maintenance of the 21 concrete structure. Bonding behavior of ribbed CFRP bars to UHPC after exposure to elevated 22 temperature is of importance due to its susceptibility of thermal effects. This study investigated the 23 residual bond strength of the ribbed CFRP bar embedded in UHPC at ambient temperature and after 24 exposure to elevated temperature. The bond strength of ribbed CFRP bars with different embedded 25 length and cover thickness were also considered and the bond strength was compared with the sand 26 coated CFRP bars. Both at ambient temperature and after exposure to elevated temperature, the bond 27 strength of the ribbed CFRP bar increased with an increased embedment length and cover layer due 28 to the mechanical resistance of the ribs. However, the difference reduced as the elevated temperature 29 increased. Compared with the sand coated CFRP bars, the decreasing rate of bond strength is slightly 30 lower in ribbed CFRP bars and the residual bond strength after exposure to elevated temperature at 31 400 ℃was more than 10 MPa, which satisfies bond strength of FRP bar suggested by ACI 440.5M. 32 The critical temperature of the ribbed and sand coated CFRP bars was suggested as 300 ℃ with 33 consideration of decreasing rate in this study. The modified bond equations were presented to reflect 34 the reduction of bond strength due to the elevated temperature, and the bonding behavior of the 35 ascending branch was compared using the modified BPE and CMR models and presented the 36 coefficient of each parameter.