Post-fire Bond Behaviors Between Grout and Steel Rebar

Firstly, according to the theoretical analysis, the force mechanism and failure modes were assured for the bond behavior between grout and steel rebar. Then, a pull-out experiment was exerted to probe the bond behavior developments of specimens after exposed to 500 °C. It is found that the mixed measures of pre-drying and slow elevating rate, i.e., 5 °C/min, inhibits the explosive spalling in grout with compressive strength of 76.7 MPa. In addition, there are two failure modes including the steel rebar fracture and the bond slip failure in the test. Based on the elevated temperature, compressive strength of post-fire grout, diameter of steel rebar and its embedment length, a new expression has been built to calculate the bond strength between grout and steel rebar of post-fire specimens. Furthermore, the finite element simulation is employed to investigate the bond behaviors of pull-out specimens after exposed to elevated temperatures up to 500 °C. The steel rebar fracture is captured firstly in the pull-out test simulation. Moreover, it is found that the peak slips increase and peak loads decrease along with the temperature elevating. Finally, it is proposed that the crucial elevated temperatures of the failure mode change should be 300, 300 and 400 °C for the specimens with embedment lengths of 6, 7 and 8 times diameter of steel rebar with diameter of 16 mm, respectively, which is beneficial for evaluating the fire safety of the existing structure elements.