Bond behavior between steel bar and concrete considering cryogenic temperatures and confinement

Reinforced concrete (RC) structures exposed to cryogenic temperature environment, the bond performance of rebar-concrete is related to the characteristics of concrete material and rebar. The mechanical characteristics of concrete material and rebar vary greatly at cryogenic temperatures. To illustrate the bond behavior of rebar-concrete at cryogenic temperatures, the pull-out speci-mens were simulated focusing on the coupling effects of cryogenic temperatures and confine-ments on the bond behavior. The model considers the surface characteristics of deformed reinforcement and the cryogenic temperature effects on the mechanical characteristics of mate-rials. The confinements were applied to the specimens by carbon fiber-reinforced polymer (CFRP) and stirrup respectively, and the temperature ranges from 20 degrees C to -120 degrees C. The effects of thickness diameter ratio (c/d), and confinements on the bond behavior at cryogenic temperatures were discussed. The results showed that at cryogenic temperatures, the failure modes are similar to those at 20 degrees C for the specimens with c/d <= 3.75. However, for the specimen with c/d = 4.0, the specimen at -120 degrees C exhibits splitting failure due to the increase of brittleness. The bond strength at cryogenic temperatures is improved with the increasing c/d. The effects of confine-ments on the failure modes are small, but the bond strength is improved by the CFRP confine-ments and stirrup confinements. According to the numerical data, the developed bond strength model and bond stress-slip model considering the effects of confinements could provide better predictions of the bond behavior at cryogenic temperatures.