Bond slip behavior of light steel and foamed concrete under freeze-thaw cycles

The light steel-foamed concrete composite structure is mainly used in residential building walls and light industrial plant enclosures. In order to investigate the interfacial bond between foamed concrete and cold-formed thin-walled galvanized steel bars exposed to freezing and thawing environments, this paper presents micro-scanning and push-out tests on 23 specimens of neat-cement cellular concrete that does not contain any aggregates. The effects of the number of freeze-thaw cycles, the porosity of the foamed concrete, and the frozen state of the foamed concrete at the time of push-out on the bond-slip properties of the composite structure were analyzed. Surface and internal deterioration of foamed concrete before and after freezing and thawing were also observed. The results indicate that, at the same number of freeze-thaw cycles, higher density leads to increased initial bond stress, peak bond stress, and residual bond stress at the interface of the composite structure. These values increased by 118%~178%, 62%~69%, and 53%~77%, respectively. As the number of freeze-thaw cycles increased, the combined structures of the same density peak bond stress and residual bond stress decreased by less than 14% and 31%. For the same number of freeze-thaw cycles, peak bond stress in the frozen state is 5-8% higher than in the thawed state. It was also found that the higher the density of the foamed concrete, the lower the initial porosity and the greater the resistance to freeze-thaw cycles. A three-stage bond-slip model was developed to account for porosity changes in an ambient environment, and a prediction model for relative bond strength and slip based on freeze-thaw damage was proposed.