Experimental Study On Mechanical Properties Between Steel Bar And Frozen Concrete During Winter Construction

The buildings located in the cold zone are usually destroyed by frozen damage on concrete in winter construction. Temperature change in the pouring concrete stage has a certain impact on the properties of concrete, and inadequate amount of anti-freezing admixture and poor curing condition in low temperature often caused construction problems, such as frost resistance and mechanical properties of concrete decrease. Meanwhile, construction quality is not only important to project period but also influence on the security of building. Rework may cause amount of economic loss. Therefore, it is very important to research the bond behaviour between concrete and steel bar during winter construction.In this paper, the major contributions are summarized as follows by pull-out tests, beam tests as well as theoretical analysis.1. In this study, pull-out tests are carried out to research the bond behavior between steel bar and frozen concrete during winter construction. Test parameters are construction temperature,amount of anti-freezing admixture and curing condition. The typical bond-slip curve obtained and and factors such as ultimate bond strength and bond slip are analyzed compared with specimens in standard curing condition. The research showes that bond properties between steel bar and concrete are degenerated due to inadequate amount of anti-freezing admixture and poor curing condition in low temperature.2.Through the beam tests, the mechanical properties of beam after freezing is studied,and they are analysised by compared with specimens in standard curing condition. The results indicate that the failure mode of the beam specimens is ductile failure. The mid-span deflection of freezed beams is bigger than those of non-frozen specimens. The reason is that machanical properties of beam after freezing degenerate. The bearing capacity of beams changed little, and the frozen ones decrease.3. Based on the results of the pull-out tests, the bond behavior between steel bar and frozen concrete,and degradation mechanism are studied. The load-slip curves, failure mode and mechanical model on friction interface are analyzed to reaserch degrading process. In addition, the load-slip curves of all pull-out specimens are parted four segments to analyze the curves change trend of specimens with different curing condition and admixture.4. Bond-slip constitutive relations can reflect the bond behavior between steel bar and concrete, which provides references to engineering design. Based on the experimental studies, the load-slip curves is compared with CMR mode and continuous mode, and experimental parameters are obtained. The results show that modeled curve corresponds with the test curve greatly. Besides, it may be used as theoretical reference to engineering and provide principles for design code through test results.