The Experimental Research On Early Frost Damage To The Performance Of Reinforcement Concrete Member

China is vast in territory, the winter is longer in the cold north area. Constructing in the winter can not only balance the work, but also accelerate the construction of infrastructures. However, the concrete in winter construction may easily be influenced by the cold climate, and the early frost damage will lead to the decline of concrete physical mechanical properties, can not meet the design requirements, and at the same time affect the project quality even lead to serious accidents. At present, there are some researches about the effects of frost damage on concrete self material performance during the construction period, but there are few of reports about the bond-slip behavior between steel bar and concrete under negative temperature. It is not systematically studied about the effects of various factors in early age frost damage on bond-slip behavior between concrete and steel bar, such as concrete strength, temperature during construction period, curing condition, and percentage of antifreeze, etc. Therefore, carrying out experimental research in this area has very important practical significance to the reasonable arrangement of safe winter construction.According to the differences of frost stage, the frost mode of concrete can be broadly divided into three states:new pouring concrete was frozen immediately, concrete with initial strength was frozen, concrete with considerable strength was frozen. The three different modes have different impacts on frost damage to concrete, in which the immediate frost mode is a typical situation of concrete, the damage to concrete is also the most serious. Based on the investigation and research to common construction in winter frost damage and its prevention and control measures, this paper proposed the experiment of early frost damage to the performance of reinforced concrete structures, mainly studied the immediate frost damage to bond performance between concrete and steel bar and the bending performance of reinforced concrete beam in winter natural environmentThe test factors considered the different construction temperatures (normal temperature (20℃),-5℃,-10℃), different curing conditions (Integrative thermal conservation, uncoated curing and nature curing) and different strength grades of concrete (C20, C40, C50). The performance changes of center pull-out specimens of reinforced concrete at-5℃after early age frost damage as well as the flexural property changes of reinforced concrete beam at-10 ℃after the early age frost damage were studied by comparing to the samples at normal temperature. The test results showed that:curing conditions have greater impact on the bond specimen failure modes; the concrete strength, the bond strength between steel bar and concrete had different degrees of loss because of early age frost damage to concrete structure, further more, the lower the concrete strength grade is, the more losses are. Due to early frost damage, the beam's ultimate strength, bending stiffness, ductility all has degradation and the loss of bearing capacity increased with the loss of concrete strength increased.