The Experimental Study And Theoretical Analysis On The Mechanical Performance Of Concrete And Bond Behaviour Between Concrete And Steel Bar After Freezing And Thawing

The concrete structures located in the cold region usually are destroyed because of freezing and thawing, and frost resistance is an important aspect of,durability of concrete structure. The frost resistance and mechanic performance of concrete and the bond behaviour between concrete and steel bar will be destroyed after freezing and thawing. It is very important for concrete structure to research the bond behaviour between concrete and steel bar after freezing and thawing. In this paper, the major contributions are summarized as follows by experimental research and theoretical analysis.1,The uniaxial,biaxial mechanic performance of concrete cubic specimens with a size of 100×100×100mm and uniaxial mechanic .performance of concrete cubic specimens with a size of 150×150×150mm are tested after freezing and thawing. The relationship equations between strength of two kinds of concrete specimens and cycles of freeze-thaw cycling are estimated. And the relationship equation of concrete strength of two kinds of specimens is estimated, too. A standard equation is used to descript the stess-strain curve of concrete after freezing and thawing.2,Based on the damage mechanics and Ottosen failure model, a frost damage failure model is established which elastic modulus and Possion ratio under damage are the damage variable. And based on Ottosen theory, a frost damage constitutive model is established and all these will be useful to the development of finite element programme. The test of the constitutive model by the experimental data shows that it is accurate comparatively.3,The pullout specimens of two different surface configurations, three different diameters and three different bond lengthes of stell bars are tested after freezing and thawing by experiments. The effect of freezing and thawing on the bond behaviour is analyzed through the study of these indexes, such as bond strength, slippage at the peak of bond strength, etc. And the effect of surface configurations, diameter of steel bar, bond length of steel bar and concrete strength on the bond behaviour between concrete and steel bar are analized based on the experimental results.4,Theτ-S curves of all pullout specimens are parted four segments to analyze the development ofτ-S curves with the cycles of freezing and thawing increasing. A formula is established to calculate the hydraulic pressure when the concrete under thawing based on the microcosmic mechanic model. Based on the bond-friction model of interface of concrete and steel bar, the mechanism of decreasing quickly of bond strength of plain steel bar after freezing and thawing. Based on the thick-walled column theory, the theoretic model of bond strength of deformed steel bar is obtained. The mechanism of the conversion of failure modes of pullout specimens after freezing and thawing is explained through analyzing the results of experiments and caculating results.5,Based on the theory of macro-damage mechanics, the damage of concrete structures under the action of freezing and thawing may be approximately regarded as the damage due to sequential cyclic action with various positive-negative peak temperature differences, since the temperature difference is always not a constant. On this basis, the reliability of damaged concrete is analyzed. The failure of concrete can be described by the Weibull distribution model. Thereby, a model with 3 parameters for analyzing the reliability of concrete is proposed and the formula for evaluating the residual life of concrete after the freezing-thawing action is deduced.