Study On The Strength Of Air-entraining Concrete Under Multiaxial Stress States After Freeze-thaw Cycling

Experimental study on multiaxial characteristic of air-entraining concrete after freeze-thaw cycling is just in the initial stages. Presently, there are quite few researches in this field, and most of the experiments and theory studies are focused on the uniaxial stress conditions. Practically, a majority of structures is generally working under the multiaxial stress states. As a part of the project of National Nature Science Foundation named "multiaxial stress and failure criterion of concrete in freeze-thaw environments"(50479059), the surface-stripping configurations of air-entraining and no-air-entraining concrete after freeze-thaw cycling are described, and the experimental researches and theory studies on the uniaxial strength and multiaxial strength of air-entraining concrete are carried out. Main research contents in this paper are listed as follows:(1) After different freeze-thaw cycles, the surface forms of air-entraining concrete and no-air-entraining concrete are compared and analyzed, and the result of microcosmic configuration of air-entraining concrete tested by electron microscope is reported simultaneously.(2) Uniaxial compression experiments are made on the air-entraining concrete specimens with different design compressive strength under normal environment and after different freeze-thaw cycles. The failure patterns of concrete are described. Relationship between the decreasing percents of strength of concrete and the freeze-thaw cycles is analyzed. Simultaneously, a formula to describe the relationship between the strength of concrete and freeze-thaw cycles is given.(3) Biaxial compression experiments and biaxial tension-compression experiments with equal proportion loadings are carried out on the air-entraining concrete specimens, the target compressive strength of which is C30, under normal environment and after different freeze-thaw cycles respectively. The results are brought out with the descriptions of the failure patterns of concrete together with the relationships between the amplitude of variation of strength of concrete and freeze-thaw cycles, as well as the stress ratios. Furthermore, the relationships between the stress ratios, the freeze-thaw cycles and strength of concrete, are also anal(?)zed. Based on it. failure criterions under biaxial compression and (?)iaxial tension(?)osed respectively.(4) Triaxial tension-compression-compression experiments on the strength of concrete after freeze-thaw cycling are executed. The failure patterns of concrete are described. The influence of the mid-stress to the strength of concrete is analyzed. Taking freeze-thaw cycles and stress ratios into account, a failure criterion in octahedral space is suggested.