Abstract：Most concrete structure buildings and dams in northern cold region are in complex stress state，and the freeze-thaw cycling has adverse effect on the mechanical properties of concrete. Biaxial concrete tension- compression tests of 4 different stress ratios，0，－0.05，－0.15 and －0.25 after 0，25，50 and 75 freeze-thaw cycles are carried out respectively using the concrete static-dynamic triaxial test system in the State Key laboratory of Coastal and Offshore Engineering，Dalian University of Technology. The strain of two loading directions and the strength of concrete are measured. The strength and the deformation of concrete under different tension-compression stress ratios are studied based on the experiments；and the results indicate that the compressive strength and the tensile strength are decreased with the increasing of freeze-thaw cycles；and that the effect of tension-compression stress ratio on strength and deformation of concrete after freeze-thaw cycling is significant. Failure criterion of concrete under biaxial tension and compression is established in normal stress space and octahedral stress space. The results show that in practical cases，resistance capability against freeze-thaw cycling of concrete structure under biaxial tension and compression is inferior to that of concrete structure under uniaxial stress；and more attention should be paid to this point in structure design.
