Experimental Study On The Behavior Of Largeaggregate Concrete Under Biaxial Dynamic Stress States After Freezing-thawing Cycles

Large aggregate concrete is one kind of concrete which is mainly used to build hydraulic structures such as dams, sluices, docks and so on. Freezing damage is the important factors influencing the durability of hydraulic structures. In addition, both the stress state of concrete and the loading rate should be fully considered in the nonlinear analysis of hydraulic structures. Because concrete in hydraulic structures is usually under complex stress states namely: biaxial and triaxial stress states. And the loading rate is less than 10-5/s usually, but it will be between 10-4/s to 10-2/s when earthquake occurs. Experimental studies on mechanical properties of large aggregate concrete have been preceded by a lot of scholars. These studies are mainly about the uniaxial stress state under static and dynamic loading, biaxial and triaxial stress state under static loading, but most studies are wet-screened concrete. However, the studies of large aggregate concrete about the multi-axis stress state under dynamic loading are less, and the influence of the freezing-thawing cycle effect has not been considered.Dynamic biaxial compressive tests of large aggregate concrete after freezing-thawing cycles and dynamic biaxial tension-compression tests of large aggregate concrete under the normal state are carried out in this article based on the open research foundation of Tsinghua University State Key Laboratory of Hydroscience and Engineering--Study on the multi-axis dynamic strength and failure mechanism of hydraulic concrete after freeze-thawing cycling. The specific researching contents and conclusions are summarized as follows:(1) Freezing-thawing tests and dynamic biaxial compressive tests of large aggregate concrete cube specimen are carried out. The quality loss, damage morphology after different freezing-thawing cycles and the failure pattern, ultimate strength and stress-strain curve under different stress ratios and strain rates are measured. The relationship between freezing-thawing cycles, stress ratio, strain rate and ultimate strength, deformation performance is analyzed according to the test data. The unified failure criterion of large aggregate concrete after freezing-thawing cycles under dynamic biaxial compressive stress state is established respectively in principal stress space and octahedral stress space.(2) Dynamic biaxial tension-compression tests of large aggregate concrete prism specimen are carried out. The failure pattern, ultimate strength and stress-strain curve under different tension-compression ratios and strain rates are measured. The relationship between tension-compression ratio, strain rate and ultimate strength, deformation performance is analyzed according to the test data. The unified failure criterion of large aggregate concrete under dynamic biaxial tension-compression stress state is established respectively in principal stress space and octahedral stress space.(3) Compare the experimental study conclusion of ordinary concrete, wet-screened concrete and air-entraining concrete ultimate strength and failure criteria under biaxial stress state by different scholars with the study results of this article. The results show that large aggregate concrete uniaxial and biaxial compressive strength is 0.7~0.8 times than wet-screened concrete compressive strength. The increasing amplitude of large aggregate concrete biaxial compressive strength compared with uniaxial compressive strength is less than wet-screened concrete. The increasing amplitude of all kinds of concrete uniaxial compressive strength is greater than biaxial compressive strength with the increase of strain rate. Normal concrete and large aggregate concrete biaxial compressive strength loss rate is less than the uniaxial compressive strength loss rate after freezing-thawing cycles. The failure criteria under static and dynamic biaxial tension-compression stress state can be described by straight line and quadratic curve form.