Experimental Study On Stress-strain Relationship Of High Strength Concrete With High Admixture Under Uniaxial Compression Under Salt Freezing Conditions

The coastal concrete structures in cold regions are generally affected by freeze-thaw and chloride salts.Freeze-thaw damage under salt-freezing conditions seriously affects the physical-mechanical properties and durability of concrete materials,greatly reduces the safety of concrete structures and shortens their service life.In this paper,the effects of freeze-thaw cycle times and admixture content are considered,and the mechanical properties and constitutive relation of high-concrete C60 high-strength concrete under salt-freezing environment are studied experimentally,and the theory of the constitutive relation of freeze-thaw damage concrete is enriched and perfected,which provides a theoretical reference for the bearing capacity design and finite element analysis of concrete structures.The main work of this article is as follows:(1)A total of 42 concrete cube standard specimens and 84 prismatic standard specimens were prepared.The freeze-thaw cycles of 100,200,250,300,350,and 400 freeze-thaw cycles were performed in a salt-freezing environment.After the freeze-thaw cycle,the apparent damage of the specimen was observed.The mass loss,dynamic elastic modulus,and cube compressive strength were measured.The variation of compressive strength with the number of freeze-thaw cycles for the different blended high-strength concrete cubes was studied.The relationship between relative dynamic elastic modulus and cubic compressive strength was fitted and the fitting was good.Relative dynamic elastic modulus was introduced in the formula.The results show that: the compressive strength of each batch of concrete decreases linearly with the increase in the number of freeze-thaw cycles,but the compressive strength of the concrete test blocks in the FA group tends to be gentler than that of the FB.(2)After the freezing and thawing cycles,the uniaxial compressive stress-strain tests were performed on the concrete prismatic specimens,and the uniaxial compressive failure morphology of different blended high strength concrete specimens after salt freezing was analyzed.The experimental curve of uniaxial compression stress-strain relationship before and after salt freezing was measured by appropriate experimental methods and data acquisition system.The peak compressive stress,peak compressive strain,elastic modulus and cycles of freeze-thaw cycles were fitted using least squares theory.The relationship between them is well fitted.The results show that the trend of the stress-strain curve of two batches of high-mix concrete high-strength concrete specimens under the action of gas-frozen air-melting cycles is approximately the same.(3)The two section curve equation proposed by Professor Guo Zhenhai is used to fit the full curve of the uniaxial compression stress strain of the prism,and the fitting formulas of the parameters of the curve rising and descending section and the number of freezing and thawing cycles N are obtained,and the fitting situation is good.The results show that the use of sectional constitutive equation can well simulate the stress-strain curve of uniaxial compression with different blending amount of high-strength concrete,and provide a reliable basis for nonlinear analysis of high-strength concrete admixtures.