Experimental Study On Bending Mechanical Properties Of Recycled Coarse Aggregate Self-Compacting Concrete Beams Under Load-Freeze-Thaw Coupling

With the rapid progress of urbanization,it has driven the rapid development of all walks of life and also spawned a lot of construction waste.In order to reduce pollution to the natural environment and promote a green-friendly society,recycled coarse aggregate self-compacting concrete(Recycled Coarse Aggregate Self Compact Concrete(RCASCC)came into being.Recycled coarse aggregate self-compacting concrete combines the dual advantages of green environmental protection and high performance,which has attracted more and more attention.In recent years,the research on the durability of recycled concrete is a very important direction in recycled concrete,but the research mainly focuses on the durability research under a single degradation factor,and there are few studies on the combined effects of multiple degradation environmental factors.Therefore,in this paper,combined with the unique geographical characteristics of Xinjiang,the durability of RCASCC under the load-freeze-thaw coupling is studied.The specific research contents are as follows:On the one hand,the effect of the number of freeze-thaw cycles on the appearance change,mass loss rate,relative dynamic elastic modulus and basic mechanical properties of the RCASCC test block.Through the freeze-thaw test,the mass loss rate and relative weight of the RCASCC test block after different freeze-thaw cycles were analyzed.The dynamic elastic modulus and compressive strength,splitting tensile strength,and axial compression strength are degraded.At the same time,the stress and strain parameters a and b suitable for RCASCC after freezing and thawing are obtained.The test results show that:(1)the destruction of RACSCC specimens by freezing and thawing is a gradual process,from the initial smooth surface of the specimen to the end of 150 cycles,a large number of aggregates are exposed;(2)different freezing and thawing times there is no obvious difference in the RACSCC failure form.The loss rate of cube compressive strength and the relative splitting tensile strength have a good linear fitting relationship with the number of freeze-thaw cycles;(3)Adopt ordinary concrete uniaxial compressive constitutive equation The constitutive relationship of RCASCC was established,and the a and b values corresponding to the relationship were obtained.On the other hand,the bending test of the RCASCC test beam was conducted.In this test,the number of freeze-thaw cycles and the stress level were used as variables to study the deterioration law of the load effect,freeze-thaw cycle effect and load-freeze-thaw coupling effect on the RCASCC beam.The test results show that:(1)Under the three working conditions,the appearance damage of the RCASCC beam under the load-freeze-thaw coupling is the most serious,and the appearance damage of the RCASCC beam under the load is the smallest.(2)The ultimate load and deflection of L-RCASCC,F-RCASCC and LF-RCASCC beams all decrease with the increase of load(freeze-thaw);(3)The increase of stress ratio can accelerate L-RCASCC,F-RCASCC and LF-RCASCC beam bending failure;It can increase the maximum crack width of the test beam failure,the maximum crack width of LF-RCASCC is increased by 53.8% and 30.4% respectively compared with L-RCASCC and F-RCASCC;LF-RCASCC limit load The ring is reduced by 18.9% compared to L-RCASCC,and the deflection is reduced by 36.4%,indicating that the coupling effect will cause greater damage to the test beam.(4)The bending capacity of LF-RCASCC beam is improved at 0.5 stress ratio.(5)Under the same number of coupling cycles,when the stress ratio is 0.65,the ultimate load reduction of the RCASCC beam is 2.4times that of the SCC beam.