Experimental Study On Stress-strain Curve Of Recycled Coarse Aggregate Concrete Under Uniaxial Tension Load

For the surface of recycled coarse aggregate is adhered with a layer of old mortar,so that the coarse aggregate concrete interface performance of recycled coarse aggregate concrete is complex,and therefore,the performance of recycled coarse aggregate concrete is different from that of ordinary concrete.The study of axial tensile constitutive relation of concrete is indispensable for its material and structural properties.However,the test methods of stress-strain curves of recycled coarse aggregate concrete under uniaxial tensile load are not uniform,so the axial tensile properties of recycled coarse aggregate concrete cannot be evaluated scientifically.Based on the comparison of the existing test method of ordinary concrete under uniaxial tensile,the unnotched test method for stress-strain curve of the recycled coarse aggregate concrete under uniaxial tensile load was applied.Besides,the characteristic parameters of stress-strain curves of recycled coarse aggregate concrete under uniaxial tensile load were studied.And the effect of recycled coarse aggregate replacement rate,the content of fly ash and the proportion of slag and fly ash on the stress-strain curve of recycled coarse aggregate concrete under uniaxial tensile load was studied,the results of the study showed that:1.The test method of stress-strain curves of recycled coarse aggregate concrete under uniaxial tensile load was adopted in this paper,which is an effective method and has the advantages of simple operation,convenient manufacture,uniform specimen tensile process stress,and the stable test results.2.The compressive strength,tensile strength,initial elastic modulus,and peak deformation modulus of recycled coarse aggregate concrete were slightly lower than that of ordinary concrete.The peak strain of recycled coarse aggregate concrete was slightly higher than that of ordinary concrete.The replacement rate of recycled coarse aggregate nearly didnot affect the compressive strength,tensile strength,ultimate tensile strain,initial elastic modulus,and peak deformation modulus of recycled coarse aggregate concrete.3.The compressive strength,tensile strength,ultimate tensile strain,and initial elastic modulus of recycled coarse aggregate concrete with single fly ash at early age decreased with the increase of fly ash content.When the fly ash content is over 10 percent of binder,the ultimate tensile strength,initial elastic modulus,and peak deformation modulus of 7d and 28d of recycled coarse aggregate concrete decreased with the increase of fly ash content,.In addition,the tensile peak strain was not influenced by changing fly ash content.4.When the fly ash-slag ratio is 1:2,the compressive strength,tensile strength and initial elastic modulus,peak deformation modulus of recycled coarse aggregate concrete are highest.The changed mixed ratio had little influence on the peak strain of coarse aggregate concrete,and the compressive strength of recycled coarse aggregate concrete mixed with slag and fly ash was higher than that of basic group.The optimum property of recycled coarse aggregate concrete under uniaxial tensile load can be obtained,when the fly ash-slag ratio is 1:2 under 30%mineral admixture content.5.Based on the above test results and ordinary concrete tensile constitutive mode,the constitutive model of recycled coarse aggregate concrete under uniaxial tensile load was established.The model parameters value of the equation ascending part is between 0.95?1.25,correlation coefficient R2 of which is between 0.97?0.99.Descending parameter ? values is between 1.5?10.The relationship between parameter a and tensile strength is a = 0.625ft2,and the correlation coefficients R2 of which is between 0.81?0.99.It could meet the need of engineering precision,which provided a basis for the research on the mechanical properties and durability of the recycled coarse aggregate concrete structure.