Comparative Experimental Research On The Impact Of Mechanical Properties Of Concrete Based On The Recycled Coarse Aggregate Classification

Three recycled coarse aggregates is selected in accordance with the national standards in this article. The water-cement ratio of recycled concrete in this article is 0.43, and the replacement rate is 0,50%, 70% and 100%.The impact of the mechanical properties of recycled concrete based on the recycled coarse aggregate classification have been studied on. The mechanical index of three types of recycled concrete about the compressive strength, splitting tensile, shear properties are all have been comparative measured. And finally, macro-mechanical phenomenon regeneration test of recycled concrete were analyzed from the aggregate characteristics, microstructure interface and micro crack development process. So that we can fully understand the impact of the mechanical properties of recycled concrete made by the three types of recycled coarse aggregate.Firstly, concrete test block of 30 cubes and 60 prisms have been made to have pressure testing. The cube compressive strength, axial compressive strength, elastic modulus and stress-strain curve of three types of recycled concrete are have been measured. The relationship between the compressive strength and modulus of elasticity as well as the mathematical models of stress-strain curve have been discussed in this article. The results show that, the compressive strength and elastic modulus of three types of recycled concrete roughly follow the variation of NC＞RCI> RCII> RCIII. The compressive strength decreased with increasing replacement rate. The stress-strain curve of recycled concrete and ordinary concrete are substantially the same. This paper established the equation of a cubic segment of the mathematical models of constitutive relation of the recycled concrete.Secondly,30 test cubes and 30 respectively contour widened section beam have been made to have the splitting tensile and shear test. The splitting tensile strength, shear strength, shear modulus, shear stress-strain curve are have been measured. The relationship between the tensile strength and the compressive strength as well as the shear strength and the mathematical modeling of shear stress-strain constitutive relationship of three types of recycled concrete are all have been discussed. The results show that, the tensile and shear strength of three types of recycled concrete with a large discrete. However, the same type of recycled concrete tensile strength, shear strength decreases with increasing substitution ratio when the replacement rate≥50%. Wherein, the tensile strength, shear strength and shear deformation of natural concrete and recycled concrete II and III which under a low substitution rate (<70%) conditions have a generally good performance. But the tensile strength, shear strength and shear deformation properties of recycled concrete I and recycled concrete II and III which under the high substitution rates (> 70%) are poor. Finally,60 square concrete slab have been test to observe the development of micro-cracks and the surrounding matrix interface of the recycled coarse aggregate near the crack. The interfacial microstructure of three types of recycled concrete has been analysised to better understanding of the macroscopic mechanical properties of concrete. A few comments have been put forward to reinforce the recycled concrete interface at last. Results shows that, there is a new interface transition zone and a old concrete interfacial transition zone in recycled concrete, making recycled concrete interface is relatively complex, especially recycled concrete III. The evolution of crack damage in recycled concrete and the order of the crack development have been concluded by analyzing the weak level of interfacial transition zone in particular weak interface. Combined with the macro-test described in the foregoing to explain the root cause of the differ of macroscopic mechanical properties of the three types of recycled concrete.