Study On Tensile Stress-strain Curve Of Recycled Concrete Based On Meso-scale Model

Recycled aggregate concrete(RAC)is an effective way to solve the pollution of construction waste and protect natural resources,which can be widely used in the projects such as hydralic engineering,ocean,transportation and house building.The tensile stress-strain curve of recycled aggregate concrete is of great significance for analysis on elasto-plastic,damage and fracture mechanisms of concrete structures,and research on ductility and hysteretic behaviors of aseismic structure.In this paper,the water-binder ratio and curing age of RAC are used as variables,and the influence of the water-binder ratio and curing age of RAC on the uniaxial tensile stress-strain curve of RAC,mortar and interface between new mortar and old mortar were analyzed based on the uniaxial tension test carried on the MTS fatigue test machine.Based on the random aggregate model and the experiment,a meso-scale numerical model of the recycled concrete with two interfaces transition zone was established.The effect of the strength and thickness of old mortar on the tensile failure of RAC was analyzed by numerical simulation,and the tensile constitutive model of recycled aggregate concrete was proposed.The results of this research are as follows:1.The compressive strength,tensile strength,elastic modulus and secant modulus at peak stress of RAC decrease with the increase of water-binder ratio,but which increase with the curing period increasing.The tensile strain at peak stress increases with the increase of water-binder ratio,but it decreases with the curing period increasing.The smaller the water-binder ratio,the steeper the ascending and descending stage of the tensile stress-strain curve of RAC.2.With the decrease of the water-binder ratio and the curing age of RAC,the compressive strength,tensile strength,elastic modulus and secant modulus at peak stress of the mortar increase.The smaller water-binder ratio,the steeper the ascending and descending stage of the tensile stress-strain curve of the mortar.On the basis of the experimental results and the Guo Zhenhai's tensile constitutive equation of concrete,the tensile constitutive equation of mortar was proposed.And the calculated curve using mortar equation coincide with the test results,the correlation coefficient R,between the above two is above 0.9.3.With the water-binder ratio of RAC increase,the tensile strength,elastic modulus and secant modulus at peak stress of interface between new mortar and old mortar decrease,and the ascending stage of the tensile stress-strain curve of interface between new mortar and old morta develops more gentle.With the increase of the water-cement ratio of RAC,the strain at peak stress of interface increases and the descending stage of curve becomes steeper at the age of 3 days.The strain at peak stress of interface of 28d decreases with the increase of water-cement ratio,but the descending stage of curve have little change.On the basis of the experimental results and the Guo zhenhai's^tensile constitutive equation of concrete,the tensile constitutive equation of the interface between new mortar and old mortar was proposed.And the calculated curve using interface equation coincide with the test results,the correlation coefficient R2 between the above two is above 0.9.4.Based on the random aggregate model and the material constitutive equations mentioned above,recycled concrete simulation model with two interfaces was established,and the uniaxial tension process of the recycled concrete was simulated by recycled concrete model.The curve of simulation and the experimental curve were basically consistent,it indicates that tensile failure progress of recycled concrete can be simulated accurately by the model.It was found that the damage of recycled concrete under uniaxial tensile load starts from the interface transition zone and then it spreads to the old and new mortar until a final run-through by numerical simulation.When the old mortar thickness is small or the old mortar strength is greater than the new mortar strength,the old mortar on the surface of recycled coarse aggregates has little effect on the tensile properties of recycled concrete.5.Besed on Guo's the tensile constitutive relation model of concrete,the tensile constitutive model of recycled concrete is established based on the experimental results and numerical analysis results.The calculated curve using this equation coincide with the test results,the correlation coefficient R2 between the above two is above 0.8.So the tensile constitutive model of recycled concrete can provide reference for the performance analysis of recycled concrete structures.