Research On Damage Constitutive Relationship Of Recycled Aggregate Concrete

With the rapid development of the economy and the acceleration of urbanization,the use of concrete materials is increasing day by day,and the demand for natural materials such as sand and gravels is also increasing.At the same time,more and more concrete buildings are dismantled due to their inability to meet the needs of use or have reached the end of their service life,resulting in a large amount of construction waste.The extensive treatment of construction waste not only causes waste of resources,but also pollutes the ecological environment.The recycling of construction waste as a recycled aggregate for the production of recycled aggregate concrete is a two-factor method to solve the problem of resource shortage and deal with environmental pollution,which has aroused widespread concern in the engineering community.In order to study the mechanical behavior of recycled aggregate concrete,based on the previous research of the research group,the research on the damage constitutive relation of recycled aggregate concrete was carried out by the combination of experimental research and theoretical analysis.The main work and achievements of this paper are as follows:(1)Based on the stress-strain curves of uniaxial tensile test on recycled aggregate concrete,the evolution equation of tensile damage of recycled aggregate concrete is proposed,and the empirical model of uniaxial tension damage constitutive relation is established.The results show that the damage surface of ordinary concrete is formed by the fracture of coarse aggregate and the interface of aggregate-mortar.The recycled aggregate concrete is mainly formed by the interface of aggregate-mortar.The damage evolution rules of recycled aggregate concrete with different replacement rates are basically the same,but the damage decreases with the increase of replacement rate,because the initial damage of recycled aggregate concrete is not considered.The results of the proposed model agree well with the results of the uniaxial tension test of recycled aggregate concrete.(2)According to the stress-strain curves of uniaxial repeated compression test on recycled aggregate concrete,the plastic strain evolution equation is proposed based on the unloading residual displacement and the compression damage evolution is proposed based on the stiffness degradation of unloading and reloading.And thus the empirical model of uniaxial compression damage constitutive relation of recycled aggregate concrete is obtained.The results show that the compression failure mode of recycled aggregate concrete is oblique shear failure,and the essence of compression damage is the interface slip of shear crack.The proposed plastic strain equation and damage evolution equation agree well with the experimental results.Through the comparison of material test and component test,the proposed model can better reflect the mechanical properties of recycled aggregate concrete.(3)According to the theory of thermodynamics and continuous damage mechanics,the elastoplastic damage constitutive model of concrete under general stress state is derived.Based on the elastic-plastic damage energy release rate,the damage criterion and damage evolution of recycled aggregate concrete are established.The empirical expression of the damage evolution is proposed,and the parameters in the damage evolution rule are calibrated by uniaxial test.The results show that the damage criterion based on the elastoplastic damage energy release rate can better describe the mechanical behavior of recycled aggregate concrete.The damage expression given in this paper can simulate the evolution law of tensile and shear damage of recycled aggregate concrete.