Discrete Element Study On Axial Compression Performance Of Recycled Concrete

The development of the construction industry,while promoting the rapid economic growth,has also seriously damaged the social ecology and environment.The reuse of waste concrete has significant environmental,economic and social benefits.Relevant studies show that although the physical and mechanical properties of reclaimed concrete are not as good as those of primary aggregate,the physical and mechanical properties of reclaimed concrete can be effectively improved by adding various admixtures,shaping of reclaimed aggregate,reducing water-cement ratio and two-stage mixing method.Therefore,as a kind of sustainable green building materials,recycled concrete has a good application prospect.At present,there have been a lot of researches on the mechanics,fatigue,durability and improvement of recycled concrete,but its engineering application is still limited to non-structural components.There may be many reasons,but the most critical one is:the existence of recycled aggregate attached to old mortar brings more complex mesostructure to recycled concrete,but also increases the uncertainty of its macroscopic mechanical properties.Therefore,it is very important to study the influence of each component on the overall mechanical properties of recycled concrete from the mesoscopic level.Based on this,it is also considered that it is difficult to ensure that each phase has a single and stable variable(such as the thickness of the attached old mortar layer,the diffusion performance and thickness of the transition zone between the new and old interface,crack distribution,etc.)in conventional experiments.In order to reveal the failure mechanism of recycled concrete,it is necessary to study the mechanical properties of recycled concrete from the mesoscopic level.Therefore,in this paper,particle flow discrete element is used as the research method,laboratory test and numerical simulation are combined to establish a numerical model of recycled concrete,and the effects of various components of recycled concrete,aggregate distribution and loading speed on the mechanical properties of recycled concrete are discussed from the mesoscopic simulation.(1)Based on the experiment,the program of 2D random aggregate placement is designed by using matlab software.Random aggregate is generated according to the gradation,and the random aggregate model generated by extracting the radius,position and boundary information of aggregate is imported into CAD.Then the CAD aggregate model is imported into PFC software to obtain the 2D recycled concrete random aggregate model.(2)Based on the macroscopic parameters of new mortar,old mortar,aggregate,concrete and recycled concrete tested in the laboratory,the microparameters of each group used for simulation were inverted,and the particle flow discrete element calculation model was established.By attenuating the bonding parameters between old and new mortar in the numerical model of particle flow discrete element reclaimed concrete,the strength parameters of transition zone of various surfaces are obtained by multiplying the attenuation coefficient.(3)The stress-strain curve of macro-reclaimed concrete was compared with the simulation,and the macro-compressive strength,elastic modulus,Poisson’s ratio and tensile strength were fitted to reproduce the whole process of crack initiation,development and penetration of reclaimed concrete under axial compression,which provided a reference for the subsequent research on the failure mechanism of mesostructure of reclaimed concrete.(4)Under the condition that the parameters of each component of recycled concrete are obtained,the thickness of old mortar,aggregate distribution and loading speed of recycled concrete are discussed,and the influence of different factors on the uniaxial compression performance of recycled concrete under different conditions is discussed,as well as the whole process of initiation,development and extension of micro-cracks to penetration under different conditions.The influence of different factors on recycled concrete is analyzed step by step.It provides some reference for the subsequent research on the failure mechanism of the meso-structure of different components of recycled concrete.