Research On Meso-damage Properties Of Recycle Concrete Based On Aggregate Substitution Rate

Due to the huge demand for concrete,sand and gravel resources as its raw materials are becoming scarce.At the same time,the construction of new buildings and the demolition of old buildings generate a large amount of construction waste.Waste concrete after being processed and reconfigured into recycled concrete can relieve the pressure caused by the above current situation.Due to the existence of recycled aggregates,the mechanical properties of recycled concrete are weaker than ordinary concrete,and the micro structure of recycled concrete is more complicated than ordinary concrete.The finite element simulation method can realize in-depth research on the meso-damage performance of recycled concrete from a meso-level perspective.The self-edited program in this paper established a two-dimensional meso-structure of recycled concrete composed of five-phase materials including new hardened mortar,old hardened mortar,internal interface zone,external interface zone and natural aggregate,and carried out a series of recycled concrete with different aggregate replacement rates.The mesoscopic study of the research has studied the influence of the strength of the meso-phase materials on the macro-mechanical properties of concrete under different substitution rates.The specific research work is as follows:(1)Establish a two-dimensional meso-structure of recycled concrete composed of five-phase materials including newly hardened mortar,old hardened mortar,internal interface zone,external interface zone and natural aggregate.Based on the concrete damage plasticity constitutive model and the Monte Carlo method,a two-dimensional recycled concrete random aggregate program was written in Matlab language,the aggregate coordinate information was extracted,and the model was imported into Abaqus using a Python script,and the aggregate replacement rate was established respectively 0,30%,50%,70%,100%recycled concrete two-dimensional random aggregate model,this method realizes the effective simulation calculation of recycled concrete by Abaqus software,the randomness of aggregate particle size and the randomness of aggregate distribution The performance is good,and the aggregate is evenly distributed in the injection area without accumulation,which can meet the requirements of numerical simulation.Importing models into Abaqus using Python scripts greatly shortens modeling time and improves modeling efficiency.(2)Numerical tests of uniaxial tension and uniaxial compression are carried out on the two-dimensional random aggregate model of fully recycled concrete.The results show that the stress distribution of recycled concrete is consistent with the evolution of the damage zone,which is consistent with the final failure form of the cube test.Under uniaxial compression,the damage zone develops in the direction of 45°.Under uniaxial tension,the damage zone is perpendicular to the The direction of the external load develops laterally.By comparing the simulation results with related experiments,the reliability of the calculation model is verified.(3)Numerical tests of uniaxial tension and uniaxial compression are carried out on recycled concrete with different replacement ratios.The results show that the stress-strain curve of recycled concrete is similar to the stress-strain curve of ordinary concrete.The uniaxial tensile and compressive strength of recycled concrete decreases with the increase of aggregate replacement rate,and the strain increases with the increase of aggregate replacement rate.Decline.Compared with ordinary concrete,the uniaxial tensile strength of recycled concrete is reduced by 5%to 13%,and the uniaxial compressive strength is reduced by 2%to 11%.The damage evolution law of recycled concrete with different replacement rates is as follows:the initial damage first appears in the transition zone of the inner interface,and then the damage appears in the transition zone of the outer interface,and the damage develops to the old hardened mortar zone.The aggregate spreads to the newly hardened mortar area,and finally reaches the limit of destruction.Under uniaxial tension,the damage zone develops laterally,and under uniaxial compression,the damage zone develops obliquely.(4)The variable parameter analysis of the meso-material strength of each phase under different aggregate replacement rates shows that for ordinary concrete,the strength of the new interface transition zone has a significant strengthening effect on the tensile and compressive properties of the specimen.For recycled concrete,the strength of the transition zone of the internal interface and the strength of the old mortar have a significant strengthening effect on the specimens.Under uniaxial tension,increasing the strength of the transition zone of the inner interface by 20%can increase the tensile strength by 10%～15%,and increasing the strength of the old mortar zone by 20%can increase the tensile strength of recycled concrete by 10%～14%,replacing aggregate The strengthening effect is most obvious when the rate is 70%.Under uniaxial compression,increasing the strength of the transition zone of the inner interface by 20%can increase the compressive strength of recycled concrete by about 15%,and increasing the strength of the old mortar zone by 20%can increase the compressive strength of the specimen by about 10%.