Study On Micromechanical Properties Of Recycled Concrete With Different Aggregate Shapes

The rational utilization of recycled concrete can reduce the proportion of waste concrete,and reduce the consumption of natural resources.The traditional macro test is time-consuming and labor-consuming,and it is difficult to see the interaction and meso failure characteristics of various materials in recycled concrete under external load.Therefore,in this paper,a meso numerical model of six phase recycled concrete with different shapes composed of new mortar,old mortar,three interface areas and recycled aggregate is constructed by using Python language combined with random theory to study the mechanical properties of six phase materials and the influence of their interaction on the overall mechanical properties.The specific research work is as follows:(1)Combined with Monte Carlo random theory,fuller grading theory and wallavin formula,the program algorithm of the generation and delivery process of three different shapes(circular,elliptical and polygonal)aggregates is systematically compiled by using PYTHON language.The two-dimensional meso calculation models of recycled concrete with different shapes is constructed,which is composed of six phase materials of random aggregate,old mortar,new mortar,aggregate-old mortar interface(OITZ1),old mortar-new mortar interface(OITZ2)and aggregate-new mortar interface(NITZ).The correctness and rationality of the random aggregate algorithm are verified by three parameters:coarse aggregate release rate(40%-60%),recycled aggregate replacement rate(20%-70%)and random number(4 times).(2)Import the numerical model into ABAQUS software and call Python script,select CDP model,and calculate the parameters such as stress,inelastic strain,cracking strain and damage factor of CDP model in combination with sidoroff energy equivalence principle.Considering the influence of random number,9 groups of models are constructed,the uniaxial compression(tensile)displacement load(18 groups of simulated working conditions)of circular,elliptical and polygonal random aggregate recycled concrete models are calculated and analyzed respectively.The calculated cloud diagram damage state of each calculation model is "V" shape("I" shape).The failure form of the whole model conforms to the development law of the test,which verifies the rationality and correctness of the model.The order of compressive(tensile)strength of models with different aggregate forms is as follows:polygonal aggregate model>elliptical aggregate model>circular aggregate model.Through the comparative analysis of three random aggregate models with different shapes,it is considered that the random polygonal aggregate model is more suitable for the real aggregate model and is more suitable for further study of its micromechanical properties.(3)By designing three groups of meso numerical models of random polygonal aggregate recycled concrete with different parameters such as tensile strength of new mortar,tensile strength of old mortar and thickness of old mortar,the evolution curve of strain field of each component element and the evolution curve of stress-strain field of the whole model are measured,The results show that the improvement of the tensile strength of the new mortar has a great impact on the mechanical properties of the model sample.With the improvement of the tensile strength of the new mortar,or when the tensile strength of the old mortar is close to that of the new mortar,the peak strength of the recycled concrete model sample is relatively greatly improved.(4)The algorithm of random polygonal aggregate recycled concrete model is optimized twice,and four meso polygonal aggregate models with substitution rates of 30%,50%,70%and 100%are established.Under uniaxial compression(tensile)displacement load,the damage development process of random polygonal aggregate recycled concrete model under different substitution rates is simulated,By analyzing the changes of peak stress and peak strain of each model,it is found that the mechanical properties of random polygonal aggregate model with substitution rate less than 50%are relatively better.