Study On The Mechanical Properties Of Recycled Concrete And Numerical Simulation

Under the background that the resources of building materials are getting poorer and the environmental protection is increasingly strengthened,the recycling and utilization of construction waste has become one of hot research issues with the most social,economic and environmental value.Among them,recycled preparation of concrete waste and mechanical properties test of recycled concrete is also an important content of recycling application research.In view of this,combined with the means of experimental study and numerical simulation,the compressive strength tests,axial compressive strength tests and flexural strength tests were respectively carried out for 6 different recycled coarse aggregate replacement rates and 3 ages recycled concrete specimens to analyse the influence of different recycled coarse aggregate replacement rate and age on the basic mechanical properties of recycled concrete.First of all,use the C30 grade of abandoned pavement concrete to break into the recycled coarse aggregate with certain grade,and replace the natural coarse aggregate in turn according to the ratio of 0 / 20/ 40/ 60/ 80/ 100% to study the influence of recycled coarse aggregate replacement ratio on the mechanical strength of recycled concrete at different ages of 7d~ 14d~ 28 d.A total of 162 recycled concrete specimens of 150mm*150mm*150mm,100mm*100mm*300mm and 100mm*100mm*400mm were prepared,and the cube compressive,axial and flexural strength tests were carried out on the corresponding specimens respectively,then the whole stress-strain curve of recycled concrete is obtained.According to the experimental study,with the increase of recycled coarse aggregate,cube compressive strength,axial compressive strength and flexural strength of the recycled concrete increased first and then decreased.When the replacement ratio of the recycled coarse aggregate is 40%,the mechanical properties parameters of recycled concrete reach the optimum value.In addition,based on the test data of recycled concrete mechanical properties,two important influencing factors of different recycled coarse aggregate replacement ratio and ages are considered as relevant variables,and the mathematical model of compressive strength,flexural strength,stress-strain relationship and relevant variables of recycled concrete are established by data fitting and regression analysis,from which the function expressions between compressive strength,flexural strength and replacement ratio and age of recycled aggregate for recycled concrete.Last,based on the microstructure characteristics of recycled concrete and mechanical properties of multiphase materials,an applicable constitutive model of finite element simulation is established according to the test data.On the basis of the constitutive model,the random aggregate models of recycled concrete in two and three dimensions are established,and the cube compressive strength,axial compressive strength and flexural strength are numerically simulated respectively.The equivalent stress of each model under applied load is calculated,and the change regulation of the replacement ratio of recycled coarse aggregate from 20% to 40% is considered.According to the finite element model's failure strength and crack location under ultimate load,combined with the experimental results and compared the results,it is concluded that the finite element numerical simulation is applicable to the basic mechanical properties of recycled concrete.