Experimental Study On Mechanical Properties Of Recycled Concrete From Abandoned Brick Construction Waste

In order to reduce the adverse impact of construction waste and natural stone resources on the ecological environment,recycled concrete technology has emerged as the times require.At present,the sources of recycled coarse aggregates in reported studies of recycled concrete are generally waste concrete.Considering the diversity and complexity of the composition of construction waste in China,and the different types of recycled coarse aggregates have different effects on various aspects of concrete performance,In this paper,different types of recycled concrete containing bricks are made by using recycled brick aggregate construction waste generated from dismantling brick-concrete structures as the recycled coarse aggregate.The two types of recycled concrete containing bricks are produced by using the substitution rate and the diameter of the recycled coarse aggregate as parameters.The influence of each parameter on the compressive strength,split tensile strength,fracture performance and damage performance of uniaxial compression of recycled concrete.The main work and research results of the paper are as follows:(1)The basic physical properties of recycled coarse aggregate with bricks and natural coarse aggregate were tested.The water absorption,crushing index,apparent density and loose accumulation of recycled coarse aggregate with bricks and natural coarse aggregate were analyzed and studied.(2)The compressive strength test,split tensile strength test and ultrasonic testing test under different stress conditions were performed on each group of brick-containing recycled concrete cube specimens.The results show that with the increase of the replacement rate of recycled coarse aggregate containing bricks,the compressive strength and splitting tensile strength of recycled concrete with bricks gradually decrease,the ultrasonic wave velocity in the state of zero stress gradually decreases,and the concrete The damage resistance gradually decreases;when the replacement rate of the recycled coarse aggregate containing bricks is constant,the brick-grained recycled concrete made with a smaller particle size replacement method has relatively large compressive strength,split tensile strength,and initial strength.The ultrasonic wave velocity and the damage degree under each stress state are relatively small;the function relationship formula of the damage degree of the recycled concrete and the compressivestrength and compressive stress coefficient under the condition of uniaxial compression is established.(3)Based on the double-K fracture model and virtual crack model of concrete,the double-K fracture toughness,fracture energy and ductility index of each group of recycled concrete containing bricks were obtained through experimental research on the fracture performance of three-point bending beams.The results show that the double-K fracture toughness,fracture energy,and ductility index of brick-containing recycled concrete gradually decrease as the replacement rate of brick-containing recycled coarse aggregate increases.The brick-grained recycled concrete produced by the substitution method has relatively large instability toughness,fracture energy and ductility index,and the brick-grained recycled concrete produced by the substitution method with large particle size has large crack initiation toughness.(4)Using the difference box algorithm,the fractal dimensions of the fracture surface of each group of brick-containing recycled concrete specimens were extracted by Matlab software.The relationship between the fracture energy and fractal dimension when considering the substitution rate of recycled coarse aggregate containing bricks and the relationship between the fracture energy and fractal dimension of the two test groups of recycled coarse aggregate substitution rate and substituted particle size are established formula.