An Experimental And Numerical Study On Stress-Strain Relationship Of Recycled Concrete Under Uniaxial Loading

As a kind of environmental green construction material, recycled concrete has attracted more and more researchers. They have carried out series of experiments and some conclusions have been reached. However, because of the complexity of recycled coarse aggregates, conclusions made by different researchers are usually not very accordant, even opposite sometimes. To remove effects of experimental conditions a lattice model has been formed to consider how the compositions influence the characteristics of recycled concrete.This paper collects almost all the SEM (Scanning Electron Microscope) experimental results in this field, analyzes the microstructure and ITZ (Interfacial Transition Zone) of recycled concrete. Some conclusions can be made that recycled concrete got a looser ITZ than normal concrete, but the width of micro-cracks in normal concrete ITZ is larger than recycled concrete, and the width of new ITZ in recycled concrete is larger than normal concrete. Where will the failure surface of recycled concrete take place depends on the properties of recycled coarse aggregates and the mix proportion of new mortar. When waste concrete got a higher strength and has little damage, recycled concrete inclined to damage along the new ITZ, and in the reverse situation recycled concrete will damage along the old ITZ.An experiment has been carried out to consider how recycled coarse aggregates affect the stress-strain curves. Two kinds of waste concrete, C20 and C50, are crushed and mixed at different ratios to simulate recycled coarse aggregates from different origins. Prisms (100×100×300mm~3) are cast under the same mix proportion and compressed under an electro-hydraulic servo test machine to obtain the complete stress-strain curves. Considering the stress-strain curves, it can be found that when recycled aggregates from different origins are mixed, the diversity of stress-strain curves under uniaxial compression will be increased. Meanwhile, the axial compressive strength will be decreased, and the elastic modulus will be controlled by the aggregate whose original elastic modulus of waste concrete is lower. Based on lattice model theory and microstructure of recycled concrete, a recycled concrete lattice model has been formed, and a program has been designed in Fortran to calculate the stress-strain curve. When comparing calculated curves with experimental results, it can be concluded that this model could reflect the damage process of recycled concrete, and on the premise of selecting appropriate parameters, recycled concrete lattice model can calculate a proper stress-strain curve.