Experimental study on failure criterion and stress-strain constitutive equation of recycled coarse aggregate concretes under multiaxial compression

68 specimens were designed for triaxial compression test with 5 varying parameters as replacement ratio of recycled coarse aggregate, lateral confining pressure, age of concrete, sources of recycled coarse aggregate and strength grade of concrete, respectively. By observing the failure pattern of the specimens under triaxial compression, their failure mechanism can be disclosed, and the parameters of feature point such as the complete stress-strain curves of the specimens, peak stress, peak strain and elastic modulus can also be obtained. The experimental results indicate that the lateral confining pressure may significantly affect the failure pattern of recycled concrete under triaxial compression since the failure pattern may change from vertical splitting failure to oblique splitting failure and the coarse aggregates intersecting with oblique splitting failure surface are sheared off with the increase of lateral confining pressure. For the case under uniaxial compression or the case with lateral confining pressure no more than 9 MPa, the recycled concrete may fail in brittle pattern. While for the case with confining pressure no less than 12 MPa, the recycled concrete may fail in plastic pattern. Furthermore, based on the experimental study and the strength theory of ordinary concrete, the Mohr-Coulomb failure criterion, shear stress failure criterion in π plane, stress failure criteria of Rendulic plane were employed respectively to study in depth the strength criterion of recycled concrete materials from the macroscopic perspective, and discussed the stress-strain constitutive equation of the recycled concrete under multiaxial stress state. Hence, the research results should be helpful and can be referred by further researches and application of recycled concrete.