Triaxial mechanical behaviour and constitutive response of rubberised concrete materials

This article conducts experimental studies on the stress-strain response of concrete materials incorporating recycled tyre rubber particles, namely rubberised concrete (RuC), under triaxial compressive loads. A series of experimental investigations are carried out on a multifunctional triaxial testing device to examine the effects of rubber replacement ratios and active lateral confinement loads on the mechanical properties of RuC. Four confinement ratios (ratio of lateral stress to uniaxial strength) of 0 %, 10 %, 20 %, and 30 % and five volume rubber replacement rates of 0 %, 10 %, 20 %, 30 %, and 40 % are adopted for observing changes in the stress-strain response of RuC under triaxial compared to uniaxial compression. The experimental results indicate that the rubber content is a key parameter related to the mechanical properties of the mixes which significantly influences compressive strength as well as deformability of RuC under both uniaxial and triaxial loads. For example, the triaxial compressive strength of R40 decreased to 20.4 % of R0 as the confinement ratio was 30 %, and the peak strain increased from 0.43 to 0.80 of R0. In addition, the increase of rubber content significantly improves the energy dissipation ability of RuC under different levels of confining pressures. It has been found that the softening branches of the stress-strain behaviour of RuC are clearly influenced by both the rubber contents and confinement ratios. Based on experimental results, mathematical expressions describing the relationship between the crushing strain of RuC and maximum deviatoric stress considering the effects of rubber contents and confinement ratios are proposed. An analytical model is also proposed for the detailed assessment of the full constitutive response of RuC under various confinement ratios. Validations of the proposed expressions against the experimental results show that the constitutive model provide reliable prediction of the complete stress-strain response of RuC.