In order to better understand the failure mechanism of recycled aggregate concrete (RAC), a numerical study on modelled recycled aggregate concrete (MRAC) was conducted to investigate the plastic-damage response and crack propagation under uniaxial loading. In the numerical model, the nanoscale mechanical properties and the thickness of the interfacial transition zones (ITZs) were obtained based on advanced nanoindentation. The constitutive relationships of new and old cement mortars and corresponding ITZs were developed using plastic-damage constitutive relationships. The effects of the relative mechanical properties between new and old cement mortars on the failure pattern and stress-strain response of MRAC were investigated. After calibration and verification with the uniaxial compression test, the numerical model was found to be able to reveal the failure pattern and stress-strain curves of MRAC under uniaxial tension. The results showed that microcracks usually first appear around the weak new and old ITZs, and then propagate into the new and old cement mortars. With an increase in the relative strength between new and old cement mortars, the microcrack initiation locations gradually shifted from the new ITZs to the old ITZs. Therefore, the numerical results can provide insight into the modification of RAC using mix design optimisation and ITZ enhancement.