Laboratory test and meso-scale discrete element modelling on creep behaviors of concrete

In this work, a series of concrete creep tests with different stress conditions were carried out by laboratory tests and the discrete element method (DEM). The instantaneous strain, creep strain, creep rate, as well as creep nonlinearity ratio were obtained by laboratory tests. Meanwhile, a DEM micromechanical model, including coarse aggregate with actual geometry, homogenized mortar, and interfacial transition zone (ITZ), was established and the validity of numerical results was verified by laboratory tests. On this basis, the mesostructure characteristics (i.e., contact force and force chain) were obtained by DEM micromechanical-based analysis. The results show that the creep strain increases with the increase of stress level and with the extension of load holding time, and the creep develops rapidly within 60 days and slowly after 60 days. As the applied stress level increases, the nonlinearity of creep strain becomes more obvious, all specimens achieve a stable nonlinear ratio after about 20 days. Meanwhile, the contact force in mortar and ITZ all tend to increase with the increase of stress level, resulting from the viscoelastic slippage in burger contact. The average contact force of ITZ is larger than that of mortar, and a difference of about 20% can be observed. The peak probability density of mortar occurs at fi/f¯ = 0.6–0.8, while that of ITZ occurs approximately at fi/f¯ = 0.5. By comparison with other models, the improved nonlinear viscoelastic-plastic creep model can well predict the creep behavior.