Verification of concrete nonlinear creep mechanism based on meso-damage mechanics

In order to study the nonlinear creep mechanism of concrete materials, predict and evaluate the safety of the structure, uniaxial nonlinear creep tests of concrete specimens under different ages and stress-strength ratios (σ/f_c) were carried out. Based on the discrete element theory (DEM), a concrete three-phase numerical simulation model is established, which considers the real aggregate shape and the strength difference of each phase material. The study found that the nonlinear creep duration of the early-age concrete specimens increases exponentially with age, and decreases exponentially with the increase of stress-strength ratio. Age has the greatest influence on total deformation of concrete nonlinear creep. The quantitative relationship between creep characteristics (duration, total deformation) and control variables (age, stress-strength ratio) is established. The numerical simulation model simulates the uniaxial nonlinear creep process of the concrete specimen. Compared with the measured data, it is found that the creep curve is in good agreement. At the same time, the overall trend of the measured damage value defined by the wave velocity and the damage simulation value defined by the number of cracks is in good agreement, which objectively reflects the general law of damage and crack development in the nonlinear creep process. Through the analysis of the failure mode and fabric diagram of the concrete specimen, the microcracks first occurred on the interface. At the same time, the cement gel in the cement mortar undergoes viscous flow, the stress is redistributed, and the microcracks continue to produce, expand, and connect, which ultimately leads to the complete failure of the specimen. The quantitative relationship and numerical simulation model proposed in this paper can be applied to the creep prediction and safety calculation of components or buildings under the condition of high stress-strength ratio, and has a good engineering application prospect. © 2021 Elsevier Ltd.