Self-restraint thermal stress in early-age concrete samples and its evaluation

•Mesoscopic thermo-mechanical model for concrete sample is proposed.•Detailed parameters identification of concrete constituents is carried out.•Self-restraint thermal stress in early-age concrete sample is numerically evaluated.•Main driving factors of self-restraint thermal stress are studied. The self-restraint thermal stress caused by mismatch in thermal and mechanical behaviors of cementitious material and coarse aggregates could be a factor associated with early-age cracking in massive concrete structures, which might be even complicated when considering the mesostructure of concrete. This paper presents the application of mesoscopic model based numerical approach to trace the progression of thermo-mechanical mismatch and consequent self-restraint thermal stress development during early-age hydration in concrete. The mesostructure of concrete sample which contains aggregates, mortar and ITZ is modeled, with the material properties for each phase rationally incorporated. Thermo-mechanical behaviors of both homogeneous mortar and heterogeneous concrete samples under standard curing condition are simulated, focusing on the production mechanism of self-restraint stress. Numerical results show that the spatial-time distribution of temperature and expansion coefficient fields in concrete samples is the main origin of the self-restraint stress. The magnitude of this stress is non-negligible, which may become an influential factor to the load-bearing capacity of concrete.