Microscopic simulation of thermo-mechanical behaviors in recycled concrete under freeze-thaw action

This work proposes a thermal-hydro-mechanical coupling model to simulate pore water crystallization and melting processes in recycled concrete. A random polygonal microstructure of recycled concrete was established, in which aggregates, new mortar, old mortar, new aggregate-new mortar interface transition zone (ITZ1), old aggregate-old mortar interface transition zone (ITZ2), and new mortar-old mortar interface transition zone (ITZ3) were clearly expressed. The correctness of the proposed model was verified by its comparison with available experimental data obtained in the literature. Micro-finite element simulations were conducted to evaluate the effects of new mortar permeability, old mortar water cement ratio, aggregate grading, recycled aggregate substitution rate, aggregate volume fraction, and temperature difference on the freeze-thaw behavior of concrete. The results indicated that the permeability of mortar, aggregate grading, aggregate volume fraction, and recycled aggregate substitution rate significantly impacted the freeze-thaw characteristics of concrete. In contrast, the influence of the water-cement ratio of old mortar on the freeze-thaw behavior of concrete was relatively low. In addition, the impact of environmental temperature differences on the freeze-thaw behavior of concrete needs to be considered.