A Combined Damage and Mesomechanics Model for Recycled Aggregate Concrete Reinforced with Steel–Polypropylene Fibers

Due to microdefects within recycled aggregates, recycled aggregate concrete (RAC) has poor mechanical properties. Researchers have found that RAC’s mechanical qualities can be enhanced by the addition of single steel or polypropylene fibers. However, the mechanical properties of RAC containing steel–polypropylene hybrid fibers (SPHFs) have been studied relatively little. In order to assess the influence of SPHFs, this paper analyzes the impact of SPHFs experimentally on the compression performance of the RAC. Additionally, using acoustic emission (AE), the damage variables of recycled aggregate concrete reinforced with steel–polypropylene fibers (SF-PF-RAC) can be quantitatively defined. Then, based on the mesomechanics approach, a constitutive model combining damage and mesomechanics is developed for predicting the mechanical properties of SF-PF-RAC under uniaxial compressive loading. The experimental results show that the bridging effect of SPHFs can greatly enhance the mechanical properties of RAC. According to the AE and experimental phenomena, the damage evolution of SF-PF-RAC under uniaxial compression can be divided into three stages: initiation of damage, stabilization of damage, and accelerated growth of damage and failure. The correctness of the model used in this paper is confirmed by contrasting the model’s predictions with those of other classical concrete theory models. Parameter inversion is also used to further validate the reasonability of the present model. Thus, it can be believed that this paper’s experimental and theoretical research on SF-PF-RAC can provide some references for the resourceful application of RAC.