Phase Field Modeling at Mesoscale of Recycled Aggregate Concrete

We devised a mesoscopic model for recycled aggregates, enabling the deduction of mechanical behavior of finite element representative volume element (RVE) size from constituent properties like aggregate and mortar. This model can be integrated into a finite element solver as the material law, computing macroscopic properties based on individual constituents. It interprets material response under stress and strain by differentiating it into elastic and viscoplastic components. The elastic response uses a compressible neo-Hookean material model, while the viscoplastic response employs a nonassociated Perzyna-type model, accounting for rate-dependent deformation. We modified the Drucker-Prager yield function to predict fracture, and phase field equations describe fracture initiation and propagation. The model was applied to study fracture propagation in recycled aggregate concrete at a mesoscopic level, illustrating how fracture originates and spreads. After model calibration and validation, a parametric study examined the impact of residual mortar on an aggregate and new mortar matrix in the stress-strain relationship. Our investigation identified the significance of mechanical properties in the overall stress-strain relationship and failure patterns of recycled aggregate concrete (RAC), notably the new mortar matrix and old mortar adhesions. The model enables the prediction of fracture behavior in RAC with complex structural heterogeneity caused by recycled aggregates.