A novel modelling approach for realistically-wrapped state recycled aggregates and its application in meso-scale tensile behaviour simulation of recycled concrete

Most of the existing Finite Element (FE) simulations on the mechanical behaviour of Recycled Aggregate Concrete (RAC) generally simplified the Recycled Aggregates (RAs) as simple shapes (e.g., circular / elliptical and polygonal), with residual mortar created by proportional scaling or segmentation of these shapes, which is not consistent with the real situation. Hence, this study proposed an irregular shapes overlay method and a placement algorithm to randomly generate the real-shaped RAs and build the RAC's mesoscale geometric model. Then, RAC's mesoscale FE model was established based on the cohesive zone model and got calibrated. The effects of various key parameters (i.e., the RAs substitution percentage, the residual mortar content of substituted RAs and the relative strength of residual to new mortar) on the RAC's tensile behaviour were studied. The proposed framework can effectively generate RAC's mesoscale geometric models with various RAs substitution percentages and residual mortar contents. Embedding zero- thickness interface elements between all solid elements can perfectly simulate the RAC's crack development under tensile loading, offering more realistic cracking paths compared to RAC with simple shape RAs. For the case of new mortar strength larger than the residual one, the tensile strengths of RAC decrease as the RAs substitution percentage and residual mortar content, with a reduction of up to 15%. Otherwise, the tensile strengths show no significant decrease.