Understanding variability in recycled aggregate concrete mechanical properties through numerical simulation and statistical evaluation

This paper investigates the effects of adhered mortar content on the mechanical properties of recycled aggregate concrete (RAC) systems using two-dimensional finite element analysis of RAC specimens subjected to uniaxial compression. Sensitivity and statistical analyses of RAC systems were conducted to explore how individual material stiffnesses (aggregate, mortar matrix, adhered mortar, new Interfacial Transition Zone (ITZ), and old ITZ) and adhered mortar contents (2, 10, 20 and 50%) influence RAC mechanical performance. In total, 128 simulation results were performed to understand variability in stress development, damage progression, compressive strength, and elastic modulus of RAC systems. Statistical inferences on the effects of variability in material stiffness and adhered mortar content were made based on frequency distributions, probability density functions, Pareto charts, main effects plots, and bivariate contour plots. Numerical results showed that compressive strength and elastic modulus decreased with increasing adhered mortar contents, while the strain corresponding to compressive softening increased with adhered mortar contents. Statistical results showed that compressive strength was most significantly influenced by aggregate stiffness and mortar matrix stiffness. Strain localizations were observed near the aggregate boundaries due to large material stiffness discontinuities in the RAC meso-level structure. RAC elastic modulus and ultimate compressive strain were mainly governed by the stiffness of the mortar matrix. Based on the numerical results, bivariate contour plots were developed to understand how variations in material stiffness and adhered mortar content influence the strength and stiffness of RAC systems.