Analysis of Damage Mechanisms and Evolution in Recycled Aggregate Concrete Considering the Effects of Water–Cement Ratio and Pore Water

To study the effect of water–cement (w/c) ratio and pore water on the mesomechanical properties of recycled aggregate concrete (RAC), a computational model of RAC that takes into account various w/c ratios (0.3, 0.36, 0.4, 0.41, 0.49, 0.5, 0.6, 0.7) and porosities (3%, 6%, 8%, 10%, 12%) is established using the Monte Carlo approach. The base face element method (BFEM), an innovative finite element approach derived from complementary energy principle, is applied to calculate the stress and flexibility matrix of each element in a precise description while avoiding the Gauss calculus. The effects of w/c ratio and pore water on stress–strain curves, compressive strength, tensile strength, elastic modulus, and damage modes are investigated. The simulation results show that the compressive strength, tensile strength, and compressive modulus of elasticity gradually decreased while the w/c ratio increased from 0.3 to 0.7. The extended path of damage cracks gradually shifts from the old interfacial transition zone (ITZ) and interior of the old cement mortar to the new ITZ and new cement mortar between the localized cracks. Damage cracks are mainly found in the new cement mortar surrounding the dense area of aggregates. Pore water must be taken into account in the analysis because it significantly affects the tensile mechanical properties of RAC.