Effects of Interfacial Characteristics of Recycled Aggregates on the Performance of Recycled Concrete

Abstract

This study examines how the quality and content of residual old mortar in recycled coarse aggregates affect the compressive strength and resistance to chloride ion permeability of recycled concrete. Nine types of recycled coarse aggregates with different old mortar contents and qualities were chosen to prepare 27 groups of recycled concrete specimens, which were tested for compressive strength and chloride ion permeability. The results demonstrate that a lower water-cement ratio in the parent concrete improves the compactness of the old mortar, significantly increasing the compressive strength of recycled concrete, while its impact on chloride ion permeability is minimal. Additionally, a lower paste-aggregate ratio in the parent concrete reduces the old mortar content, which influences the number of interfacial transition zones (ITZs). An increase in the number of ITZs substantially weakens the concrete’s compressive strength and durability. Based on the experimental data, predictive equations incorporating ITZ parameters and water-cement ratio were developed to estimate the performance of recycled concrete. Comparative analysis indicated that linear models fit well with literature data and shows high accuracy.