Mesoscale Analysis of Stress Distribution along ITZs in Recycled Concrete with Variously Shaped Aggregates under Uniaxial Compression

Abstract

Recycled aggregate concrete (RAC) has attracted tremendous attention from engineering practice and academic research throughout the world as an effective way to resolve the problems caused by the construction and demolition waste. It is generally accepted that RAC consists of five phases [(1) natural aggregate, (2) old interfacial transition zone (ITZ), (3) old hydrated cement paste, (4) new interfacial transition zone, and (5) new hydrated cement paste], among which the interfacial transition zones are of great significance to the behavior of RAC, due to their characterizations as the weakest links in the concrete mixture. It has been recognized that the shape of aggregates plays an important role in the mechanical behavior of concrete. However, there is very limited information about the shape effect of aggregates on the behavior of the ITZs in RAC. A mesoscale model of RAC is employed in the research reported in this paper to investigate the mechanical behavior of the ITZs under uniaxial compression with differently shaped aggregates. Large stress concentration factors (SCF) have been found at the morphological transitions of the aggregate. A comparison between the distributions of SCF along the ITZs indicates that the shape of aggregates has a more pronounced influence on the stress distribution along the old ITZ than that along the new ITZ, which may be due to the old hydrated cement paste attenuating the shape effect of aggregates on the new ITZ. A quadratic polynomial equation can be curve-fitted to characterize the relationship between the maximum SCF along the ITZs and the fractal dimensions of aggregates.