A New Method for Predicting the Rheological Properties of Recycled Aggregate Concrete with a Multiscale Two-Phase Perspective

This study aims to address the issues of rheological design and prediction of recycled aggregate concrete (RAC), given the complex particle characteristics of recycled aggregates (RA). To this end, the present study systematically investigates the rheological behavior of concrete incorporating RA with varying particle sizes, shapes, and volume fractions, where relationships between RA’s particle morphology, packing behavior, and rheology were established. By quantifying paste film thickness, a multiscale two-phase prediction method was developed, which integrates the morphological parameters of aggregates and the rheological properties of suspension fluids. The findings reveal that, in terms of morphology, both recycled coarse aggregate (RCA) and recycled fine aggregate (RFA) exhibit rough surface features and irregular shapes. Beyond particle size distribution, RA’s morphology significantly affects the corresponding particle packing behavior. The rheological models provide reliable estimates of the maximum packing fraction with a R2>0.96, which aligns closely with the measured dense packing fraction. In comparison with the experimental data of static and dynamic yield stress and plastic viscosity, the deviation of the calculation results by the proposed multiscale two-phasic model is mostly within 20%. Therefore, this method holds substantial promise for facilitating the large-scale application of RAC.