Rheological properties of mortar with recycled fine aggregate: From the perspective of particle packing

This study has assessed the rheological properties of mortar incorporating recycled fine aggregate (RFA) particles, focusing on the impact of the aggregates' volume fraction, size, and morphology. Particle morphology indicators of RFA were determined through comprehensive image analysis, while the packing densities under varying compaction energies were examined. The rheological properties of mortar were assessed via stress growth test and flow curve test. The findings indicates that fine-grained RFA with low sphericity, high elongation, high fractal dimension, and high specific surface area exhibits lower packing densities irrespective of compaction energy or moisture conditions. In terms of mortar's rheological properties, the relative plastic viscosity is positively associated with RFA's volume fraction and strongly correlated with the morphological indicators. Fitting results from Quemada model and Robinson model both demonstrates that shear action enhances the packing density of the particle system. From a biphase perspective considering paste-aggregate or water-solid interactions, it is observed that irregular shape and rough surface characteristics of RFA lead to a reduction of the packing density within the aggregate or solid system, which ultimately determines macroscopic flow ability by influencing free paste or water volume in the mixture. Therefore, the influence of aggregate characteristics on the rheological properties of mortar can be precisely elucidated through the particle packing behavior.