Influence of fine aggregate's morphology on mortars' rheology

Abstract

This study investigates the influence of fine aggregate's morphology on mortars' rheology. To begin with, the authors gathered a sample of aggregates with different morphology and similar size and gradation, as these are very important physical properties affecting rheology. Then, the authors quantitatively described the fine aggregate's morphology at three different scales (macroscopic, mesoscopic, and microscopic), in terms of shape, angularity, and surface texture. To characterize quantitatively those morphology properties, the parameters sphericity, roundness and fractal dimension, respectively, were selected. The results show that the morphology of fine aggregates is properly characterized by these three parameters as the characterisation techniques returned different sphericity, roundness, and fractal dimension for the aggregates in the sample and the parameters presented different trends (i.e. the parameters are independent). Moreover, the rheological behaviour of mortars prepared with the sampled aggregates show large differences, indicating that the fine aggregate's morphology has a noticeable impact on mortars' rheology. Finally, based on the discussion and analysis of the experimental results, the influence of fine aggregate's morphology can be attributed to the coupled effect of the packing density, specific surface area, and equivalent diameter of fine aggregate, and this coupled effect can be visualized using a parameter D/PFT (ratio of equivalent diameter, D, to paste film thickness, PFT). Mortar prepared with fine aggregate with a poorer morphology has a larger D/PFT value, corresponding to higher relative yield stress and relative plastic viscosity. In addition, combining previous results of the authors, it is argued that D/PFT can be used as a universal parameter to assess the rheological properties of mortars.