Influence of Aggregate Particle Size Distribution on Mixing Behavior and Rheological Properties of Low-Binder Concrete

摘要

Particle Size Distribution (PSD) has impact on the workability of concretes because it affects the particle packing and particle mobility during flow. In continuous concrete production, keeping always the same PSD is not possible. So, it is important to understand how this variability affects concrete properties. The research described in this paper evaluated a more sustainable low-binder concrete, with focus on particle size variability of the aggregates. Applying particle packing and dispersion concepts, rheological control, use of limestone fillers and appropriate choice of material, a reference concrete with low binder consumption (3.7 kg/m~3/MPa) was developed. On this reference concrete, PSD variations were applied: a coarser and a finer version for each aggregate was tested and two levels of fines content were also evaluated. Mixing behavior and rheological properties were determined by a concrete mixing rheometer (Pheso Poli-USP) with planetary configuration. An acceptance criterion was established based on mixing torque and all concrete outside the limits had their water content adjusted until they met the specifications. After that, mechanical strength was evaluated at 28 days of age. The obtained results indicate that PSD variations affected both the mixing and flow of concrete. Especially higher fines content and presence of a finer natural sand increased the torque levels during the mixing process and shear cycles and lead to higher mixing power demand. The water correction, adopted to overcome the rheological changes, affected hardened state properties (up to 10% on compressive strength). As these findings are specific to the analyzed concrete and considered PSD variations, this research aimed to explain more generally the influence of the several variables. The surface area of the granular material, solids concentrations and mean distance between the fine and coarse particles are some quantitative parameters useful for predicting rheological aspects of concrete compositions.