From settling to rheology and hydration: How fine fractions govern the behavior of cement-based suspensions

Abstract

International audienceThis study investigates the role of fine particles in governing macroscopic behaviors of suspensions, in particular, cement-based pastes. Granulometric analyses were performed on both raw and binary systems of Portland cement with limestone filler re-grinded or not (LF2, LF1), and fly ash (FA) at various substitution rates (0–100 % vol) to modify fine particle content and identify a particle size threshold. Based on granulometric analyses, a threshold of 5 μm was justified and chosen for subsequent investigation. Suspension stability was assessed using Turbiscan Lab, measuring both settling velocity and supernatant clarity. The results indicate that systems with a higher fine fraction, such as those with LF2 (97.6 %), exhibit enhanced stability, as evidenced by significantly reduced settling velocity compared to LF1 (54.4 %) that demonstrates moderate stability, and FA (34.4 %) that displays pronounced instability. Rheological measurements were performed on raw and 50 % binary systems, and the results revealed that systems with a higher fine fraction exhibit a higher storage modulus G', notably LF2 compared to LF1 and FA, and OPC-50LF2 compared to OPC-50LF1 and OPC-50FA, indicating a denser structural network. Additionally, systems with a high fine fraction displayed a lower percolation threshold confirming the enhanced ability of fine particles to form interconnected networks. Isothermal calorimetry further showed that replacing 50 % of OPC with LF2 and LF1 leads to an increase in the intensity of the main hydration peak by 58 % and 47 %, respectively, compared to pure OPC, indicating that the nucleation-precipitation effect is more pronounced when more fine particles in the system