Influence of rheometer configuration and aggregate size on the rheological characterization of cement-based materials

Rheological characterization of cement-based materials is influenced by artifacts arising from material heterogeneity and rheometer geometry. This article investigates the compatibility of three different concrete mixes – self-compacting concrete (SCC), vibrated pumpable concrete (PC), and mortar (M) with constituent proportions similar to that of a 3D-printable concrete – with three rheometer configurations. The investigated rheometer geometries include a slotted-vane impeller with a ribbed-walled container (SV), and vane (V) and attritor impellers (AP) used with a smooth-walled container. Flow curve tests and slump/spread measurements were performed with time. Stress growth tests (SGT) are performed to study the evolution of the static yield stress with time. A signal-based post-processing approach, termed Signal Window (SW) analysis, is proposed to evaluate the noise-to-signal (N/S) ratio and assess the quality of stress growth data. The results indicate that stress growth measurements obtained for mixes containing coarse aggregates exhibit increased noise and scatter, whereas lower N/S values were consistently associated with smoother stress evolution for finer mortar systems. Among the investigated configurations, slotted-vane geometry exhibited lower N/S ratios (typically ∼0.13–0.20), compared to vane and attritor geometries (∼0.28–0.60), indicating improved signal stability under the tested conditions. The study highlights the importance of explicitly assessing signal quality when interpreting concrete rheological data and demonstrates the utility of SW analysis as a diagnostic tool for evaluating the compatibility between rheometer configuration and concrete type.