Revealing time-dependent dominant factors regulating rheological property in cement-slag pastes — Based on grey relational analysis

To investigate the effect of slag fineness on cement paste rheology, this study prepared a series of cement-slag pastes with varying physical characteristics using slags with different fineness. Grey relational analysis was applied, with physical parameters including median particle size (D50) of the slag, total specific surface area (TSSA), distribution modulus ( n A ), slag content, and water film thickness (WFT) as comparative sequences. The degree of correlation between these comparative sequences and the reference sequences (rheological parameters at 15 min and 90 min reaction times) was calculated. The results indicate that in binary pastes, at a fixed slag content, a larger specific surface area (SSA) of slag gradually increases the yield stress while reducing plastic viscosity. Compared with the plain cement paste, a higher SSA of the incorporated slag leads to smaller differences in both yield stress and plastic viscosity. However, the plastic viscosity is more significantly influenced by time. Meanwhile, the dominant factors influencing rheological properties exhibited clear time-dependent variations. In the fresh stage (15 min), yield stress was primarily influenced by the TSSA, with a high correlation degree (Ri=0.84), while plastic viscosity was mainly controlled by n A . As the paste reaction progressed, the controlling effect of TSSA further strengthened (Ri=0.90) and synergistically dominated the yield stress alongside n A . Simultaneously, the correlation degree of n A , which governs plastic viscosity, also increased (Ri=0.87). Additionally, variations in slag content had a very limited effect on both plastic viscosity and yield stress. However, thixotropic properties consistently showed moderate correlations with multiple factors. This study ultimately established a model of the synergistic effects of physical factors on the rheological properties of the cement-slag system, illustrating the transition from individual dominance of physical characteristics to synergistic interactions as the paste reaction advanced. • Rheological dominance shifts from single physical factors to their synergy during hydration. • A novel physical model integrates particle traits and water film thickness to predict rheology. • Grey relational analysis quantifies multi-factor effects, confirming thixotropy lacks a single dominant parameter.