From static to continuous shear: Unraveling the time-dependent evolution of cement paste rheology

The rheological properties of cement paste evolve significantly over time, exhibiting distinct behaviors under static and continuous shear, thus critically influent modern construction processes. However, the mechanisms governing the time-dependent rheology under continuous shear remain unclear. This study investigates the dynamic evolution of fluidity and rheological parameters of cement pastes under shear conditions, aiming to reveal the intrinsic coupling among microstructural rebuild-up, colloidal interaction, and hydration kinetics. Mini-slump flow tests and rheological tests, combined with small amplitude oscillatory shear (SAOS) tests, characterized the evolution of fluidity, yield stress, and structural build-up under static and continuous shear conditions. Meanwhile, ionic concentration analysis, XRD, TG/DTG, and SEM were employed to track the hydration phase and microstructure variation. The results show that continuous shear markedly suppresses the structural build-up and delays the increase in yield stress and viscosity, maintaining flow stability over time. SAOS tests demonstrate that the structural evolution under shear is governed by the competition between dispersion and association: van der Waals forces dominate early flocculation, while sustained shear weakens their effect and enhances ion correlation interactions, resulting in a dynamic equilibrium of the microstructure. Hydration analysis further reveals that shear promotes ion dissolution but delays the formation of early hydration products such as AFt and C-S-H, which explains the retarded rheological stiffening. This study establishes a coherent mechanistic framework linking rheological time-dependency, colloidal interaction, and hydration under continuous shear. The findings offer new insights into the rheological design of cementitious materials for shear-dominated processes.