Effect of magneto-rheological response on early hydration and microstructure of cement paste

Magneto-rheological control offers an innovative approach for actively regulating the rheological properties of cementitious materials. However, its influence on the early hydration processes and microstructural evolution remains inadequately understood. In this study, micron-sized Fe3O4 particles were incorporated into cement paste and subjected to an external static magnetic field. Fluidity tests were conducted to evaluate the magnetorheological responses, while XRD, SEM-EDX, and mechanical tests were used to investigate their effects on early hydration products, microstructure, and early compressive strength. The results demonstrate that the magnetic field induces a pronounced magneto-rheological response in cement paste containing magnetic particles, which persists throughout the early hydration period (within 60 minutes) and intensifies at higher water-to-cement ratios, greater particle content, and smaller Fe3O4 particle size. Neither applying a magnetic field nor incorporating magnetic particles significantly alter the types of early hydration products. Instead, the magnetic field facilitates the increasing formation of C-S-H gel network, likely by altering hydrogen bonds, while the micronsized Fe3O4 particles primarily act as fillers similar to fine aggregates. In addition, a short-term magnetic field exposure within 15 minutes enhances the 1-day compressive strength when the magnetic particle content is lower than 5 %. However, prolonged exposure or higher particle concentrations result in a mechanical anisotropy behavior, which is attributed to the movement of magnetic particles. These findings advance the understanding of magneto-rheological control on the early hydration development and mechanical properties, supporting the potential adoption of this technology in construction practices.