Active rheology control of cementitious materials: New insights from magneto-responsive aggregates

This study aims to achieve active rheology control of cementitious materials from the new view of magneto-responsive aggregates. It provides a sound experimental validation, qualitative analysis and quantitative characterization of magnetorheological response and mechanism of cementitious materials containing responsive aggregates under a nozzle/pipe-like (inline) external magnetic field. Specially, the aggregate shape indicators, rheological responses and micro-/meso- structures are described. The physical, chemical and geometrical features of aggregates were determined by X-ray diffraction analysis (XRD), vibrating sample magnetometer (VSM), loose packing fraction, optical microscopy and X-ray computed tomography (CT). The slow penetration test and vane test were conducted to measure the structural build-up of fresh samples with and without an inline magnetic intervention by using a rheometer-based customized test setup. The spatial distribution of magneto-responsive aggregates was determined by employing X-ray CT. The internal skeletal contact properties of magneto-responsive aggregates including cluster orientation, cluster aspect ratio, cluster elongation, contact point number, contact length and contact area were characterized quantitatively from the 3D image. A newly developed magneto-responsive cement mortar which can adjust rheological properties in time and on demand was achieved. The alignments of magneto-responsive aggregates along the magnetic induction lines were visualized. The orientation of magneto-responsive aggregate clusters showed concentrated distribution. With the decrease of the cement-to-aggregate ratio and increase in the size of magneto-responsive aggregates, the field-induced yield stress and torque increased significantly, which also influenced the contact properties of magneto-responsive aggregates. These results are beneficial for the application of active rheology control of magneto-responsive cementitious materials.