A comparison of magneto-responsive particles and testing protocols for active rheology control of cementitious materials

Magneto-responsive cementitious materials with magnetic interventions enable on-demand and real-time adjustment of rheology. This research aims to elaborate the early-stage magneto response of cement pastes using different types of Fe3O4 particles and carbonyl iron particles. A series of methods to evaluate the magnetorheological response of cementitious materials were established. The magneto-responsive cement pastes were tested by shear test and small amplitude oscillatory shear test at constant and time-varying magnetic fields. The increase of static yield stress and storage modulus after applying a magnetic field was a time-dependent process, while the decrease of static yield stress and storage modulus was an instant process at the moment of removing magnetic fields. Such a procedure can be reversibly controlled in real time. The cement pastes containing different magneto-responsive particles showed significant difference in the onset of flow and structural build-up. With the intervention of a magnetic field, the static yield stress and storage modulus of mixtures with carbonyl iron particles were able to increase with one order of magnitude. Compared with the particle size distribution and particle morphology, the magnetic parameters of magneto-responsive particles dominated the magnetorheological properties of cementitious materials. Shear tests were found the most effective to evaluate the magneto response of cement pastes with the intervention of a magnetic field.