Active stiffening control by magnetically induced blocking in confined flow of fly ash pastes

Formwork leakage has become one of the important challenges of modern construction parallel to the increase in use of self-compacting cementitious materials. Excessive formwork pressure coupled with the highly flowable nature of these materials could lead to increased formwork leakage. This paper introduces a magnetic field-based active stiffening control methodology that could be beneficial for reducing formwork leakage during casting. As a demonstration of formwork leakage, pressure-driven flow through a narrow slit was investigated on magnetisable pastes containing 40% fly ash. The active stiffening control was incorporated by applying an external magnetic field at the outflow. The mass of the outflowing material was continuously recorded, and the flow rate and final net mass loss evaluated. Experimental results showed reduction in flow rate after applying the external magnetic field due to the agglomeration of magnetisable particles contained in the fly ash at the outflow region. It is concluded that the confined flow of pastes containing magnetisable particles can be actively controlled by the application of a magnetic field. The effectiveness of the introduced methodology is mainly dependent on the introduced magnetic field strength, paste viscosity, flow width to magnetisable particle size ratio and pressure level.