Upscaling active rheology control to cement mortar with the intervention of an inline magnetic field

Upscaling the printing ink from cement paste to mortar level is the path people must take to apply active rheology control to smart and advanced digital fabrication, which will decrease the content of binder and reduce carbon footprint. This study investigates the rheological response of cement mortars with carbonyl iron particles (CIPs) by using penetration tests and vane tests. A customized magnetorheological test setup, making use of a pipe/nozzle-like inline magnetic intervention, was developed to modify the rheological properties of responsive mortars within a few seconds. The alignment of magneto-responsive particles and the hindrance of sand on magneto-responsive particles in the mortars were visualized and determined by scanning electron microscopy (SEM). With an inline magnetic field, the yield stress determined by the slow penetration test and the torque measured by the vane test increased by a significant factor. The magneto-responsive effect and the response speed rate of the mortar can be adjusted on demand and in time. The effect of cement-to-sand (c/s) ratios and sand gradations on the magnetorheological response of cement mortars was studied. With the increase of sand content (decrease of c/s ratio), the percent increase of yield stress and torque decreased and the magneto-response speed reduced, which indicates a reduction in response efficiency. The magneto-responsive particles could more easily move in the mortar when the particle size of sand increased. Experimental proofs of concept to apply active rheology control to a 3D printing nozzle or pumping line were conducted.