Effect of Magnetorheological additives on the buildability of 3D concrete printing

Effect of Magnetorheological additives on the buildability of 3D concrete printing

This study investigates the effect of magneto-rheological additives in 3D concrete printing as a stimuli-responsive technique for buildability enhancement. The carbonyl iron powder (CIP) was used as the magnetorheological additive. Two distinct magnetic activation strategies of print-bed magnetisation and print-head magnetisation were considered. The fresh properties including static yield strength development and viscosity representing the buildability and pumpability characteristics of magnetorheological cement mortar (MRC) mixtures were assessed for both strategies. Besides, the compressive strength and volume of permeable voids (VPV) were studied to assess the effect of CIP on the hardened properties of MRC mixtures. It was found that the addition of CIP had a significant enhancement in the static yield strength of fresh MRC mixtures when the magnetic field is continuously present (i.e., print-bed magnetisation). However, short-duration exposure to the magnetic field (i.e., print-head magnetisation) resulted in a slight improvement in static yield strength, revealing that the residual effect of MRC mixtures is insignificant. For instance, the MRC mixture with a CIP dosage of 10% by weight exhibited a static yield strength of 15 kPa at 20 min when subjected to continuous magnetisation, whereas the same mixture showed a static yield strength of 5 kPa at 20 min for short-duration magnetisation (the exposure time of 60 s). The hardened properties of CIP incorporated MRC mixtures showed the enhancement in compressive strength and reduction in volume of permeable voids for CIP dosage up to 5% with further increase in CIP dosage lead to strength reductions.