Development of 3D-printed magnesium silicate hydrate cement mixes involving metakaolin as a substitute for silica source

The printability of MgO-SiO2 cement pastes involving the use of microsilica (MS) and metakaolin (MK) as a SiO2 source was thoroughly investigated. Fresh properties, including rheology and early-age strength, mechanical properties and microstructures of pastes incorporating different contents of MK were presented and analyzed. Amongst samples studied, those containing 5% MK as a substitute for MS exhibited the highest static yield stress, and fastest re-flocculation and structuration rates, resulting in the best buildability. Although the inclusion of 10% MK resulted in enhanced paste strength at 7 and 28 days, increased MK content impeded paste printability due to diminished formation of hydrate phases. Use of 5% MK led to higher M-S-H generation compared to other samples at 28 days, contributing to subsequent strength development. Results demonstrated that optimisation of the MK content in MgO-SiO2 pastes can yield satisfactory mechanical strengths without compromising printability.