Understanding the rheological behavior of reactive magnesia-metakaolin system in the context of digital construction

Application of 3D printing in building projects can enhance construction efficiency and productivity. Rheological properties play a key role in defining the suitability of different cement-based mixes for digital construction. In this study, the rheological behavior of the MgO-SiO2 system involving metakaolin (MK) as the silica source was thoroughly investigated. Mixes with two different MgO/MK ratios (1 and 1.5) were prepared and evaluated for their hydration process, solid phase analysis, and dispersion stability of suspension particles by utilizing isothermal calorimetry, zeta potential, XRD, and TG-DTG analyses. Results revealed that the median differential viscosity (μdiff), dynamic yield stress (τd), and static yield stress (τs) of M50-MK50 were considerably greater than those of M60-MK40. The increase of τs over time adhered to the linear structuration model within 60 min of hydration. The small amplitude oscillatory shear (SAOS) test findings indicated that M50-MK50 paste had a larger storage modulus. Although the printed structure of M50-MK50 closely approximated the intended dimensions of the design, notable instability was evident in the first and third layers from bottom to top. Microscopic analysis revealed that the formation of a modest number of hydration products in the early stage, the tendency of the system to agglomerate due to the smaller particle size of MK, and the irregular morphology of MK are significant variables influencing the rheological behavior of the MgO-MK mixes.