Low Carbon Footprint Magnesium Phosphate Cement for 3D Concrete Printing

Digital 3D printing has become a viable technique in construction that can increase productivity while reducing costs. Substitution of conventional cementitious materials by innovative cement matrices, containing natural raw materials and industrial wastes, might help to reduce environmental issues associated to carbon emissions. Magnesium phosphate cements are rapid setting binders with low water content and capacity to include large amounts of industrial by-products in their formulation. Rheological properties, setting time and mechanical strength displayed by magnesium phosphate cement formulation are reported in this study with the objective to limit the conditions related to pumping, extrudability and deposition, which are key functional parameters for 3D printing by material extrusion technology. An optimized magnesium potassium phosphate cement formulation was proposed, prior to a 3D printing test, containing a blend of high- and low-grade MgO, a magnesium to phosphate molar ratio equal to 4, the minimum stoichiometric water content to produce K-struvite, a content of retarder equal to 3wt.% and a filler to binder ratio equal to 0.5.