Microstructural evolution and texture analysis of magnesium phosphate cement

Three-dimensional quantitative image analysis from synchrotron X-ray microcomputed tomography indicated a coarsening of the microstructure of magnesium potassium phosphate cements driven by crystallization of K-struvite from the first amorphous product. Porosity and pore surface area increased because of the progressive build-up of a network of elongated/tabular crystal domains, with density higher than the amorphous. The known increase in strength with time is thought to occur thanks to the overwhelming contribution of a developing interlocked lath-shaped microstructure. Combined X-ray and neutron diffraction texture analysis indicated that at least a fraction of K-struvite nucleates at the surface of MgO grains, suggesting the intervention of more than one crystallization mechanism. The detected weak texture, compatible with a nearly random orientation of crystallites, and the isotropic pore fabric, are beneficial with respect to crack propagation.