Phase and microstructure evolution of the hydration products of magnesium phosphate cements under sulfuric acid environments

Magnesium phosphate cement is a good canditate of repairing material served under harsh environments and its acid resistivity has drawn a lot of interest, but rare detailed research on the evolution of its physiochemical features has been reported. In this work, the impacts of sulfuric acid solution (pH = 2 – 7) on the hydration products of magnesium potassium phosphate cement and magnesium ammonium phosphate cement. Results showed that the main hydration products, struvite/struvite–K, experienced partial corrosion in the absence of the sulfuric acid solution replacement. The phase transition of struvite–K is clearly visible, leading to the formation of the new crystalline hydration product Mg₃(PO₄)₂•22 H₂O. The initial blossoms cluster microstructure transformed into a diffused dispersion that resembled a plate. When the solution was replaced, struvite/struvite–K underwent significant corrosion and even complete decomposition in more acidic (pH = 2, 3) solutions.