Sulfuric acid-resistance performances of magnesium phosphate cements: Macro-properties, mineralogy and microstructure evolutions

The acid resistance performance of magnesium phosphate cements (MPCs) are greatly concerned but poorly understood among the re-surging research efforts. Effects of sulfuric acidity (pH = 2-7) on the properties of magnesium ammonium phosphate cement (MAPC) and magnesium potassium phosphate cement (MKPC) were investigated. Results showed that MKPC was more sulfuric acid-sensitive than MAPC, and its compressive strength retention decreased to 67.5% at 28 days at pH = 2, during which process the amorphization of struviteK crystal was observed. Comparable or even higher strength was observed in MAPC cured in acids with pH higher than 2. Although the hydration degree of both MPCs increased in these liquid environments and the amorphization process was suppressed, the adverse effects introduced by the loss of NH4/K in struvite/struvite-K, change in morphology, or increase in the porosity (esp. MKPC) may outweigh the positive increase in hydration, leading to the reduction in strength.

Automated summary

The acid resistance performance of magnesium phosphate cements is of great importance and this study found that magnesium ammonium phosphate cement has better resistance to sulfuric acid than magnesium potassium phosphate cement.