Improvement in the water resistance of MAPC coatings as a function of NaCl concentration

This study focused on the waterproofing effectiveness of magnesium ammonium phosphate cement (MAPC) coatings at different sodium chloride (NaCl) concentrations (0, 3, 5 and 7%). It included qualitative analyses and quantitative tests of the effect of sodium chloride on three characteristics: tensile strength, water absorption rate and thickness of coatings. The influence of the changes in the structure and composition of MAPC coatings on their water resistance performance was also analyzed. It was found that 3% sodium chloride concentration could remarkably improve the waterproofing effect of MAPC coatings. Another finding showed that tensile strength, water absorption rate and coating thickness increased at the very beginning but these decreased as the sodium chloride content increased. Moreover, compared with other concentrations, the structure and composition of MAPC coatings containing 3% sodium chloride were found to be stable in water. The coatings were bonded to the concrete more tightly, which resulted in a more compact structure and thus a higher water resistance effect.