Modulating the hydration of magnesium potassium phosphate cement through carboxyl-functionalized styrene-acrylate emulsion: Insights into kinetics and crystallization behavior

This study investigates the impact of carboxyl-functionalized styrene-acrylic (SA) emulsion as a modifying agent on the hydration process and early performance of magnesium potassium phosphate cement (MKPC), from the perspectives of hydration kinetics and crystallization behavior of hydration products. The results indicate that in the MKPC hydration system, carboxylate groups complex with magnesium ions to form stable coordination compounds, thereby reducing the availability of free magnesium ions. At the same time, the polymer adsorbs onto the cement particle surface, creating localized ion-rich regions, which causes the limited magnesium ions to be concentrated in different areas. This delays the nucleation and growth of hydration product crystals while promoting the formation of additional nucleation sites. Consequently, the second exothermic peak is enhanced, exhibiting a “delayed acceleration” phenomenon. Furthermore, it was demonstrated that hydration products form self-assembled structures on the surface of polymer particles, and the SA-K composite produced in this manner can serve as an early strength agent for MKPC. In terms of macroscopic performance, the incorporation of the polymer emulsion significantly prolonged the initial setting time of MKPC and slightly reduced early compressive strength, with a 2.2 % decrease in compressive strength at 7 days.