Effect of zinc oxide on synthesis of magnesium potassium phosphate cement

Magnesium potassium phosphate cements (MKPCs) have been developed for the rapid repair of civil engineering structures and the solidification of hazardous waste. However, the rapid curing and high heat of hydration of MKPCs pose challenges in bulk production. To address this problem, the use of zinc oxide as a novel retarder for MKPC synthesis was investigated. Compared with conventional retarders like boric acid, zinc oxide was found to delay the initial hydration of MKPCs significantly, although its effect diminishes over time. The addition of zinc oxide accelerated the dehydration of MgHPO4.7H2O to MgHPO4.3H2O. It is likely that Zn2+ ions inhibit the dissolution of magnesium oxide by surface adsorption or dehydration of Mg(H2O)62+. Using zinc oxide as a retarder provides sufficient mixing time, making it advantageous for practical applications where a controlled setting time is crucial.