Effect of temperature curing on properties and hydration of wollastonite blended magnesium potassium phosphate cements

K-struvite, the main hydrate of magnesium potassium phosphate (MKP) cements, dehydrates at similar to 50 degrees C, thus elevated temperatures at service conditions could affect cement properties and durability. In this study, properties and hydration of MKP cement without and with wollastonite were investigated at 20 and 50 degrees C. In hydrated pure MKP cement K-struvite decomposes progressively over time to MgKPO4 center dot H2O at 50 degrees C, which leads to a strong reduction of solid volume and severe strength loss. The presence of wollastonite significantly slows down the decomposition rate of K-struvite, which is still observed after 393 days at 50 degrees C. K-struvite together with amorphous hydroxyapatite, M-(C)-S-H and CaK3H(PO4)(2) from the wollastonite reaction result in a cement with good short and long-term strength at both 20 and 50 degrees C.

Automated summary

The study shows that hydration of MKP cement at 50 degrees Celsius leads to the gradual decomposition of K-struvite, but the addition of wollastonite can significantly slow down this process, maintaining the strength of the cement. The products formed from the reaction with wollastonite contribute to the good strength of the cement at both 20 and 50 degrees Celsius.