Effect of temperature curing on properties and hydration of wollastonite blended magnesium potassium phosphate cements
Biwan Xu, Frank Winnefeld, Barbara Lothenbach
Abstract
K-struvite, the main hydrate of magnesium potassium phosphate (MKP) cements, dehydrates at ~50 °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 °C. In hydrated pure MKP cement K-struvite decomposes progressively over time to MgKPO4·H2O at 50 °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 °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 °C.