Investigation of magnesium phosphate cement hydration in diluted suspension and its retardation by boric acid

Abstract Magnesium phosphate cements (MPCs) are used for rapid repair works, but they may also offer prospects for the stabilization/solidification of deleterious waste. MPCs contain calcined magnesium oxide and a water-soluble acid phosphate, such as potassium dihydrogen phosphate (KH 2 PO 4 ). The main precipitated hydrate is then K-struvite (MgKPO 4 ·6H 2 O). This work aims at giving new insight into the processes involved in its formation. Since cement hydration is very rapid, the second objective is to understand how boric acid, a common admixture for field application, retards cement hydration. A multi-stage process is evidenced in diluted suspension: MgHPO 4 ·7H 2 O likely precipitat…