Reaction mechanisms of slowly cooled and quickly cooled copper slag in magnesium phosphate cement

Abstract

In this paper, slowly cooled copper slag (CS) and quickly cooled copper slag (QS) are used to partly replace magnesia to prepare magnesium phosphate cement. The reaction process of cement containing copper slag and the hydration product of copper slag are investigated by hydration heat, pH value, XRD, SEM, BSE and EDS tests. Meanwhile, the setting time of cement and the compressive strength of mortar are also tested. Results show that CS and QS have retarding effects on the setting of magnesium phosphate cement, and the retarding effect of CS is stronger. With the replacement of MgO by copper slag, the second exothermic peak is delayed and weakened in high w/b paste, while the precipitations of Mg2KH(PO4)2·15H2O and MgKPO4·6H2O as well as the decomposing of Mg2KH(PO4)2·15H2O are delayed in suspension. Copper slag reacts with KH2PO4 to produce amorphous ferrous phosphate hydrate. The early compressive strength of mortar containing CS is higher than that of QS. At late ages, the compressive strength of mortar containing copper slag is close to or slightly higher than that of the control sample. Both CS and QS have significant strength contributions to magnesium phosphate mortar and could be used as partial replacements of MgO in magnesium phosphate cement.