Influence of steel slag powder on the characteristics of magnesium phosphate cement

Steel slag is a by-product generated during the steel manufacturing process. Currently, most of the steel slag is disposed of using land-fill rather than being recycled. In this study, we studied the effects of the substitute of magnesium oxide (MgO) with steel slag powder (SSP) on the hydration behavior, mechanical properties, phase composition and microstructure in the preparation of magnesium phosphate cement (MPC). The results showed that the addition of SSP did not lead to the formation of new crystal phases, but that the active part of SSP was activated by the high heat release and involved in the hydration process of the MPC system, generating amorphous phases. It was found that replacing MgO with 5% SSP did not reduce the weight fraction of struvite, while that of amorphous phases was increased by 2%. When 15% MgO was replaced by SSP, the weight fraction of struvite decreased by 2% but the mass fraction of amorphous phase rosed by 5%. These amorphous phases filled pores, patched cracks and connected unreacted particles with struvite to establish a continuous network. This helped to form a compact microstructure, improving the mechanical properties of MPC at a late stage. This study contributes towards a better understanding of the influence of SSP in MPC and provide an alternative for the recycling of SSP.