Effects of water purifying material waste and red mud on performance of magnesium phosphate cement

Abstract

In view of the limitations of the excessive hydration rate and poor water resistance of magnesium phosphate cement (MPC), the effects of water purifying material waste and red mud on the mechanical properties and water resistance of MPC were studied. Furthermore, we analyzed the changes of the hydration properties and microstructure in the MPC due to the addition of these materials. The results showed that the incorporation of water purifying material waste and red mud provided crystallization sites for the MPC hydration products, which improved the strength and water resistance at 14 and 28 d. There was a significant amount of unreacted MgO after MPC curing, and the main hydration product was struvite-K. When the water purifying material waste or red mud was added alone, the strength and water resistance of the MPC at 14 and 28 d were improved, and the higher the added content was, the better the water resistance became. Moreover, when water purifying material waste and red mud were doped together, the compressive strength at 1 and 3 d decreased, while that at 14 d increased. The maximum compressive strength was 54.70 ± 1.60 MPa when the dosage reached 4.0 wt%. We found that the water resistance at 7 d improved, and the softening coefficient reached 0.84 at a 6.0 wt% dosage. Thus, this research not only provides a reference for MPC modification methods but also provides a new method for the resource utilization of solid waste.