Investigation on properties and mechanism of non-calcined Bayer red mud-phosphogypsum cementitious binder

China produces a large amount of red mud (RM) and phosphogypsum (PG) each year. At this stage, there is an urgent need for a process that can use a large number of these wastes to reduce the pressure of stacking cost and environmental pressure. In this study, an improved high-strength and non-calcined RM-PG cementitious binder was developed. Under a certain mixture ratio, the cementitious binder is prepared from non-calcined Bayer RM and PG, with granulated blast furnace slag (GBFS) and alkaline activator. The RM-PG cementitious binder has a compressive strength of more than 40 MPa. A large amount of RM and PG were added, and their activities could be better stimulated under strong alkaline condition. The performance of the cementitious binder can be improved by adding different substitutes instead of GBFS. The strength formation and hydration mechanism of the non-calcined cementitious binder were discussed by analyzing the X-ray diffraction (XRD), scanning electron microscope (SEM) and pH of the leaching solution. Results indicate that various raw materials undergo different degrees of dissolution in an alkaline environment. They continuously generate C-S-H, C-A-H gels and Ettringite (AFt) to develop mechanical strength of the RM-PG cementitious binder. The result provides a new way for the coordinated utilization of two kinds of industrial wastes. The new cementitious binder is more environmentally friendly and has a great application prospect.