Properties of red mud blended with magnesium phosphate cement paste: Feasibility of grouting material preparation

In order to reduce Portland cement usage in underground engineering, and solve the problem of red mud pollution, a new red mud-magnesium potassium phosphate cement (MKPC) based grout (RMG) was prepared. The mechanism of red mud on MKPC was investigated and the workability and microstructure of RMG were studied with different red mud contents. The results show that red mud improves the properties of MKPC, both by a chemical reaction and a micro-aggregate effect. The setting time of RMG is prolonged with the increment of red mud content, the compressive strength increases first and then decreases with the increment of red mud content, showing a threshold value of 50 wt% both for setting time and compressive strength. The fluidity of RMG has a positive relationship with red mud content. In order to obtain good workability, the admixture of red mud should be set between 30 wt% and 50 wt%. X-ray diffraction (XRD), Fourier Transform Infrared spectra (FT-IR), Scanning Electronic Microscopic-Energy Dispersive Spectrometer (SEM-EDS) and Mercury intrusion porosimetry (MIP) were carried out to analyzed the microstructure of RMG. The analysis showed that MgKPO4·6H2O is the main hydration product in RMG, Al, Fe, Na were founded in the hydration products by SEM-EDS and FT-IR, and red mud can reduce the porosity of MKPC proved by MIP.