Strengthening mechanism of red mud with calcium oxide

Abstract

Currently, the utilization rate of red mud is very low, and the problems of occupying land and polluting the environment are becoming increasingly prominent. This study utilized CaO to prepare Red Mud-based cementitious material (RMC) to achieve clean and efficient utilization of red mud. The mechanism of Ca2+ enhancing the strength of RM and the carbonation reaction in RMC were studied using X-ray diffraction (XRD), Fourier transform infrared spectrum (FTIR), Thermogravimetric Analysis (TGA), Scanning electron microscopy (SEM) and other analysis methods. The results showed that the carbonization of CaO in RMC bonded the red mud particles and provided early strength. CaO activated the components of gibbsite, diaspore, and silica in RM, and hydration reaction generated gel-like Al-substituted tobermorite (Ca5Si5Al(OH)O17·5 H2O), ensuring the increase of later strength. At the age of 28 days, the RMC with a CaO content of 25% had the highest unconfined compressive strength, reaching 2.19 MPa. When the CaO content exceeded 25%, the compressive strength of RMC gradually decreased. This is due to the reaction of calcium carbonate and aluminate to form a large number of sheets of calcium aluminate monocarbonate (Ca4Al2O6CO3·11 H2O), which weakened the carbonation binding effect and competitively consumed aluminate, resulting in an increase in structural cracks and pores, and a decrease in the compressive strength of RMC.