Preparation, characterization and application of red mud, fly ash and desulfurized gypsum based eco-friendly road base materials

Abstract

Red mud (RM), fly ash (FA) and desulfurized gypsum (DG) are harmful solid wastes that need to be treated. In this study, RM, FA, DG were used as the main raw materials to prepare road base materials based on the different (CaO + Na2O)/(SiO2+Al2O3) molar ratio, and its mechanical properties, durability, microstructure and environmental performance were investigated. The morphology and structure were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR), Thermogravimetry-derivative thermogravimetry (TG-DTG), Scanning electron microscopy energy dispersive X-ray (SEM-EDX), Mercury intrusion porosimetry (MIP). The results show that the road base material prepared by RM-FA-DG composites has the highest unconfined compressive strength (UCS) after curing for 7 days when (CaO + Na2O)/(SiO2+Al2O3) = 0.88, which meets the strength requirements of the highway. The UCS of the road base material still increased significantly after curing for 28d and reached 11.49 MPa at 180d. Meanwhile, the best durability is obtained by RM-FA-DG composites. The main hydration products of RM-FA-DG composites are C-A-S-H gel, ettringite and zeolite phase (such as Al2Si2O4(OH)4, Na2Ca2Si5Al5O10·5H2O), which are very beneficial to the development of the compressive strength and durability of road base materials. The best polymerization structure and the pore structure are also obtained by RM-FA-DG composites. The leaching results show that the RM-FA-DG system can effectively consolidate Na+ and other heavy metal ions, and the leaching concentration of ions all meet the drinking water standard of China. In addition, the research has been successfully applied to pilot test in Yangquan, China. Therefore, RM-FA-DG synergistic prepare road base material provides a new idea of synergistic to effective utilization of a large number of industrial solid wastes.