Early-age characteristics of red mud–coal gangue cementitious material

Abstract

This experimental research was to investigate the possibility of incorporating red mud and coal gangue as raw materials for the production of red mud–coal gangue cementitious material, abbreviated as RGC, including analyses of its chemical composition, physical properties, mechanical properties and hydration products. The red mud and coal gangue (at a ratio of 3:2) were mixed together and shaped in small spheres with a water to solid ratio of 0.30 and then calcined at 600 °C for 2 h. Subsequently, the RGC was prepared by blending 50% the resultant red mud–coal gangue mixtures, 24% blast-furnace slag, 20% clinker and 6% gypsum. The hydration products of RGC were characterized by XRD, TG-DTA and SEM-EDS. The results showed that it is feasible to use red mud and coal gangue to replace up to 50% of the raw materials to produce cementitious material, which can be called as silica–alumina based cementitious material. The hydration products of RGC are mostly ettringite, calcium hydroxide and C–S–H gel. As the dominant products, C–S–H gel and ettringite are principally responsible for the strength development of RGC in early hydration process. The content of Ca(OH) 2 initially increased but later was depleted after reaching the peak value at 21 days. Moreover, it is found that the composition of the C–S–H gel shifted towards higher Si, Al and Na contents with the increase of hydration age, whereas that of Ca shifted towards lower content.