Microstructure, mineralogy and environmental evaluation of cementitious composites produced with red mud waste

Red mud (RM) is a by-product from aluminum industry, and represents a renewed environmental problem due the significant annual throughput by the plants. The investigation of the microstructure and mineralogical compositions of the cement pastes with up to 15% of dry or calcined RM (600–900 °C) were carried out using scanning electron microscopy, X-ray diffraction and differential thermal analysis techniques, respectively. The environmental evaluation of RM was performed using Toxicology Characteristic Leaching (TCLP) and diffusion tests in mortars. Water absorption by capillarity, wetting angle, compressive strength tests were carried out on mortars with up to 15% RM in replacement of cement. The compounds calcium silicate hydrate, AFm phase, CAH gel and ettringite were identified in the pastes produced with RM. The results showed that the RM waste can be used in replacement to cement to produce cementitious composites with microstructure, mechanical and hygroscopic properties suitable for their use in civil construction.