Development of unsintered construction materials from red mud wastes produced in the sintering alumina process

A large quantity of red mud (RM) has been disposed to form hills from the Chinese sintering alumina process. These storage areas are generally bare of vegetation and subject to wind and water erosion, posing serious threats to the environment. Numerous sintered products made from RM have been developed, such as ceramics, burnt bricks, cements etc., however, such sintered products have seldom been applied because of the higher energy consumption and costs. Unsintered brick was developed from RM, cured at ambient conditions. The optimal proportions of RM brick are suggested as the following: 25–40% RM, 18–28% fly ash, 30–35% sand, 8–10% lime, 1–3% gypsum, and about 1% Portland cement. Samples of RM bricks with standard Chinese brick dimension were prepared. The results show that the RM brick product reaches the Chinese criterion of the 1st-class brick. Microstructure characteristics of the RM brick were investigated by XRD and SEM. C–S–H gel and ettringite are the main hydrated products, which might contribute to the strength of brick. No sintering, drying or grinding pre-treating process, and no emission of polluting gases are some of the benefits of such an unsintered product, and which may have a huge application in the market of construction materials.