Hydration characteristics of red-mud based paste-like backfill material

Preparation of red-mud based paste-like backfill material using red mud, coal gangue, and other industrial solid wastes was accounted. In order to understand the hydration characteristics of red-mud based paste-like backfill material, X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric-differential scanning calorimetry, and scanning electron microscope-energydispersive X-ray spectroscopy techniques were used to investigate the hydration products of the hardened paste, which was formed after hydration of raw materials. The results show that the most optimized proportion is the number E03 experiment, in which the mass ratio of cementing material, red mud, coal gangue, and additive agent is 1:16:5:11, the solid mass fraction is 70%, and the uniaxial compressive strength after 28 days is 5.49 MPa. The hydration products of red-mud based paste-like backfill material are mainly gismondine (CaAl2 Si2O8·4H2O) and ettringite (AFt). As the hydration reaction proceeds, the quantity of hydration products increases significantly. Needle-shaped ettringite forms during the early hydration period and gradually transforms into rod-shaped ettringite; this transformation is helpful in the strength development of the red-mud based paste-like backfill material.