Preparation mechanism and properties of thermal activated red mud and its geopolymer repair mortar

Abstract

In order to realize resourceful utilization of red mud in environmentally friendly building materials, variation and mechanism of the reactivity with activated temperature were studied. Moreover, red mud geopolymer repair mortars were produced with activated red mud as main precursor, and the effect mechanism of water glass modulus and slag replacement ratio on their mechanical properties were clarified. Results show that dicalcium silicate is formed at 700 °C, the Si-O and Al-O bonds of aluminosilicate were broken and reduces in polymerization during thermal activation of red mud, resulting in an increase in activity index from 0.69 to 0.85. With water glass module increasing, mechanical properties of red mud geopolymer repair mortar ascends first and then decline, reaching the best when the module is 1.6, and further optimizes by the participation of slag. When replacement ratio of slag is 30 wt%, the compressive strength, flexural strength and interfacial bonding strength of red mud geopolymer repair mortar curing for 28 days are 58.5 MPa, 10.5 MPa, and 6.26 MPa, increase 77%, 114% and 58% comparing with the reference, respectively. After that, there is no discernible growth in the aforementioned properties. The incorporation of slag increases the integrity and denseness of the hardened red mud geopolymer at various curing ages, and thus improved its mechanical properties.