Alkali-activated red mud in stabilizing marine dredged clay with low amount of cement

Massive landfilling of red mud (alumina residue, RM) has posed a great challenge to the sustainable development of the alumina industry. To consume such vast industrial wastes, it is of great benefits to promote reuse of RM in land reclamation to replace partial traditional cementitious materials. This study investigates the potential use of the RM in stabilizing marine dredged clay (MDC) with a low dosage of cement, where sodium silicate is used as an alkali-activator. A series of laboratory tests are performed to characterize positive role of alkali-activated RM in improving mechanical and microstructural properties of cement-treated MDC. The variation of strength, permeability and micro characteristics are examined with different RM contents, sodium silicate contents and curing time. The results indicate an optimal content of sodium silicate regardless of curing time, which grows from 10% to 20% when RM content increases from 5% to 15%. Both hydration and polymerization reactions occur in the mixture of MDC, cement and alkali-activated RM, generating products including hydration gels (C–S–H and N–A–S–H) and geopolymer (analcime, faujasite and unnamed zelites). With optimal content of alkali, the stacked structure combining quadrate crystal clusters and gels can be observed, which contributes to significant strength improvement of stabilized MDC.