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AbstractMassive 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.

A large number of mixed soils exist in nature, including sand–clay mixtures, silt–clay mixtures and clay–clay mixtures. The physical parameters of soils are the basis for investigating their mechanical properties (compression, permeability, strength). More importantly, the liquid limits play an important role in establishing the relationships between physical and mechanical properties. The liquid limit tests of sand–clay mixtures were performed on different kinds of original clays with different sand contents. These data together with those compiled from the literature were used to investigate the change in liquid limits of mixed soils. The results show that the liquid limits of mixed soils are influenced by the types of original soils and the contents of each constituent. In sand–clay mixtures, the liquid limits increase with the increasing clay contents. The empirical equation is proposed to predict the liquid limits of sand–clay mixtures based on the liquid limits of original clays and clay contents. By analogy, the method for predicting liquid limits of mixed soils including two types of original soils with known liquid limits is acquired, such as silt–clay mixtures and clay–clay​ mixtures. Such a method is also extrapolated to the mixed soils with more types of original soils.

Determining the compressibility of slurry with high water contents via self-weight consolidation test usually requires excessive testing time. To overcome such shortcoming, double drainage self-weight sedimentation test (DDSST) is used in this study. The stress equilibrium at the steady state under double drainage condition is analysed, based on which the relation between effective stress σ′and the distribution of water contents is investigated. Accordingly, the procedure for calculating σ′- erelation with obtained distribution of water contents is presented. To verify the feasibility of determining σ′- erelation of slurry with DDSST, DDSSTs were conducted on two types of slurry. Calculated results according to the given procedure show that, the σ′- erelation obtained via DDSST is basically the same with the one obtained via single drainage self-weight sedimentation test (SDSST), which demonstrate the effectiveness of DDSST in determining the compressibility of slurry. Furthermore, using DDSST rather than SDSST could significantly shorten the testing time and reduce experimental material usage.