This study evaluates the alkali activation of a binary system composed of sugar cane bagasse ash and carbide lime as a green stabilization technique for bauxite tailings (BTs). To analyze the feasibility of this alternative binder as a stabilizer, mechanical tests were performed to measure the strength, stiffness, and durability of BT binder mixtures. As a control group, tailings were stabilized with high-initial-strength portland cement (Type III). The results show that the alternative binder is a suitable option to improve the mechanical behavior of bauxite tailings. The porosity/binder index ($\eta /B_{iv}$ ) was an appropriate parameter for evaluating BT stabilization. Reduced porosity and increased binder content (decreased $\eta /B_{iv}$ ) led to an improvement in the mechanical behavior of the studied mixtures.

The present study makes three contributions to the literature of expansive soils: (i) it proposes equations to predict soil swelling based on dry density and cement content, (ii) it checks the developed general equation by predicting the swelling of different expansive soils from the literature, and (iii) it designs experiments that investigate factors that have a significant influence on swelling. An experimental programme was carried out to analyse the expansion of bentonite–kaolin–cement blends. Different proportions of bentonite–kaolin, cement content, dry density, and moisture content were evaluated. A unique relation of the cement/porosity index was obtained for cement-stabilized expansive soils’ swelling; this index has been used before to portray strength, stiffness, and loss of mass of stabilized soils and is now shown to be applicable to describe swelling of expansive soils treated with Portland cement. In the present research, cement content and dry density are seen as conflicting parameters regarding the swelling of expansive soils, because increasing the amount of Portland cement reduces swelling and increasing the density (through compaction) causes higher expansion. A general swelling model is proposed and successfully checked with data from the literature; it is able to predict the swelling of expansive soils with different densities, expansive mineral, moisture content, and cement content.

Effective binders with low environmental impacts are of great importance for sustainable engineering practices. Parameters controlling loss of mass and stiffness degradation of ‘green’ stabilised bauxite tailings (BT) were evaluated. The porosity/binder index (η/Biv) was investigated. This index allows unification of all experiments in a single relation for a specimen's porosity and binder content, resulting in a rational dosage methodology for any soil–binder blend, replacing conventional (trial and error) strategies that are laborious and time consuming. Wetting–drying cycles (durability tests) and pulse velocity tests were performed. The alkali-activated binder was composed of sugarcane bagasse ash and carbide lime (precursors) and sodium hydroxide (alkaline activator). For comparison, BT were also stabilised with Portland cement. For both cementing agents, stiffer specimens were less susceptible to the abrasive action of durability cycles. Diverse stiffness behaviours were observed due to the different curing periods needed for the development of chemical reactions for each binder. η/Biv was found to be an appropriate parameter for evaluation of loss of mass and stiffness degradation: lower porosity and higher cement content resulted in better mechanical performance. Through η/Biv, engineers can choose the best option for a project by decreasing porosity (increasing soil compaction) and reducing the binder content or, inversely, increasing porosity while raising binder content.