Parameters controlling loss of mass and stiffness degradation of ‘green’ stabilised tailings

Abstract

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.