ALKALINE-ACTIVATED STEEL SLAG–RICE HUSK ASH GEOPOLYMERS FOR GOLD MINE TAILINGS STABILIZATION AND SUSTAINABLE ROAD CONSTRUCTION: A CRITICAL REVIEW

Abstract

The increasing generation of mine tailings, metallurgical slags and agricultural residues has created a combined environmental-management and resource-efficiency challenge for the construction sector. Gold mine tailings (GMT) are particularly difficult to reuse because their fine-grained nature, variable mineralogy, potentially toxic elements and susceptibility to contaminant release can limit direct application in pavement earthworks. At the same time, steel slag (SS) and rice husk ash (RHA) are locally available wastes with complementary chemical characteristics that can be exploited through alkaline activation. This review synthesizes the engineering and environmental evidence on SS–RHA-based alkali-activated/geopolymeric binders for stabilization of mine tailings, with emphasis on pavement applications. The review examines the characteristics and reactivity of GMT, SS and RHA; mechanisms of alkaline activation; effects of precursor proportion, particle size, activator chemistry, water content, curing and Si/Al-related ratios; and resulting changes in plasticity, compaction, California Bearing Ratio (CBR), unconfined compressive strength (UCS), hydraulic conductivity and contaminant leachability. Evidence indicates that steel slag can contribute calcium-rich reactive phases and particle interlocking, while RHA provides a highly siliceous source that participates in the formation of binding gels under alkaline conditions. Their combination can therefore provide both mechanical improvement and immobilization of potentially toxic elements. However, performance is strongly mixture- and source-dependent, and excessive RHA, excessive alkalinity, unsuitable activator ratios, inadequate curing and insufficient particle-size control can reduce performance or increase environmental risk. The review identifies the need for integrated multi-response optimization, standardized leaching assessment, field-scale validation, life-cycle assessment and economic analysis. A research framework is proposed for developing locally sourced SS–RHA geopolymeric binders for sustainable pavement construction in Nigeria and other regions where mining, steel production and rice processing generate significant waste streams.