Characterization studies on coal gangue for sustainable geotechnics

Global rise in greenhouse gas emissions (GHG) is triggered mainly due to the consumption of fossil fuels for power generation and domestic usage. Among the fossil fuels, coal is a primary contributor to global GHG with substantial emissions generated during its mining and combustion process. Coal gangue, a residue produced during the coal mining process, has found sparse utilization in civil engineering applications. To gauge the feasibility of using coal gangue for geotechnical and geoenvironmental applications, comprehensive characterization study was performed which include understanding the geotechnical, mineralogical, chemical and leaching behavior. Further, to evaluate the environmental impacts associated with coal gangue utilization, carbon footprint assessment (CFA) was performed. The geotechnical properties of coal gangue revealed its potential as fill material in the construction of embankments and retaining walls. Mineralogical and chemical characteristics of coal gangue are comparable to coal combustion residues like coal ash and fly ash which are widely used in bulk civil engineering applications. The leaching studies revealed the presence of trace elements in coal gangue; however, their concentration levels were found to be well below permissible limits. The CFA has shown that utilization of coal gangue in mechanically stabilized earth wall construction resulted in a net savings of 1709 CO₂ (kg) emissions. Based on the characterization studies, it can be inferred that coal gangue is a potential alternative to the existing conventional geomaterials like soils and other recycled materials.