RECOVERY AND UTILIZATION OF SAND FROM COAL MINE OVERBURDEN DUMPS AS A SUSTAINABLE ALTERNATIVE TO NATURAL FINE AGGREGATES IN CONSTRUCTION

Mining Engineering

The rapid depletion of natural river sand due to unprecedented urbanization, infrastructure development, and escalating construction demands has created a severe resource crisis in India and across the globe. River sand, being the second most consumed natural resource after water, is being extracted at rates far exceeding its natural replenishment, causing bank erosion, riverbed degradation, groundwater depletion, and irreversible damage to aquatic ecosystems. Simultaneously, large-scale opencast coal mining operations generate enormous quantities of overburden (OB) comprising sandstone and shale formations that are typically dumped in external waste dumps, occupying vast tracts of land and causing environmental pollution. This study investigates the feasibility of recovering sand-size particles from coal mine overburden dumps and evaluating their suitability as a replacement for natural river sand in construction applications, specifically in cement mortar and concrete as fine aggregate, and in mine stowing operations. Overburden samples comprising sandstone were collected from the top sludge horizon of an opencast coal mine in India. Sand and fine particles were separated by sedimentation and decantation methods followed by sun-drying. Approximately 80% of the total overburden mass was recovered as Coal Mine Overburden Sand (CMOB sand) and the remaining 20% as Coal Mine Overburden Clay (CMOB clay). The recovered CMOB sand was characterized for chemical composition, bulk density, water absorption, particle shape, surface texture, and grading using IS-383 standards. Compressive strength of cement mortar was evaluated at replacement levels of 20%, 40%, 60%, 80%, and 100% using a 1:3 mortar mix at a water-cement ratio of 0.60. The sand segregation process involving jaw crushing, cone crushing, vertical shaft impact (VSI) crushing, screening, and hydro-cyclone washing is described in detail. Results confirm that CMOB sand falls within IS-383 Grading Zone II and exhibits satisfactory chemical and physical properties. Compressive strength of cement mortar increased progressively with increasing OB sand replacement levels, satisfying minimum strength criteria at all replacement levels including 100% substitution. The study establishes that coal mine overburden sand is a technically viable, economically attractive, and environmentally beneficial alternative to natural river sand for construction applications.

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