Development and evaluation of coalmine waste materials for gainful utilisation

Coal mine overburden as well as thick inseam parting materials found in the lower Gondwana basin are often treated as mine wastes. Unused fly ash from coal fired plants is another waste material. This investigation focused on using these wastes to develop better composite materials. Composite materials of varying composition with coal mine wastes from 50% to 90% and fly ash from 10% to 50% were developed with 2 to 6% cement additives. Their physical, chemical and geotechnical properties were determined. OPC strongly influenced the geotechnical properties. Fly ash presence were optimized for unconfined compressive strength (UCS) and California bearing ratio for both the mine wastes. Composite materials with 70% overburden, 30% fly ash, and 6% cement showed 4.01 MPa UCS at 56 days. Similarly, 80% inseam parting, 20% fly ash, and 6% cement produced 4.90 MPa UCS at 56 days. Analysis of fly ash present in the two composites and their strength values produced linear correlations. Pearson and Spearman’s coefficients produced high correlation of −0.9 for the composite prepared with parting materials. Microstructural analysis showed C-S-H gel formation occurring at 28 days. The composites meet the strength criterion for the base and sub-base of the coal mine haul road.