Some properties of flyash for mine backfilling

Abstract

Back filling of mine voids is mandatory to avoid subsequent ground stability problems in the form of subsidence. Mill tailings and river sand are being extensively used since a long time as mine back filling materials. However strict regulation and unavailability of river sand has created a huge problem for mining industry in India. The need to develop alternative engineering material which can substitute sand has gained prominence. Large quantities of fly ash discharged from coal-fired power stations are a major problem not only in terms of scarcity of land available for its disposal, but also in psychology as well as environmental aspects. Amount of fly ash available can be recycled, mainly by adding fly ash to cement. However, the addition of fly ash to cement is limited because the production rate of cement is limited, and also the concentration of fly ash in cement is limited. In the present study three fly ash composite materials (FCMs) were developed from the fly ash obtained from a nearby captive thermal unit. The main constituent of the composite were fly ash, lime, gypsum and cement. Detailed physical and engineering properties were determined for the FCMs. Significant increases in the compressive strength were obtained after 28 days of curing time and it was observed that the fly-ash composite developed has potential to be used as substitute to sand for back filling the mine voids.