Optimisation of binder alternative for cemented paste fill in underground metal mines

Abstract

To maximise ore recovery safely and economically, a proper backfill design of required strength is imperative to facilitate extraction of adjacent stopes. Ordinary Portland cement (OPC) has a direct impact on the strength gained by the paste fill mix and is also a major contributor to the backfilling cost. This has prompted the users to go for partial replacement of OPC with readily available industrial wastes such as fly ash and jarosite to obtain a paste mix of desired strength. This paper highlights the use of a mathematical model to predict the strength requirement (unconfined compressive strength and cohesion) of self-supporting paste fill for secondary pillar extraction of stopes in metal mines. This paper also highlights extensive laboratory investigation carried out for partial replacement of OPC with fly ash and jarosite to map the changes in the strength of paste mix with time. Initially, the percentage of OPC required to achieve the designed strength was evaluated and subsequently, the percentage of OPC in the mix was replaced gradually with fly ash and jarosite. Laboratory results indicated that the strength of the paste mix increases with curing period (7, 14, 28 and 56 days) and the chemical composition of the ingredients also played a major role in strength development. The results were then compared with the required strength predicted from the model to obtain proper paste mix for existing mine’s stope dimension.