Sustainable circular co-disposal of mining waste for cost efficiency

Abstract

The accumulation of waste tyres presents a significant environmental challenge, demanding innovative recycling solutions. Simultaneously, cemented rock fill (CRF) implemented in underground stoping mining methods presents tensile strength limitations, resulting in stability issues during horizontal (overhead) exposure. As such, there is benefit to reinforce CRF against tensile stresses. Given the vast volume of CRF used in mining operations, it is difficult to find a suitable reinforcing material that is also economical and sustainable. This study explores the incorporation of waste tyre rubber into CRF to develop tyre-enhanced cemented rock fill (TCRF), addressing both waste tyre recycling and CRF strength deficiencies. Large-scale experimental investigations, including compressive and tensile strength were conducted including waste tyre rubber from 5.5 % to 33 % of the cemented rock fill by volume. Results indicate that while the inclusion of waste tyre rubber reduces compressive strength and modulus, it significantly enhances tensile strength—a crucial parameter for backfill stability. A mix design of 3 % cement and 22 % waste tyre rubber achieved a tensile strength comparable to conventional CRF with 5 % cement, enabling potential cement savings of AU$ 8 per cubic meter of CRF through the removal of 2 % cement content for the same performance. Furthermore, the waste tyre rubber addition improved ductility and post-failure strength behaviour, further increasing the stability of backfilled exposures. As such, this research highlights TCRF as a sustainable and cost-effective solution for underground mining backfill, advancing waste tyre recycling and optimizing material cycles in mining operations.