Effect of sulfate content on the evolutive fracture behavior and properties of fiber-reinforced cemented paste backfill

Abstract

Backfilling technology is utilized globally to improve ore recovery, reduce mine-generated waste, and provide stability to underground voids. Cemented paste backfill (CPB), a mixture of mine tailings, cement binder, and mixing water is the desired method of backfilling. After filling the underground space (called a stope), CPB is required to provide ground resistance to the surrounding rock walls, be used as a roof for continued mining operations, or a floor for underground mine workers and equipment. A challenge to the use of CPB is the vast quantities of sulfide minerals such as pyrite and pyrrhotite containing irons present in the waste mine tailings. The sulfate anions generated from the oxidation of sulfide minerals not only interfere with the progression of cement hydration but also produce expansive hydration products, including gypsum and ettringite. As a result, the sulfate anions are able to change the microstructure and macroscale geomechanical behavior and material properties of the CPB materials. Therefore, it is of theoretical and practical importance to fully consider sulfate-induced evolution of mechanical behavior and properties of CPB materials. Moreover, the ability to extract ore up to the CPB pillar provides benefits to the profitability of the mine. However, mine stopes may reach enormous depthsin excess of 100m into the earth. Therefore, the CPB is not only subject to the internal chemical effects of the sulfide minerals but also to the complex loading conditions present within the mine stope. As a type of brittle material, the failure processes in the CPB matrix are governed by crack propagation under field loading conditions. Such an event will not only reduce mine profitability but can also potentially be life-threatening to the underground workers. As a method to mitigate such risk, fiber reinforcement (FR-CPB) is a promising approach. Hence, it is crucial to systematically investigate the effect of sulfate solution on the tensile and fracture behavior and properties of fiber-reinforced CPB materials. [...]