Experimental Study on the Physical and Mechanical Properties of Cemented Gangue Backfill under Acid Mine Water Erosion

Ensuring the structural safety of cemented gangue backfill (CGB) is crucial for safe mining operations. However, the complex mine water environment makes it susceptible to erosion by chemical ions, which have a significant time dependency. In this study, we evaluated the appearance, mass change, and unconfined compressive strength (UCS) of CGB during different chemical erosion times. We also determined the effect of chemical ion erosion time on the stress threshold for crack initiation and development in the specimens using acoustic emission (AE). Additionally, we examined the chemical erosion mechanism of CGB by scanning electron microscopy (SEM). Our results showed that as the erosion time increased, the CGB exhibited a decrease in brittleness and an increase in plasticity. During the first 60 days of CGB, the internal micropores and microfractures of the CGB were filled due to the hydration reaction and SO₄²⁻ intrusion, resulting in increases in the UCS and the mass of the CGB. However, as the erosion time continued, H⁺ and SO₄²⁻ intruded into the interior of the CGB, causing the erosion products of the CGB to expand in volume, leading to a decrease in the strength of the CGB. Our analysis of the stress thresholds for microcrack development and macrocracks initiation in the CGB showed an increase followed by a decline with time. After 60 days of immersion, the stress threshold for microcrack initiation and macrocrack extension increased by 20% and 6%, respectively. However, as the immersion time increased to 150 days, the stress threshold for microcrack initiation and macrocrack extension decreased by 56% and 16%, respectively. Therefore, the design of CGB safety needs to consider the long-term effects of chemical attacks on CGB.