Effect of external sulfate attack on the mechanical behavior of cemented paste backfill

The sulfate-rich mine water in underground metal mines causes external sulfate attack on cemented paste backfill (CPB) and affects its mechanical stability. To simulate the effect of mine water environment in metal mines, CPB specimens were immersed into the sulfate solutions with different concentration (0, 0.1, 1 and 10 g/L) and cured at different times (30, 90, 160, and 240 days). Then, unconfined compressive strength (UCS) tests were conducted to investigate the effect of external sulfate attack on mechanical behavior and properties of CPB. Moreover, bulk volume change was measured at the macroscale and a series of microstructural analysis was performed to reveal the microstructure change associated with external sulfate attack. In addition, a BP neural network model was established to predict the UCS of CPB under external sulfate attack. The results show that sulfate concentration has a greater impact on the formation and crystallization of hydration products, which directly affect the pre- and post-failure behavior and bulk volume of CPB at the macroscale. Therefore, the obtained results indicate the effect of mine water induced external sulfate attack on the CPB should be fully considered for the safe design of CPB. (C) 2020 Elsevier Ltd. All rights reserved.