Durability and heavy metals leaching behavior of cemented paste backfill using chemical activated binary slag as binder under sulfate attack

Abstract

The present study conducted an extensive investigation into the durability of Na2SO4-activated binary slag cementitious materials for use in cemented paste backfill (CPB) under sulfate attack conditions. The primary objectives were to assess the feasibility of employing a cost-effective and environmentally friendly binder in CPB applications. Samples were subjected to exposure to Na2SO4 and MgSO4 solutions for a duration of 30 weeks, and multiple aspects including dimension stability, micro and macro mechanical strength evolution, changes in phase assemblage, microstructure following sulfate attack, and heavy metals leaching were examined. The study revealed that Na2SO4-activated binary slag (OPC-slag/S) exhibited superior resistance to sulfate attack, demonstrating enhanced dimension stability. Notably, sample OPC-slag/S displayed an increase in compressive strength, even after prolonged exposure to sulfate solutions for 30 weeks. This increase amounted to approximately 10.76% and 4.81% following exposure to Na2SO4 and MgSO4 solutions, respectively. The heightened resistance of binder OPC-slag/S to sulfate attack can be attributed to its low portlandite content and the early consumption of aluminates, primarily due to the formation of ettringite. This phenomenon effectively prevents the formation of detrimental and expansive products within the cement matrix during sulfate attack. On the other hand, CPB samples with binder OPC-slag/S showed the best performance in heavy metals immobilizaton capacity due to the high resistance to sulfate attack. In conclusion, this study underscores the potential of utilizing OPC-slag/S as a cost-effective and environmentally friendly binder for CPB applications in sulfate-rich environments.