Sulfate Induced Degradation of Alkali Activated Materials

AAMs demonstrate variable resistance to sulfate attacks depending on their composition and environmental exposure, complicating their widespread use in construction. This chapter reviews global standards for sulfate resistance testing and highlights the limitations of using OPC-based methods for evaluating AAMs. It discusses the sulfate resistance of low-, intermediate-, and high-calcium AAMs, with a focus on their degradation behaviors in the presence of sodium sulfate (Na2SO4) and magnesium sulfate (MgSO4) solutions. This chapter emphasizes that low-calcium AAMs, particularly geopolymers, generally exhibit strong resistance to Na2SO4 but are susceptible to MgSO4-induced degradation. For high-calcium AAMs, such as alkali-activated slag (AAS), sulfate attack can cause significant strength loss, particularly in the presence of MgSO4, which accelerates the formation of deleterious products like gypsum. Efforts are needed for nanoscale investigations into sulfate attacks on AAMs and updated standards and testing methods tailored to the unique chemistry of AAMs.