External sulfate attack on alkali-activated slag

This paper analyses the effects of external sulfate attack (5% Na2SO4 solution) on mechanical and microstructural properties of alkali-activated slag (AAS). Portland-slag cement (CEM II/А-S 42.5N) was used as a benchmark material. External sulfate attack led to a decrease in strength of CEM II, but not of AAS. Under the investigated experimental conditions, AAS showed significantly higher resistance to sulfate attack with respect to the benchmark CEM II. A very pronounced resistance of AAS to sulfate attack can be explained by the absence of portlandite and unavailability of aluminum, present in C–S–H(I) and hydrotalcite gels, for the reaction with sulfates.