External sulfate attack on alkali-activated slag

Abstract

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/A-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.