Unidirectional penetration approach for characterizing sulfate attack mechanisms on cement mortars and pastes

Degradation of cementitious materials by sulfate ions is commonly classified into chemical and physical sulfate attack. So-called "physical" attack dominates in many field situations, but laboratory testing focuses on "chemical" attack under full-immersion. This paper presents a new setup which looks at sulfate ion ingress under unidirectional capillary action, as a first approach to field conditions. Here, a high concentration of sulfate ions and w/c and Portland cement were used to accelerate degradation to see if the approach is feasible. The radial expansion and appearance of mortar and paste samples were tracked over time. Periodically, profiles of sulfate ingress and phase assemblage were studied in the SEM and by X-ray diffraction. The results show that physical and chemical sulfate attack occur in different areas of the same sample. The approach shows potential to uncover the mechanisms involved in sulfate attack including both "chemical" and "physical" aspects of the degradation process.