Durability test methods and their application to AAMs: case of sulfuric-acid resistance

Abstract

Alkali-activated materials (AAMs) are new binders considered as alternatives to ordinary Portland cement (OPC). These materials differ from OPC in structure and chemistry. In recent decades, durability test methods have been developed for OPC and blended OPC chemistry, but using these methods to characterize AAMs durability could yield incorrect results. This paper reports on a study on alkali-activated class F fly ash (AAFA), alkali-activated blast-furnace slag (AAS), and OPC (used as a reference) to determine the appropriateness of the acid-resistance test method for AAMs. As there is no specific standard for acid resistance, ASTM C267 was used as a basis. The influence of the acid concentration and curing time were assessed by measuring changes in mass and cross-sectional dimensions, visual inspection and compressive strength over time. Changes in the curing time from 7 to 28 days indicate no significant difference in the results for the three systems. The results reveal a different deterioration process for each material. The OPC specimens evidenced a decrease in mass and cross-sectional dimensions. The AAS showed a mass gain and expansion. In both cases, gypsum formed as a corrosion product. While the mass and shape of the AAFA specimens appeared constant, SEM results revealed dealumination and dealkalinization of the sodium aluminosilicate gel, corroborated with a loss of compressive strength. In addition, due to the low calcium content, a small quantity of gypsum was formed. This work clearly demonstrates that the indicators of the degree of attack described in ASTM C267 are not appropriate for use in comparative studies involving AAMs due to the differences in the deterioration processes.