Acid Resistance Evaluation of Expansive and Non-expansive Calcium Sulfoaluminate Cements

When sulfate to ye’elimite ratio of Calcium sulfoaluminate (CSA) cement increases, it changes its application from rapid-strength cement to expansive (shrinkage compensating) cement. CSA cement is now getting attention because of its low carbon footprint. They are potential candidates for sewer structures where acid attack is the major durability threat. However, acid resistance of CSA is less explored. Acid resistance of commercial CSA cement (i.e., non-expansive) paste of a higher water-cement ratio of 0.6 and 0.5 were considered first. Then the mix was converted to an expansive binder by blending with 15% gypsum, and the acid resistance was evaluated. The acid resistance was evaluated by acid immersion tests with hydrochloric acid (HCl) of 1% and 2% conc., and sulfuric acid (H2SO4) of 2.95% conc. The results show that expansive CSA cement showed poorer performance than non-expansive CSA cement in acidic environment though the former had slightly higher compressive strength than the latter before acid exposure. This could be attributed to the modified phase composition in expansive CSA, as observed from the results of recently developed acid consumption tests. Similar results were observed in case of sulfuric acid attack of mortars. Though gypsum blending improved the mortar strength, the acid resistance was reduced indicating the importance of chemical composition against acid attack.