Sulfuric acid and citric acid attack of calcium sulfoaluminate-based binders

Abstract

Calcium sulfoaluminate (CSA) cement-based binders are low CO2 binders which exhibit rapid hardening or shrinkage compensating characteristics. Due to their unique properties, they have potential to be used in concrete elements exposed to acidic environment such as sewage system. In this paper, the performance of CSA-based binders in acidic environment is examined and compared against Portland cement (PC). Attack of sulfuric acid and citric acid on PC and CSA-based binders was evaluated with respect to mass loss, dimensional change, cumulative H+ ion neutralisation, strength loss, and changes in mineralogical and microstructural characteristics. CSA-based binder exhibited higher resistance than PC-dominated binder in citric acid attack (pH ∼ 2–3), whereas PC-dominated binder outperformed CSA-based binder in case of sulfuric acid attack (pH ∼ 1.5–2). The mechanism of acid attack was found to be dependent on acid type. A calcium citrate salt was identified as the major product in case of citric acid attack of PC-dominated binders.