Acid attack is a major durability problem in concrete structures exposed to acidic environments such as concrete pipes carrying sewage. Chemical acid attack is further exacerbated in the presence of bacteria such as thiobacilli and called biogenic acid attack. Portland cement (PC)-based binders exhibit poor resistance against acid attack. Hence, there is a need for a sustainable and superior alterative to PC. Among potential alternative binders, calcium sulfoaluminate (CSA)-based binders are low CO2 binders which exhibit rapid hardening or shrinkage-compensating characteristics. There are limited number of studies on acid resistance of CSA-based binders as the composition of CSA-based binder can vary significantly altering its properties (e.g., strength, rapid hardening and expansion characteristics). This study aims at evaluating the relative performance of CSA-based binder in different acidic environments (i.e., strong and weak acids).
This seminar discusses in detail the potential of acid consumption as a novel criterion in differentiating acid resistance of binders. Two types of acids (i.e., citric acid and sulfuric acid) and three cementitious binders (i.e., PC, high ye’elimite CSA cement, and calcium aluminate cement (CAC)) were utilized in this study. The tests were performed on monolithic specimens as well as powdered hydrated samples using an autotitrator. Based on acid consumption tests on monolith and powder samples, CSA cement performed better than PC, but inferior to CAC in citric acid attack (pH 3). Further, CSA cement outperformed both PC and CAC in sulfuric acid attack (pH 1). The presentation also discusses results of a long-term (duration of one year) field study to evaluate in-situ biogenic acid resistance of binders. The presentation highlights that pH reduction in CSA-based binder was initially rapid, but, ultimately, its biogenic acid resistance was found to be better than that of PC. The underlying mechanism identified from characterisation tests will also be discussed.