Durability of Calcined Clay-Included Alkali-Activated Cement Pastes Against Sulfuric and Hydrochloric Acid Attacks

Nowadays, concrete is one of the most manufactured items globally; thereby, utilizing sustainable resources to produce concrete can significantly contribute to preventing human beings from harming the environment. Alkali-activated binders, also named “geopolymers,” have been proposed as a Portland cement alternative since, besides lowering CO2 emissions notably, they need less energy to be produced. In this study, using ground granulated blast furnace slag (GGBFS) as the precursor and sodium hydroxide, sodium carbonate, and sodium silicate as the activators, 27 alkali-activated binders with various mixture proportions were prepared. For each activator, in addition to three different “solid part of the activator/precursors” ratios (5%, 7.5%, and 10%), GGBFS was substituted with three different amounts of calcined clay (0, 10, and 20 wt.%). After being cured for 28 days, test specimens were immersed in the sulfuric acid and hydrochloric acid solutions, and the degree of deterioration was examined in terms of weight loss. Results indicate that, in general, alkali-activated pastes are less durable in sulfuric acid solution than in hydrochloric acid solution. Furthermore, it was observed that in most cases, an increase in the calcined clay content and “solid part of the activator/precursors” ratio is followed by more weight loss of alkali-activated pastes in acidic solutions. Additionally, while alkali-activated binders containing sodium hydroxide as an activator exhibit the highest weight loss, those cast using sodium silicate demonstrate the lowest weight loss after being submerged in acidic solutions.