Performance of concrete with blended binders in ammonium-sulphate solution

Abstract

Concrete elements in agricultural, wastewater treatment, mining, and industrial applications can be vulnerable to chemical attack by ammonium-based solutions. In particular, ammonium sulfate (commonly used as a fertilizer) is extremely deleterious to concrete. This is due to its dual acid–sulfate action, which may disintegrate the hydrated cement paste to various levels based on the prevailing exposure conditions and key mixture design parameters of concrete. The aim of this study was to investigate the response, in terms of physico-mechanical and microstructural features, of concrete comprising different types of cement (general use [GU] or Portland limestone cement [PLC]) with various combinations of supplementary cementitious materials (SCMs: fly ash, silica fume, and nanosilica) to a severe ammonium sulfate exposure. The study comprised 12 months of immersing test specimens in 5% ammonium sulfate solutions with a pH level of 6.0–8.0. The results revealed that the type of binder along with the dosage and nature of SCMs dictated different modes and levels of deterioration, and consequently the physico-mechanical trends of concrete were characterized by softening with (single binders) or without (blended binders) significant expansion. PLC may slightly improve the resistance of concrete to ammonium sulfate attack, whereas among the blended binders tested, binary binders comprising 5% silica fume, 5% nanosilica, or 30% fly ash improved the resistance of concrete to this type of chemical attack.