Response of concrete with blended binders and nanoparticles to sulfuric acid attack

Abstract

Concrete has long been the most popular material for the construction of key infrastructural elements such as sewerage pipes, water treatment facilities, industrial floors and foundations, which can be chemically vulnerable to damage by sulfuric acid attack. Since high alkalinity is required for stability of the cementitious matrix, concrete is susceptible to attack by acidic media, which may disintegrate the hydrated cement paste to various levels based on the prevailing exposure conditions and key mixture design parameters of concrete. This study investigated the response, in terms of physico-mechanical and microstructural features, of concrete comprising different types of cement (general-use or Portland limestone cement (PLC)) with various combinations of supplementary cementitious materials (fly ash, silica fume and nanosilica) to severe sulfuric acid exposure (immersion of test specimens in 5% sulfuric acid solution with a maximum pH threshold of 2·0 for 90 d). The results revealed that the surface degradation (mass loss) of concrete under severe sulfuric acid attack was independent of its penetrability (physical resistance), since very dense cementitious matrices (low penetrability) suffered severe deterioration. PLC may slightly improve the resistance of concrete to sulfuric acid attack whereas, among the blended binders tested, binary binders comprising 30% fly ash particularly improved the resistance of concrete to sulfuric acid attack due to an inert filler effect of fly ash particles at the exposed surface.