Resistance of Alkali-Activated Binders to Organic Acids Found in Agri-Food Effluents

Abstract

Organic acids, such as acetic and lactic acids, are prevalent in agricultural and food effluents. They pose a considerable pollution threat and must be collected and stored safely before treatment and release. They cause significant damage to cementitious materials, reducing the service life of structures. In this study, the resistance of alkali-activated fly ash and slag-blended binders to organic acids was studied, and a comparison with ordinary portland cement binders was carried out. The findings demonstrate that alkali-activated binders with increased fly ash content have marginally better resistance to acetic acid, but mixes with increased slag content have better resistance to lactic acid. This is due to the solubility of the calcium and aluminum salts of acetic and lactic acids. Overall, the performance of the alkali-activated binders was better than that of the ordinary portland cement binder, with a lower mass and strength losses observed. This was attributed to their lower calcium content with less vulnerable phases, such as calcium hydroxide and ettringite. Instead, the calcium-silicate-hydrate (C-S-H) type gels in alkali-activated binders suffered decalcification and dealumination but left behind a silicon-rich gel, which helped to resist further acid attack.