Environmental impact assessment of alkali-activated mortar with waste precursors and activators

Abstract

Synthetic activators used in alkali-activated binder are the primary contributors to its adverse environmental effects. Therefore, this study aims to perform a life cycle assessment of alkali-activated mortar (AAM) prepared from industrial waste as precursors and activators. The impact analysis is performed through ReCiPe methodology for six different AAM mixes. Environmental impacts of replacing conventional precursors (fly ash and slag) with waste ceramic powder (WCP) and red mud (RM) and conventional activators (sodium silicate (SS) and sodium hydroxide (SH)) with RM, desulfurization dust, and silica fume are assessed. The efficiency of ReCiPe is compared with recommendations from the International Reference Life Cycle Data System. Sensitivity analysis for SH produced using three different techniques and simplified cost analysis for the mortar mixes is conducted. SS is observed to contribute 50–59% of climate change for mixes with conventional activator combination. WCP as a precursor warrants higher dosage of SS and SH, thereby increasing the environmental impact. Replacing SS with silica fume has the least negative effects on ecosystem quality and human health. AAM prepared with conventional activators shows lower resource depletion due to a lower dosage of activators and the absence of pretreatment of fly ash. ReCiPe can be used to evaluate all the impact categories except freshwater ecotoxicity and human toxicity, for which USEtox is suggested. Sensitivity analysis shows that the membrane cell process of SH production is eco-efficient. Savings of up to 14% are observed by replacing both precursors and activators with industrial residues.