Environmental and economic perspective of waste-derived activators on alkali-activated mortars

Abstract

Alkali-activated binders have been considered a low carbon alternative to cement and are produced by reacting aluminosilicate precursor with an alkali-activator. However, alkali-activators have been observed to be a major contributor to the environmental burdens of alkali-activated materials regarding various environmental impact categories. Therefore, this study aims to perform an environmental impact assessment using life cycle assessment methodology on alkali-activated mortars produced from chemically modified one- and two-part waste-derived activators (waste glass and rice husk ash) in comparison to conventional one- and two-part alkali-activated mortars, to estimate the influence of activator on environmental impact of mortar. Additionally, a simplified cost analysis of the different mortar compositions was conducted. A sensitivity analysis was performed on the key parameters, and allocating emissions to waste glass and rice husk ash. Results show that waste glass and rice husk ash-derived alkali-activated mortar resulted in up to 62%, 61%, 76% and 56% reduced emission respectively in climate change, fossil depletion, terrestrial acidification and photochemical ozone creation formation when compared to conventional alkali-activated mortar counterpart. Sensitivity analysis indicated that waste glass and rice husk ash are not so sensitive to mass allocation, with a maximum of 5% increased emissions observed in the above-mentioned impact categories. Additionally, sensitivity analysis on sodium hydroxide demonstrated that production from chlorine-alkali electrolysis using technology-mix produced improved environmental performance in comparison to production from brine solution and diaphragm route, respectively. Sensitivity analysis on sodium silicate using an alternative inventory data indicated the emissions can increase regarding one-part or decrease regarding two-part alkali-activated mortars. Results from cost analysis indicated up to 19% cost savings from waste-derived alkali-activated mortar compared to conventional alkali-activated mortar. In conclusion, chemically modified waste-derived activators are a promising alternative in improving environmental performance of alkali-activated materials if their usage also reduces or substitutes the need for conventional alkali-activators.