Transforming almond shell waste into high-value activators for low-carbon concrete: life cycle assessment and technoeconomic analysis

Low-carbon concrete, including through the use of alkali-activated binders (AABs), is being developed globally to meet construction industry decarbonization goals by reducing reliance on Portland cement (PC). However, the cost and environmental impacts of the alkaline resources conventionally used in AABs are among the factors that have hindered their application. Here, life-cycle assessment (scope A1-A3) and technoeconomic methodologies were used to quantify the GHG and air pollutant emissions as well as the costs of a biogenic alkali resource from almond shell ash for AAB mortars. The results demonstrate that AAB mortars with 50 % and 100 % almond ash replacement of synthetic chemical-alkali resources levels result in an improved combination of GHG emissions and compressive strength than PC mortar. Findings show that almond ash AABs can result in 8 %–56 % lower GHG emissions, and the emissions of nitrogen oxide (NO X ), sulfur oxide (SO X ), and particular matter less than 10 μm (PM10) are up to 49 %, 62 %, and 53 %, lower than the synthetic chemical-based AAB mortars, respectively. The results demonstrate that AAB mortars with 50 % and 100 % almond ash replacement of synthetic chemical-alkali resources levels result in an improved combination of GHG emissions and compressive strength than PC mortar. When findings are scaled based on resource availability in California, the analysis indicates that 0.08 to 0.47 million metric tons of GHG emissions could be avoided for concrete production in the state if almond shell ash binders are used instead of chemical-based alkali-activated. These findings suggest that using almond shell ash in almond-growing regions could support environmental impact mitigation strategies while maintaining desirable concrete strength performance. • Almond shell ash mixtures have lower GHG and air pollutants than chemical AABs. • 50 % and 100 % AABs have lower GHG emissions to compressive strength ratios. • Up to 0.47 million metric tons of GHG emissions could be avoided in California. • Transportation costs of GGBFS and materials costs of chemicals increase AABs costs.