Environmental evaluation and economic analysis of fly ash-rice husk ash blended alkali-activated bricks

Abstract

This paper presents a life cycle assessment (LCA) based on environmental and economic factors of alkali-activated bricks prepared with low calcium fly ash and rice husk ash (RHA) (20% replacement of low calcium fly ash by RHA (20RHA)). The results were compared with an equivalent Portland cement (PC) concrete brick. The scope of this comparative and sensitive analysis ranges from cradle to grave. However, slightly higher impacts (5.40 kg CO2 eq/m2) were obtained for 20RHA due to the electricity generation. Manufacturing sodium silicate and sodium hydroxide are responsible for 62%–90% of the total impact for all environmental impact categories for 20RHA. An energy mix with a higher contribution of renewable energy sources in the sensitivity analysis entails favourable results, giving an approximately up to 30% reduction in blended RHA brick, while for PC bricks, less than 20% reduction was observed in most impact categories. In addition, a benefit analysis and leaching studies were conducted in order to quantify the benefits by utilizing fly ash and RHA from dumps and landfills by observing environmental credits in terms of human toxicity and fresh and marine water ecotoxicity. The 20RHA showed significant resultant benefits of 1.77 kg 1,4-DBC eq/m2 in terms of the human toxicity impact category compared with PC brick.