Assessing technological properties and environmental impact of fired bricks made by partially adding bottom ash from an industrial approach

Over the past few decades, the fired clay brick industry has searched for industrial wastes to substitute raw clay deposits and lessen their impact on the environment. Despite several investigations showing positive results, industrial applicability is still scarce, mainly due to differences between industrial and laboratory procedures and the usage of certain wastes that already have added value in other circular economy chains. In addition, the assessment of such proposals commonly misses the environmental impact issue which is merely assumed to be positive. For these reasons this study, for the first time, has assessed together technological properties and the environmental impact of bricks made by strictly following industrial procedures. Hence, biomass bottom ash (BBA) was added at 9 replacement ratios, ranging from 2.5 to wt. 20.0% for making extruded bricks subjected to industrial drying and firing curves. Physical, thermal and mechanical properties of fired products were properly assessed and compared with the requirements set forth by Chilean standards. In addition, a life cycle impact assessment was developed to compare the ecological footprint among series. Although mechanical and water-proof requirements may limit the replacement ratio for exposed bricks, the feasibility of using BBA at industrial scale has been successfully demonstrated. Regarding the environmental impact, the raw clay may be replaced without adversely causing toxicity levels to exceed mandatory limits. However, this study demonstrated that the incorporation of BBA increases CO2 emissions due to the decomposition of contained carbonates during the firing process which compromise the results in terms of global warming potential and water consumption which highly impact on human health and ecosystems quality.