Construction Materials from Stainless Steel Slags: Technical Aspects, Environmental Benefits, and Economic Opportunities

State-of-the-art technologies that implement theindustrial ecology concept only make it to the market if environmental gains and economic benefits are significant. Therefore, the article investigates, in an interdisciplinary way, two innovative technologies that valorize stainless steel (SS) slags as block masonry (bricks): carbonation and thermo-alkali-activation. The technical, environmental, and economic features of three SS brickssolid bricks, perforated bricks, and lightweight aerated blocksare compared to commercially available construction materials. Although the produced bricks meet industrial standards, technical challenges, such as optimization of alkali addition and use of metal molds, should be dealt with before upscaling to industrial production. A cradle-to-gate life cycle assessment that aggregates the results of the various impact categories shows that the environmental impact of solid and perforated SS bricks is lower than the impact of conventional clay-baked bricks owing to the avoidance of additives for slag stabilization and energy consumption for sintering clay. The impact of aerated SS bricks was found to be similar to the commercially available aerated blocks. More specifically, the carbon dioxide uptake from carbonation reduces the overall environmental impact, whereas use of alkalis increases the impact. A strengths weaknesses opportunity threats analysis highlights the economic advantages of SS bricks originating from lower energy requirements, reduced dependence on primary resources, and improved metal recovery from slag. However, in order to apply the innovative technologies at industrial scale, challenges related to processing conditions, feedstock variability, and potential competition from existing brick suppliers have to be overcome.