Calculation of the environmental impact of the integration of industrial waste in concrete using LCA

The production of concrete, the most used building material globally, is causing severe environmental damage. This is known to be primarily attributed to the production of ordinary Portland cement (OPC). Hence, a vast effort is directed within the concrete industry to find alternatives that would yield a more sustainable concrete product. Concurrently, industrial waste materials (IWM) are increasing in volume and, without a clear valorization path, are mostly wasted in landfills. Although several IWM were researched to determine the possibility of use in concrete, only fly ash (FA), ground granulated blast furnace slag (GGBS) and silica fume (SF) are industrially proven to be effective thus far. Therefore, the aim of this chapter is to assess, through life cycle assessment (LCA), the environmental impacts of producing concrete binders with partial or total replacement of OPC with one or more of the most common IWM.

Although the principle of integrating an IWM as replacement of a material with a significant environmental impact such as OPC seems promising, this chapter showed that some measures are needed to ensure the reliability of the performed LCA study. First of all, the surveyed literature emphasized that the appropriate scope of an LCA study of a concrete product integrating FA, GGBS, or SF is cradle-to-grave. Secondly, the inventory data for the LCA study should be based on an extensive database of secondary data or primary site-specific one. Thus, a database presented by the authors of this study provided an example of a reliable inventory data source. The final criterion that differentiates the LCA methodology when incorporating IWM is the significance of including the impact of transporting the material from the landfill to the concrete batch plant as well as including the impact allocation from previous recycling processes. In this chapter, a case study was prepared using the average values of the inventory data of FA, GGBS, and SF in an LCA, and the environmental impacts of each were compared against OPC. The results show that, per unit mass, only FA actually achieves an environmental saving compared to OPC. However, it is important to highlight that there is an expected decrease in the availability of FA internationally due to the trend of closing down coal-powered electric power plants. Finally, a sensitivity analysis was prepared to highlight the contribution of the amount of allocated impacts from the original processes of IWM production that showed that all three materials would have a lower environmental impact than OPC for an impacts' allocation lower than 1%.