Modeling the substitution of natural materials with industrial byproducts in green roofs using life cycle assessments

This study conducted life cycle assessments (LCAs)on four types of extensive green roofs and involved replacing natural perlite with the byproducts coal bottom ash (CBA)and fly ash-based aggregates (FAAs)in both the substrate and drainage layers of green roofs. The following combinations were investigated: perlite in both the substrate and drainage layers (Perlite_SUB-Perlite_DRIN), perlite in the substrate layer and FAAs in the drainage layer (Perlite_SUB-FAA_DRIN), CBA in the substrate layer and perlite in the drainage layer (CBA_SUB-Perlite_DRIN), and CBA in the substrate layer and FAAs in the drainage layer (CBA_SUB-FAA_DRIN). Two types of allocation approaches including mass allocation and system expansion were applied to the byproducts. The LCAs encompassed the production stage and the end-of-life stage. A two-stage analysis of variance (ANOVA)was used to analyze the ReCiPe results and the following was confirmed: (i)the analysis identified the best environmentally friendly roof alternative, (ii)it was observed that the results from the simplification of the LCA for the roof (omitting the end-of-life stage)depended on the type of evaluation approach used in the LCA, and (iii)the more comprehensive performance of the LCAs of green roofs was associated with a combination of the ReCiPe and ANOVA methodologies.