Life cycle assessment of fly ash, olive cake ash, and zeolite for environmentally sustainable soil stabilization

To address the environmental burden of conventional binders and improve soil geotechnical properties, pozzolanic waste materials are increasingly explored. However, a significant research gap persists in the life cycle assessment (LCA) of such materials, particularly the olive cake ash (OCA) that is readily available in Mediterranean regions, when used as a direct replacements for cement in soil stabilization. This study addresses this gap by uniquely evaluating the environmental viability of fly ash (FA), OCA, and zeolite as standalone alternatives to traditional cement for stabilizing expansive soils. A comprehensive LCA, employing the ReCiPe 2016 method and a realistic case study, was conducted, with materials dosed to achieve a target soil swelling of 5 ± 1%. FA demonstrated the best overall environmental performance, notably achieving a 93% reduction in global warming potential compared to cement under the study conditions. OCA-treated soil emerged as the second-best solution in terms of overall emissions, except in Stratospheric Ozone Depletion (SOD) and Terrestrial Ecotoxicity (TET) categories, where its emissions were higher than those of cement but still lower than those of zeolite. Cement exhibited the worst profile in 7 of 10 impact categories, while zeolite had high impacts in Marine Eutrophication (MEU), SOD, and TET. A sensitivity analysis accounting for variations in transportation distances and alternative cement production technologies validated these findings. This comparative assessment provides crucial data for advancing sustainable geotechnical engineering, highlighting the significant environmental benefits of using select waste materials as complete cement alternatives.