Life cycle assessment of recycled aggregate concrete on its environmental impacts: A critical review

Recycled aggregate concrete (RAC) is expected to a sustainable solution to alter the virgin aggregate concrete (VAC) in structural use. While it is able to address environmental issues for both virgin aggregate (VA) consumption and waste generation, not so many studies quantify the environmental burdens through life cycle assessment (LCA). RAC is a composite material, which LCA should be analysed by considering its mixtures, and corresponding production technologies. This aggravates the complexity of LCA model since it involves great numbers of unit processes. Through reviewing 90 articles, this paper overviews the developments of LCA for RAC, and identifies the research trend shifts with the promotion of RAC technology. Although many relevant studies have become more comprehensive, there are still numerous inconsistencies and uncertainties existing in LCA processes that avoid LCA results from comparisons. From the review, it clearly points out that results are greatly affected by two aspects that are mix design and LCA mechanism. Cement production has the predominant contribution to the environmental impacts of concrete, and normally followed by transportation process. Accordingly, mix design, together with treatment technology of raw materials, influence the overall environmental performance of concrete. With respect to LCA phases, selections of FU, system boundary, allocation rule, LCI and LCIA methodology are highly subjective, causing more uncertainties that hinder the comparisons across the studies. It is therefore suggested that variations of mix design and inconsistencies from LCA mechanism could be explored further in the field of RAC to establish the holistic and multi-criteria study for comparison and decision making.