When is carbonation-cured concrete actually cleaner? A systematic review, a net-benefit condition framework, and a proposed minimum reporting set for CO2 mineralization in cement-based products

Cement manufacture releases 7–8% of global anthropogenic CO 2 , most of it from the irreducible calcination of limestone. Accelerated carbonation curing mineralizes captured CO 2 inside cement-based products. Whether it delivers a net climate benefit, and under what conditions, cannot presently be answered from the published life-cycle assessment (LCA) literature. A reproducible PRISMA 2020 search (713 records), confirmed against Web of Science, identified seventeen studies declaring a functional unit, a cradle-to-gate boundary and a non-carbonated comparator. Their outcomes cannot be pooled: five functional-unit bases, seventeen comparators, baselines spanning 280–540 kg CO 2 -eq/m 3 , and results reported in structurally different forms. That incommensurability is the first finding. In most of the set the benefit tracks avoided Portland clinker rather than mineralized CO 2 : every reduction above 10% involves clinker being substituted or eliminated, and one study reports 5–8 kg CO 2 -eq per tonne of cement for each 1% of clinker replaced. Across matched comparisons the isolated effect of carbonation spans both signs — from a 3.1–11.3% net increase once process electricity is charged to reductions of 37%. Varying only the CO 2 recovery route for one product returns 68%, 77% and 71%. Of twenty-five papers reporting an environmental result, eight omit a functional unit or system boundary. A net-benefit condition model accounts for the spread, and a five-field minimum reporting set mapped to EN 15804, ISO 21930 and ISO 14025 is proposed so future LCAs can be synthesized.