Durability-integrated cradle-to-cradle life cycle and cost assessment of hybrid-treated recycled aggregate concrete in central Europe

The purpose of this study is to evaluate the environmental and economic performance of hybrid-treated recycled aggregate concrete (RAC) in Germany using a cradle-to-cradle life cycle assessment (LCA) and life cycle costing (LCC) framework that explicitly integrates durability performance and end-of-life circularity. The study aims to overcome limitations of conventional cradle-to-gate assessments by adopting a durability-based functional unit that ensures functional equivalence over a 50-year service life. A performance-based functional unit of 1 m³ of concrete providing a 50-year service life under XD3 chloride exposure was applied. Six concrete systems were assessed: natural aggregate concrete (NAC), untreated RAC, polymer-impregnated RAC (PVA), cold-bond pelletized RAC, nano-silica treated RAC, and bio-cemented RAC using Sporosarcina pasteurii, with accelerated CO₂ carbonation evaluated as a sensitivity case. Region-specific German inventory data were used, including a 2024 electricity emission factor of 0.321 kg CO₂/kWh. Durability was quantified using water absorption and chloride migration coefficients, and end-of-life impacts were assessed using Module D credits. Hybrid treatments significantly improved durability, reducing water absorption from 5.5% to less than 3% and lowering chloride migration coefficients from 8.0 × 10⁻¹² m²/s to 4–6 × 10⁻¹² m²/s, enabling all treated RAC mixes to meet the 50-year service life without additional concrete cover. Untreated RAC showed limited environmental benefit once durability penalties were included (410 kg CO₂/m³), comparable to NAC (365 kg CO₂/m³ net). In contrast, polymer-treated and cold-bond pelletized RAC achieved net GWP reductions of 29% and 22%, respectively, while carbonated RAC exhibited the lowest impact (205 kg CO₂/m³, 44% below NAC). Life cycle costing results showed polymer-treated and carbonated RAC to be cost-neutral, pelletization to incur a 10–15% premium, and nano-silica and bio-cementation to be economically uncompetitive under current conditions. The study demonstrates that durability-driven, cradle-to-cradle assessment is essential for fair comparison of concrete systems. Among the evaluated options, polymer impregnation and CO₂ carbonation emerge as the most robust and immediately deployable strategies for sustainable concrete construction in Central Europe, delivering substantial environmental benefits without economic penalties.