Linking anisotropic chloride transport to annualised carbon intensity: A durability-informed sustainability assessment of 3D-printed UHPC

Abstract

Chloride-induced corrosion significantly shortens the service life of reinforced concrete infrastructure and increases life-cycle carbon emissions through repeated maintenance interventions. In 3D-printed ultra-high-performance concrete (3DP-UHPC), build-induced anisotropy alters chloride transport behaviour, yet its long-term durability and sustainability implications remain insufficiently quantified. This study develops a durability-informed comparative framework that links anisotropic chloride transport to maintenance-normalised carbon implications in 3DP-UHPC. Long-term immersion experiments were conducted to obtain depth-resolved chloride profiles for different build orientations. A time-dependent diffusion model incorporating surface chloride accumulation kinetics was used to identify orientation-dependent transport parameters, which were subsequently translated into corrosion-initiation-based service life and a parameterised carbon amplification formulation over a 50-year design horizon. Results show that corrosion initiation under a 20 mm cover condition is governed primarily by surface accumulation kinetics rather than instantaneous diffusion intensity. A stable durability hierarchy (3D-Z > MC ≈ 3D-Y > 3D-X) persists under realistic variations in corrosion threshold and cover depth. Within the adopted comparative framework, and using 3D-X as the reference condition, orientation optimisation yields up to a 38% relative reduction in the parameterised annualised carbon-intensity indicator without altering material composition or structural geometry. The findings indicate that build orientation can function as a non-material sustainability lever by regulating durability-controlled maintenance demand in chloride-exposed infrastructure.