Development and Validation of Low-Carbon Concrete for Floating Offshore Wind Substructures

This study investigates the development, optimisation and preliminary scale-up assessment of low-carbon self-compacting concrete mixes tailored for floating offshore wind substructures, comparing traditional Portland cement (CEM I) with slag-based CEM III/B binder systems. A comprehensive experimental programme was conducted, encompassing multiple laboratory-scale mix designs, fatigue behaviour assessment using the Locati method, and pilot-scale production trials involving one 1.5 m 3 batch of each selected mix. Fresh properties confirmed self-compacting performance at laboratory scale. Mechanical performance at 28 days demonstrated high compressive strength (≈ 75–85 MPa) and elastic modulus (≈ 45–52 GPa) for both binder families, while durability indicators showed significantly lower chloride migration coefficients for CEM III/B concrete mixes (≈ 1.5–2.6 × 10⁻ 12 m 2 /s vs. ≈ 1 × 10⁻ 11 m 2 /s). Preliminary fatigue tests indicated comparable responses for both binder systems, with slag-based concrete mixes mobilising a slightly higher proportion of static strength. The pilot-scale trials showed generally consistent mechanical and durability-related properties between laboratory and plant production. Slag-based concrete mixes also exhibited substantial reductions in material cost (≈ 10–15%) and A1–A3 material-level embodied carbon (≈ 50%), with carbon efficiency nearly doubled when normalised by strength. Overall, the results demonstrate the strong potential of CEM III/B concrete as a technically competitive and lower-carbon alternative to CEM I for offshore structural applications.