Carbon footprint discrepancy between design and construction phases in maritime engineering projects: A case study of land reclamation at the port of Taipei

Global commitments to carbon neutrality have heightened the focus on greenhouse gas emissions from infrastructure projects. Land reclamation, extensively used to expand port capacity in coastal regions, requires large‑scale earthworks, substantial material use, and intensive heavy equipment operation, all of which generate considerable carbon emissions. However, design‑phase estimates of these emissions typically differ from construction-phase emissions because of uncertainties in field conditions and variations in material reuse efficiency. This study applies a partial life cycle assessment with a cradle‑to‑construction boundary to quantify and compare design‑ and construction‑phase emissions for a land reclamation project at the Port of Taipei, Taiwan. Using bills of quantities, construction records, and emission factors from Taiwan’s Ministry of Environment database, the design‑ and construction-phase emissions were calculated as 12,874,621 and 13,521,035 kg CO2e, respectively, indicating an underestimation of 4.78% at the design stage. The primary causes of this discrepancy were differences in dredging quantities, marine equipment operating time, and higher‑than‑assumed recovery rates of reusable materials. The recycling of existing concrete blocks and revetment rocks led to substantial carbon savings; each reused concrete block embodied approximately 684 kg CO2e, compared with approximately 7250 kg CO2e for a newly manufactured block. The results demonstrate that quantity variation and on‑site uncertainties are the dominant drivers of the emission discrepancies, whereas design‑phase unit‑rate estimates remain sufficiently accurate for preliminary carbon assessments. This case study provides project‑level evidence for refining carbon accounting practices in maritime infrastructure and supports the integration of material reuse and waste minimization strategies into early‑stage port planning.