Structural Design, Environmental Impacts and Life-Cycle Costs of Alternative Cast-in-Place Motorway Tunnel Linings in the San Donato Case Study

This study compares conventional steel-reinforced concrete (RC), glass fibre-reinforced polymer (GFRP)-reinforced concrete and hybrid GFRP–steel fibre-reinforced concrete (HYB) for the permanent lining of the New San Donato motorway tunnel, Italy. Structural design is integrated with life-cycle assessment and partial life-cycle costing over 100 years. The base scenario includes construction and one major repair at year 50 for each solution, replacing approximately 13,000 m3 of concrete. Relative to RC, GFRP and HYB reduce maintenance global warming potential by 5.76% and 9.90%, respectively. Construction-plus-maintenance impacts are approximately 33,100, 32,997 and 34,092 t CO2-equivalent, indicating comparable cumulative climate performance for GFRP and RC and higher impacts for HYB. Undiscounted costs are EUR 72.23, 67.03 and 69.46 million, respectively. GFRP remains the least expensive solution across real discount rates of 0–6%. Timing sensitivity identifies year 37 as the latest whole-year RC repair for which both alternatives have lower present costs throughout this interval, retaining their repairs at year 50. These findings highlight the potential economic value of delayed maintenance. Intervention timing remains scenario-based: material-specific degradation is not modelled, and potential selective-demolition benefits are excluded from the numerical assessment.