This paper assesses the impact of climate change on the novel repair of Ferrycarrig Bridge, a reinforced concrete (RC) marine bridge on Ireland's southeast coast. Five unique repair solutions were applied to the seven crosshead beams on Ferrycarrig Bridge during works in 2007. The two solutions under examination herein involved replacement of the concrete around the sides of the crosshead beams with either 100% Ordinary Portland Cement (OPC) concrete or concrete in which 60% of the cement was made up of Ground Granulated Blast Furnace Slag (GGBS) and 40% OPC. Changes to environmental policy mean that the use of GGBS within RC structures is becoming increasingly popular. Thus, understanding its performance over time is imperative. Chloride ingress and concrete crack modelling are completed herein to compare how climate change will affect the service life of the crosshead beams in which the OPC and OPC+GGBS concrete solutions are applied. The results stemming from this modelling are used to quantify the impact of reinforcement corrosion and concrete deterioration on the crosshead beams' structural capacity. The findings indicate that without consideration of climate change, the OPC+GGBS concrete solution utilised in Ferrycarrig Bridge is 4.75 times more resistant to severe cracking caused by chloride-induced reinforcement corrosion than the OPC concrete solution. However, the durability of the OPC+GGBS concrete is more adversely affected by climate change with a lifetime reduction of 15.8% for the worst climate scenario as compared with a reduction of just 2.7% for the OPC concrete, reducing relative merit from 4.75 to 4.11.