In the development of low-emission concretes the focus has been on the reduction of carbon footprint by using supplementary cementitious materials (SCMs). However, the resistance against chloride ingress may vary considerably among the different types of SCM concretes. For concrete structures exposed to chloride-induced corrosion, the resistance against chloride penetration is decisive in determining the service life of the structures. This paper presents calculations of CO2 emissions (Global Warming Potentials—GWPs) from two road culvert solutions, a concrete culvert with two types of low-carbon concretes and a steel pipe culvert. It was found that the main source of the emissions came from the production of concrete and steel materials. The importance of including service life as a parameter in the assessment of CO2 emissions from concrete infrastructures is demonstrated through the chloride ingress simulations of four different SCM concretes. Based on Fick’s second law of diffusion, the service life for a reinforced concrete structure can be twice as long by using concrete with 20% fly ash and 4% silica fume than by using concrete with 35% fly ash. The GWP from concrete is typically given per volume unit. However, a more appropriate unit for LCA of concrete infrastructure should be to include service life and strength parameters in the GWP calculations.