Assessment of carbon emissions and life cycle cost in railway infrastructure: comparison between steel slag ballast and natural aggregate

This paper evaluates the use of steel slag aggregates (SSA) as ballast for railways, from environmental and financial perspectives. The environmental assessment employs the Life Cycle Assessment (LCA) methodology framework to compare steel slag ballast (SSB) with natural aggregate ballast. The study focuses on the Global Warming Potential (GWP) impact category (also known as carbon footprint), measured in kg of CO 2 equivalent. The study considers a functional unit of 1 km of railway track over an 8-year reference service period, from a case study in the Southeast region of Brazil. The CO 2 uptake through the natural carbonation of the SSA was obtained through thermogravimetric analysis, resulting in an estimated uptake of 17.7 kg CO 2 /t SSA under the conditions considered, a value that was incorporated into the assessment. In addition to the environmental assessment, a Life Cycle Cost (LCC) analysis was conducted to evaluate the economic performance of the railway ballast alternatives over their life cycle. Within the defined system boundaries, the results showed that the railway with steel slag ballast showed a lower GWP than conventional ballast, primarily due to the estimated CO 2 uptake during natural carbonation. For the same 8-year reference service period, we calculated −4.82E+04 kgCO 2 e for the SSB (thus absorbing CO 2 ) and 1.30E+04 kgCO 2 e for the conventional ballast. A sensitivity analysis indicated that the SSB maintains its environmental advantage even with transportation distances of up to 470 km. From a financial standpoint, the LCC of the railway with SSB was 32% lower than that of conventional ballast. The study confirms the potential of SSB as an environmental and financial alternative for railway ballast, given the premises adopted in this research.