Effect of transportation of fly ash: Life cycle assessment and life cycle cost analysis of concrete

Abstract

The incorporation of fly ash into concrete may be limited by its quality, local availability, and additional cost incurred due to transportation. The specific objectives of this study are to: conduct an experimental program to evaluate the material properties for the four concrete mix designs considered for analysis (100GU, 25FA, 35FA, 50FA); identify environmental impact categories that are most greatly affected by material transportation; develop a life cycle assessment (LCA) model and a life cycle cost (LCC) model to respectively quantify the environmental and economic benefits and/or burdens that reflect the interplay between concrete mix designs and transportation of fly ash (up to 1000 km by truck). This analysis considers a study period of 100 years and is based on the proposed repair schedule. This study defines the ‘break-even distance’ as the maximum distance at which the LCA or LCC analysis results (i.e. environmental impact or cost) for concrete containing fly ash is lower than corresponding results for the 100GU concrete. Key outcomes of this study are: (i) ‘ecotoxicity’, ‘human toxicity (non-cancer)’, and ‘resources and fossil fuels’ are the most highly affected environmental impact categories by transportation of fly ash. In contrast, global warming potential was minimally affected. (ii) The break-even distance depends on the time to first repair (TFR), total volume of concrete required over 100 years of being in service and the percentage of cement replacement by fly ash. For both the LCA and LCC analysis, the concrete mix, 35FA, has the lowest break-even distance compared to the 25FA and 50FA. The fly ash mix designs ranked in order of least to most environmentally friendly and economically viable are: 35FA, 25FA, and 50FA. (iii) The break-even distances are longer for the LCC analysis compared to the LCA model results which indicates that the environmental impacts associated with the transportation of fly ash are more severe than the cost associated with the process, based on the analysis and assumptions in this study.