Life Cycle Assessment of Asphalt Roads : Decision Support at the Project Level
Sammanfattning: Transport infrastructures such as roads are assets for the society as they not only ensure mobility but also strengthen society’s economy. Considerable amount of energy and materials, that include bitumen, aggregates and asphalt, are required to build and maintain roads. Improper utilization of energy and/or use of materials may lead to more waste and higher costs. The impact on the environment cannot be neglected either. Life cycle assessment (LCA) as a method can be used to assess the environmental impacts of a road system over its entire life time. Studying the life cycle perspective of roads can help us improve the technology in order to achieve a system that has a lower impact on the environment. There are number of LCA tools available. However, implementation of such tools is still unseen in real road projects. This clearly indicates that there are gaps which are needed to be filled in order to bring these tools into practice. An open road LCA framework was developed for the asphalt roads in order to help in decision support at the late project planning stage such as that related to the green procurement. The framework takes into account the construction, maintenance and end of life phases and focuses on energy and greenhouse gas (GHG) emissions. Threshold values for the production of some additives were also determined to show how LCA tools can help material suppliers to improve the road materials production processes and the road authorities to set limits on the use of different materials based on the environmental criteria. Additive consideration and feedstock energy in road LCAs were also identified as gaps that were looked in detail. The attributes that are important to consider in an asphalt road LCA that seeks to serve as a decision support in a procurement situation are described.A brief literature review was carried out that focused on project LCAs, and specifically those considering pavements, as this level is assumed to be appropriate for questions relevant in a procurement situation. Following the different standards; road LCAs developed all over the world have generated a lot of knowledge and the studies have been different from each other such as in terms of goals and system boundaries. Hence, the patterns observed have been very different from study to study. It was also difficult to assess the decision support level for which the various LCA frameworks or tools were developed. It is important to define system boundaries based on where in the system the decision support is needed. For LCA to be useful for decision support in a procurement situation, it is important to have a clear understanding of the attributes that constitute the life cycle phases and how data of high quality for them are obtained. The level of consistency and transparency of road LCAs becomes increasingly important in pre-procurement and procurement situations. The key attributes used in a road LCA should mirror the material properties used in a pavement design and therefore be closely linked to the performance of the road in its life cycle.From the different case studies, it was found that asphalt production and transportation of materials are usually highest in the energy and GHG emissions chain. It is highly favorable to have the quarry site, the asphalt plant and the construction site not far from each other and to use the electricity that has been produced in an efficient way. Based on the laboratory test results, it is shown that the effects of chemical warm mix asphalt additives (WMAA)s must be evaluated on a case by case basis since WMAA interaction with the aggregate surface mineralogy appears to play a significant role and thus affects its long term structural behavior. Using the material properties obtained from the Superpave indirect tensile test (IDT) results, pavement thickness design was done in which Arlanda aggregate based asphalt mixtures resulted in thinner pavements as compared to Skärlunda aggregate based asphalt mixtures for the same design life period. Energy (feedstock and expended) saving and reduction in GHG emissions were also seen with addition of WMAA, for both aggregate type cases, based on the data used. Importantly, the results presented illustrate the importance of a systems based LCA approach for evaluating the sustainability for different design and construction options. In this context, having actual pavement material properties as the key attributes in the LCA enables a pavement focused assessment of environmental costs associated with different design options.
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