Book Description

There is interest in determining and validating the environmental and economic benefits of incorporating recycled materials into road construction using life cycle assessments (LCA) and life cycle cost analysis (LCCA) tools. However, the process of collecting the necessary data for LCAs and LCCAs from departments of transportations (DOTs) and road construction contractors is not well defined. This thesis provides a study of real-time data collection to compare with the results of pre-construction estimated LCA data. The goal of this comparison is to determine a data collection precedent for environmental analyses of future transportation projects. Additionally, two prominent LCA tools were used in conducting the assessment and the results were compared to validate the predicted impacts. The primary body of this thesis focuses on a specific, project-based LCA and LCCA of the reconstruction and expansion of a 2.4-km (1.5-mi) stretch of the eastbound Beltline Highway in Madison, Wisconsin. Recycled materials used in this reconstruction include: fly ash, slag, recycled asphalt shingles (RAS), recycled asphalt pavement (RAP), and recycled concrete aggregate (RCA). Fly ash and slag were used as a partial replacement of cement in the ready-mix concrete. RAP was used in both hot mix asphalt (HMA) pavement as well as a base course material. RAS was substituted for binder and aggregate material in some HMA mix designs. RCA, both recycled onsite and imported, was substituted for base and subbase material. Two data collection methodologies were employed to gather the necessary inputs for the LCA of the reconstruction: 1) material quantities estimated from designs and specifications as planned prior to construction (referred as Planned), and 2) material quantities explicitly tracked and collected while construction was on-going (referred as Constructed). In the Planned data collection methodology, quantities were calculated using plan drawings and average mix designs. In the Constructed data collection methodology, key site-specific Wisconsin DOT (WisDOT) and contractor files were accessed for material quantity information. Two prominent tools were used to conduct the LCAs with the objective of validating impact results. The Pavement Life-cycle Assessment Tool for Environmental and Economic Effects (PaLATE) is an open-source LCA and LCCA program specifically developed for highway construction. Environmental outputs include energy and water consumption, carbon dioxide (CO2) emissions, and more. The second LCA tool, SimaPro, is a professional LCA software used to collect, analyze, and monitor the sustainability performance data of products and services. Some of the SimaPro impact categories used in this analysis include fossil fuel depletion, global warming, energy demand, and CO2 emissions. When comparing the LCAs of two or more products, a relative ranking of alternatives can be analyzed as well as the absolute impacts. For this study, the design of the actual roadway that incorporated recycled material (referred to as Recycled) was compared to a hypothetical design comprised of no recycled material (referred to as Virgin). In the Virgin design, recycled material quantities were replaced with equivalent virgin materials. This method demonstrates the impact reductions from the use of recycled material. To validate the LCA results, impacts predicted by PaLATE versus SimaPro were compared, with the primary focus on the common impact categories of energy and CO2 emissions. Results show that the material quantities obtained from the two data collection methods are within one order of magnitude for all categories, demonstrating general agreement regardless of Constructed or Planned data. Generally, the Constructed data predicts slightly greater (1.2x to 2.2x) material use as compared to the Planned data. Impact reductions were seen in all PaLATE categories from the use of recycled materials, regardless of data collection methodology. However, most impact categories saw greater reductions using the Planned data as compared to the Constructed data. The greater reductions are due to a greater ratio of recycled to virgin material use in the quantities found by using the Planned data collection method. A comparison of absolute impact predictions, rather than reductions, revealed that the Planned data quantities saw lower impacts than the Constructed data. The Constructed data quantities have greater absolute impacts because this collection methodology found that more materials were used overall than as predicted by the Planned data collection method. Similar results are seen for the SimaPro analysis, but in different environmental impact categories. Overall, the Planned and Constructed data produced relatively comparable results. In the particularly relevant categories of energy and CO2 emissions, the two data sets' results had a difference of only 7-8% according to the PaLATE analysis. In SimaPro’s global warming and fossil fuel depletion categories, the Constructed data results predicted a 5-6% difference from the Planned data impacts reductions. When validating the impacts across PaLATE and SimaPro, the predictions from both tools for energy and CO2 emissions appear to have minor variability (within 10%). The trends explored in this thesis indicate that the data collection methodology and resulting LCA inputs have a greater influence in environmental impact predictions as compared to the analysis tools, particularly for energy and CO2 emissions. Additionally, an LCCA was conducted using a simple cost-savings based on material unit prices. To calculate the savings, the cost for a recycled material was compared to the cost for an equivalent virgin material (e.g. fly ash vs. cement). Planned data lifetime savings for the project were estimated at approximately $209,800, while the Constructed data predicted a lifetime savings of $267,000. In general, the Constructed data quantities resulted in more cost savings because more recycled materials quantities were found by this collection methodology. The grand total savings differ by approximately $57,000. While this may seem like a small number compared to typical DOT budgets, it becomes significant when considering the savings are for only 3 lane-miles. This stresses why explicit tracking may be important to accurately determine cost reductions from recycled material use. Based on the LCAs and LCCA, similar economic and environmental impacts and reductions were predicted using the two data collection methodologies. However, the Constructed data collection was able to capture more accurate material quantities, as well as a greater variety of material types and mix designs. Although this in-depth tracking of material may have resulted in more accurate life cycle impact predictions, the Planned data quantities resulted in similar enough impacts to suggest that this methodology could be an acceptable method for estimating future LCA inputs. Additionally, based on comparable impact assessment parameters, the two LCA software tools provided similar results in terms of energy use and CO2 emissions. Therefore, DOTs should attempt to focus future efforts on material tracking for the purpose of LCAs and LCCAs when these issues are critical. Additional studies are included in Appendix A and B. Appendix A discusses a case study conducted prior to the analysis included in the main thesis. For the Appendix A study, data was collected post-construction from designs and plans, i.e. data was not explicitly tracked. The assumptions and concerns generated by this first case study prompted the data collection methodology research question posed by the main thesis. Appendix B includes a report on the development of an environmental impact tool used to assess the sustainable management of pavements in poor condition. For this impact tool, different rehabilitation and management methods are analyzed for economic and environmental costs. The environmental impact of each management strategy was calculated using LCAs, and the results were incorporated in a more in-depth evaluation tool. This paper demonstrates an application of road-related LCAs that differs from the two case studies.