The use of recycled materials in highway construction can achieve significant benefits affecting the triple bottom line (environment, prosperity, and society). Although state departments of transportation have been at the forefront of introducing recycled materials, they have been unable to clearly convey the benefits in a quantitative and transparent manner using easily understood metrics. Information on sustainability assessment characteristics—that is, energy and water consumption—is lacking. To determine the benefits of using recycled materials for six member state departments of transportation in a pooled fund, the Recycled Materials Resource Center at the University of Wisconsin–Madison was tasked with a project that would quantify the environmental and economic life-cycle benefits associated with the incorporation of recycled materials and industrial by-products in highway construction. An analysis of the environmental benefits (i.e., carbon dioxide emissions, energy consumption, and water consumption) associated with the substitution of recycled materials for conventional virgin materials in highway construction was conducted using the pavement life-cycle assessment tool for environmental and economic effects, a tool developed with the sponsorship of the Recycled Materials Resource Center. An economic impact analysis was conducted by comparing the unit prices of virgin and recycled materials. The analysis showed significant environmental and economic savings in all member states. Total environmental savings from use of recycled materials were approximately equal to the energy consumption of 110,000 U.S. households per year, 9,300 bathtubs of water, and the carbon dioxide emissions produced by 58,000 cars per year. Total systemwide economic savings from use of recycled materials was estimated to be $62.5 million.

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The conventional highway resurfacing technique of mill and overlay (M&O) partially removes the existing pavement and replaces it with asphalt derived from some recycled but mostly virgin materials. Cold-in-place recycling (CIR) is an alternative highway resurfacing method that partially mills the existing pavement and uses it beneath a thinner layer of new asphalt. CIR has become widely used for convenience and cost benefits, but the environmental impacts are poorly quantified. The objective of this study was to quantify the environmental life cycle benefits of using CIR for highway resurfacing instead of M&O. Material quantities and equipment used for CIR and what would have been used in M&O for the same project were provided by contractors for nine highway resurfacing projects in Wisconsin. With this information, a life cycle assessment (LCA) tool was used to determine the relative environmental impacts of the two methods, with energy consumption, water usage, and carbon dioxide emissions chosen as the metrics of the LCA. Results show average environmental savings of 23% in energy consumption and carbon dioxide emissions and 20% in water consumption when using CIR instead of M&O for highway resurfacing. Additionally, CIR reduced virgin aggregate consumption by 37%. Environmental savings achieved by using CIR were found to be directly related to the reduction in volume of new hot mix asphalt (HMA) used, and to the reduction in transportation of materials to and from the site. Linear correlations that can be used to estimate savings of future CIR projects were projected.