Environmental Benefits of Cold-in-Place Recycling

Abstract

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.