Development of environmental impact tool to assess the sustainable management of pavements in poor condition

Abstract

In 2014, the Minnesota Department of Transportation (MnDOT) developed a project to analyze the performance, service life, costs, and environmental impact of nine treatment strategies for increasing the sustainability of pavements in poor conditions on Minnesotan roadways. MnDOT’s goal was to develop a spreadsheet decision tool for selecting an appropriate treatment for pavements with different physical and operational characteristics. The Recycled Materials Resource Center (RMRC) was tasked with the environmental analysis, and performed a life cycle analysis (LCA) of the nine treatment options using the Pavement Life-cycle Assessment Tool for Environmental and Economic Effects (PaLATE). The treatments addressed initial roadway conditions and incorporated both new and recycled materials. Treatments included entire surface, areal applications (chip seal, double chip seal, micro-surfacing, CapeSeal, UltraThin bonded wear course, 5-cm hot mix asphalt (HMA) overlay, and mill & 5-cm HMA overlay) and localized applications (mastic for patching and crack sealing). PaLATE assesses the environmental impacts of pavement and road construction based on user inputs of initial design dimensions, initial construction material and processes, maintenance, equipment use, and transportation. In this analysis, four environmental factors output by PaLATE were considered to assess the treatments sustainability: Energy, water consumption, CO2 emissions, and RCRA hazardous waste. Roadway lifetimes depended on the type of treatment and the initial severity of the roadway’s condition. To account for differing treatment lifetimes, the results were annualized. In general, the magnitude of the environmental impact was proportional to the amount of material required. The localized treatments (mastic patches and crack sealing) required far less material then the areal treatments, thus had a smaller environmental impacts. The 5-cm HMA overlay and mill & 5-cm HMA overlay required the most material, thus had the greatest environmental impacts. Of the areal applications the chip seal and micro-surfacing had the smallest environmental impacts.