Stephen T Muench

Assessing Potential for Warm-Mix Asphalt Technology Adoption

Warm-mix asphalt (WMA) describes a range of technologies that seek to lower emissions and reduce energy consumption by lowering the temperature at which asphalt mixtures are produced and placed. Despite these benefits, reduced mixture viscosity may be the most likely reason for widespread adoption of WMA technologies. Hot-mix asphalt (HMA) producers are unlikely to adopt WMA technologies solely to lower emissions, because current environmental regulations and the relatively clean nature of HMA plants make lower emissions unnecessary and unprofitable except in select air pollution areas. Producers are also unlikely to adopt WMA technologies solely to reduce energy consumption, because energy savings are less than the associated costs except in the most expensive energy markets. Reduced viscosity makes the best business case for widespread WMA technology adoption, because this benefit offers cost and risk reduction: it can (a) alleviate compaction problems associated with cool weather, (b) reduce compaction equipment needs at the job site, and (c) lower the risk of poor compaction when working with stiff mixtures. This conclusion is supported by basic economic calculations, a survey of the Icelandic pavement industry showing strong support for WMA technology use to improve cool weather paving, and two projects in Maryland showing the potential for WMA technology use to lower the risk of poor compaction of high reclaimed asphalt-pavement mixtures.

Roadway Construction Sustainability Impacts: Review of Life-Cycle Assessments

Each year the United States places about

Life-Cycle Assessment of Reconstruction Options for Interstate Highway Pavement in Seattle, Washington

100 billion of roadway construction. This level of activity suggests possibly significant sustainability implications in the construction activities for this work. One means to quantify some of these impacts is through life-cycle assessment (LCA). A review of 14 roadway construction LCA papers reveals some common ideas about the ecological impacts of roadway construction. Some key observations are that (a) the energy expended during roadway construction is roughly equivalent to that used by traffic operating on the facility for 1 or 2 years, (b) total energy use during roadway construction varies but is typically on the order of 3 to 7 TJ/lane mile, (c) total CO2 emissions during roadway construction vary but are typically 200 to 600 Mg/lane mile, (d) materials production makes up 60% to 80% of energy use and 60% to 90% of CO2 emissions associated with construction, (e) construction activities at the jobsite make up less than 5% of energy use and CO2 emissions, and (f) transportation associated with construction makes up 10% to 30% of energy use and about 10% of CO2 emissions associated with construction.

Calibration of NCHRP 1-37A Software for the Washington State Department of Transportation: Rigid Pavement Portion

Life-cycle assessment (LCA) is a tool that can be used to identify the environmental impact of a product or process. This paper compares three replacement options for an aging portland cement concrete (PCC) pavement with the use of an LCA process-based protocol. The options are to remove and replace the aging pavement with PCC pavement; remove the aging pavement and replace it with hot-mix asphalt (HMA) pavement; and crack and seat the existing pavement and then place an HMA overlay. Each option investigated includes a detailed construction and rehabilitation schedule and is analyzed over 50 years. The results show that materials production (e.g., cement, asphalt, PCC, and HMA) dominates the energy use, emissions, and impacts for all three options. In general, HMA production tends to cause the HMA option to have the highest energy use, whereas cement production tends to cause the PCC option to have the highest global warming potential (GWP). The crack, seat, and overlay option was the lowest energy user, had the lowest GWP, and produced the least emissions in more categories measured than the other two options. This may become a strong argument for expansion of the crack, seat, and overlay method of rehabilitation.

Construction-Related Temperature Differentials in Asphalt Concrete Pavement: Identification and Assessment

A significant amount of Washington State Department of Transportation (WSDOT) portland cement concrete (PCC) pavement that was placed in the 1960s is nearing the end of its serviceable life and must soon be rehabilitated or replaced. Initial WSDOT estimates place the cost of the anticipated work at more than

Bituminous Surface Treatment Protocol for the Washington State Department of Transportation

600 million. A tool to predict PCC pavement deterioration and ultimate failure is needed to prioritize rehabilitation and reconstruction efforts best. The software associated with NCHRP Project 1-37A was chosen as a promising tool worthy of assessment for this application. The urgency of the situation necessitated its use, despite the lack of formal calibration guidance, some software bugs, and isolated model inconsistencies. A procedure was developed and used to calibrate the rigid pavement portion of the NCHRP 1-37A software to data obtained from the Washington State Pavement Management System (WSPMS). Significant findings resulted: (a) the rigid pavement portion of the software was calibrated succ...

Sustainability Trends Measured by the Greenroads Rating System

Numerous Washington State Department of Transportation (WSDOT) paving projects have experienced a cyclic occurrence of premature failure of open-textured asphalt concrete (AC) pavement sections by fatigue cracking, raveling, or both, generally called “cyclic segregation” or “endof-load segregation.” This resulted in an initial study in which mat temperature differentials were observed during laydown. In turn, this led to the current study and the reported results. Pavement temperature differentials result from placement of a cooler portion of the hot-mix mass into the mat. This cooler mass generally constitutes the crust, which can develop during hot-mix transport from the mixing plant to the job site. Placement of this cooler hot mix can create pavement areas near cessation temperature that tend to resist proper compaction (they may also exhibit tearing or roughness or appear to be open textured). These areas were observed to have decreased densities and a higher percentage of air voids (higher air voids). Four 1998 WSDOT paving projects were examined to determine the existence and extent of mat temperature differentials and associated material characteristics. An infrared camera was used to identify cooler portions of the mat, which were then sampled along with normal-temperature pavement sections. Gradation and asphalt content analysis showed no significant aggregate segregation within the cooler areas. However, these cooler portions of the mat consistently showed higher air voids than the surrounding pavement. On the basis of numerous studies that have related AC deterioration and high air voids in a mix, it is known that the areas of a mat with higher air voids may experience premature failure compared with the time to failure of the mat as a whole.

Evaluating Project-Based Roadway Sustainability Rating System for Public Agency Use

To help the Washington State Department of Transportation (WSDOT) enhance its pavement preservation program through an improved understanding of the use of bituminous surface treatment (BST), the Highway Development and Management System was used as an analytical tool to test the average annual daily traffic and equivalent single-axle load levels appropriate as criteria for selecting the application of BST resurfacings to WSDOT pavements. It verified the feasibility of using BSTs to maintain pavements with higher traffic levels than have been applied in the past. Results also suggested that alternating the application of BST resurfacings and 45-mm hot-mix asphalt overlays is an effective rehabilitation strategy. Finally, the study results were used to estimate the impacts that increased use of BST surfaces would have on the performance of the state-owned route system.

The Highway Development and Management System in Washington State: Calibration and Application for the Department of Transportation Road Network

Greenroads, a system used to rate the sustainability of roadway projects, was used to evaluate 105 roadway and bridge projects in the United States for sustainable design and construction practices at various life cycle stages. A sustainability rating system can be a practical tool to help quantify and measure sustainability for a roadway project. The purpose of the investigation was to determine the state of the practice in sustainable roadway design and construction by application of Greenroads to a variety of actual projects. Forty projects identified as sustainable were compared with 65 typical projects representing conventional practice. The objectives of this study were to (a) identify trends in Greenroads project ratings, (b) benchmark the current state of the practice and identify potential areas for improved sustainability performance, (c) determine whether Greenroads can differentiate among projects on the basis of their sustainability efforts, and (d) identify the implications of these findings to practice. The results show that (a) some credits and categories are easily achieved, although achievement of others is more challenging and offers opportunities for improved environmental performance; (b) typical roadway projects tend to meet environmental regulatory standards but rarely do much more even when possible; therefore, they score fewer points for credits that focus on environmental benefits beyond the regulatory minimum; (c) contractors and materials suppliers appear to have unrealized opportunities to contribute; and (d) an early emphasis on the environment during project development appears to differentiate between typical and sustainable projects and manifest as higher Greenroads scores.

Quieter Hot-Mix Asphalt Pavements in Washington State

Several road-owning organizations are considering the use of project-based sustainability rating systems either now or in the near future. However, there is little information on how these systems might be evaluated or best used. Experience from the Oregon Department of Transportation (DOT) represents a reasonable approach to contextualizing and evaluating such rating systems. Early support by upper management and specific direction helped the Oregon DOT develop an organizational approach to sustainability within which a rating system could be evaluated for use. The Oregon DOTs interest in project-based rating systems led to its evaluation of the Greenroads rating system and use of it on three Oregon DOT in-progress projects. The Greenroads evaluation identified 11 sustainability best practices achieved by the Oregon DOT and identified 10 more that could be achieved for low additional effort, indicating potential for improvement. Ultimately, it appears that a sustainability rating system, when used in the proper context, can provide a flexible approach for an owner agency to measure, manage, improve, and communicate sustainability at the project level.