Linda M Pierce

Top-Down Cracking in Washington State Asphalt Concrete Wearing Courses

For years, pavement engineers within the Washington State Department of Transportation (WSDOT) have observed that longitudinal and fatigue (multiple-interconnected) cracks in their thicker asphalt concrete (AC) pavements appeared to crack from the top of the wearing course downward. Often, the cracks stop at the interface between the wearing course and the underlying bituminous layers (a depth of about 50 mm). Studies done elsewhere in the United States and internationally have reported similar results. The results of extensive coring that WSDOT routinely collects in its pavement rehabilitation process were compared in a study. WSDOT normally cores AC pavements to determine thickness for use in mechanistic-empirical design. In addition to coring for AC thickness, specific information noting surface-initiated (top-down) cracking with the crack depth or full-depth cracking was noted. WSDOT observed top-down cracking occurring in the thicker sections, with thinner sections cracking full depth. Top-down cracking generally started within 3 to 8 years of paving for pavement sections that were structurally adequate and were designed for adequate equivalent single-axle loads.

Calibration of Flexible Pavement in Mechanistic-Empirical Pavement Design Guide for Washington State

The Mechanistic–Empirical Pavement Design Guide (MEPDG) is proposed as an advanced pavement design tool that integrates up-to-date pavement practices. Since MEPDG was released in 2004, the Washington State Department of Transportation (WSDOT) has continuously worked on calibrating and evaluating the program with regard to implementation for state and local agencies. This paper presents WSDOTs latest efforts on calibrating the flexible pavement portion of MEPDG with data obtained from the Washington State Pavement Management System. It describes preparation of required input data and provides detailed descriptions of input values, as they may apply to states with similar conditions. The calibration process is described, and results and potential implications are discussed. Major observations and general issues encountered in the calibration process are emphasized. An implementation plan is being prepared that may replace the 1993 AASHTO Design Guide with MEPDG in Washington State. This study provides valuable conclusions for national applications: (a) the flexible pavement distress models were calibrated successfully, (b) WSDOT flexible pavements require local calibration different from the defaults, and (c) a software bug does not allow calibration of the roughness model. By making a few improvements and resolving software bugs, MEPDG software can be used as an advanced tool to design flexible pavements and predict future pavement performance.

CONSTRUCTION-RELATED ASPHALT CONCRETE PAVEMENT TEMPERATURE AND DENSITY DIFFERENTIALS

The Washington State Department of Transportation (Washington State DOT) examined temperature differentials in hot-mix asphalt paving over four construction seasons. From those studies it was found that low-density areas can be caused by temperature differentials in the mat. The study summarized is based on an examination of 17 projects during the 2000 Washington State DOT paving season to determine density differentials in the mat with a “density profile.” A density profile is a series of density readings taken in a longitudinal direction over a 15-m (50-ft) section through a low-temperature area. From this collection of density readings, the density range (the difference between the maximum and the minimum readings) and the density drop (the difference between the average and the minimum readings) are determined. The density range and drop are used to determine if low-temperature areas result in inadequate compaction. The criteria set forth by the Washington State DOT included temperature differentials greater than or equal to 14°C (25°F), a maximum density range of 96 kg/m3 (6.0 lb/ft3), and a maximum density drop of 48 kg/m3 (3.0 lb/ft3). Evaluation of the density profiles showed that when the temperature differential exceeded 14°C (25°F), 89% of the density profiles failed to meet the density criteria, but only 19% failed to meet the density criteria when the temperature differential was less than 14°C (25°F). It was found that pavements that experienced large temperature differentials during placement produced substantial density differentials.

Sensitivity of Axle Load Spectra in the Mechanistic-Empirical Pavement Design Guide for Washington State

The Guide for Mechanistic–Empirical Design of New and Rehabilitated Pavement Structures [referred to as the Mechanistic–Empirical Pavement Design Guide (MEPDG)] is proposed as an advanced pavement design tool that integrates up-to-date pavement practices. The use of axle load spectra instead of the equivalent single-axle load is a dramatic change. However, the collection of an adequate amount of data over years is required for the accurate characterization of future traffic for design; this gives primary importance to pavement designers having a good understanding of the axle load spectra. This paper presents the typical truck load spectra that satisfy the MEPDG requirements for the Washington State Department of Transportation (WSDOT) and that were developed on the basis of the data collected from selected WSDOT weigh-in-motion stations. Sensitivity analysis was conducted with various typical design parameters of WSDOT flexible pavements. The significant findings are that (a) one type of axle load spectrum can present load characteristics for WSDOT in MEPDG, (b) MEPDG is moderately sensitive to the axle load spectra for typical WSDOT pavement designs, and (c) WSDOT needs to calibrate MEPDG before use. The results have been verified in the calibration of the flexible pavement distress models for WSDOT. It is recommended that agencies that lack data resources test and use the default MEPDG axle load spectral inputs and that the bias may be corrected through model calibration efforts.

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

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

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

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...

Asphalt Concrete Overlay Design Case Studies

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.

Bituminous Surface Treatment Protocol for the Washington State Department of Transportation

During the late 1980s, the Washington State Department of Transportation (WSDOT), the University of Washington, and the Washington State Transportation Center developed a mechanistic-empirical flexible overlay design procedure. Following development, WSDOT implemented this overlay design procedure and has been evaluating flexible overlay projects for approximately the past 8 years. WSDOT rehabilitates about 100 projects each year; approximately 20 to 30 percent of the total projects are designed using the WSDOT overlay design procedure and the AASHTO overlay design procedure (using DARWin). These two procedures are discussed in general, and two case studies illustrate each of the overlay design procedures. Also included is the backcalculation of layer moduli from falling weight deflectometer data.

TEN-YEAR PERFORMANCE OF DOWEL BAR RETROFIT - APPLICATION, PERFORMANCE, AND LESSONS LEARNED

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

The Washington State Department of Transportation (WSDOT) has been rehabilitating its aged portland cement concrete pavements over the last 10 years by using dowel-bar retrofit, panel replacements, and diamond grinding. These pavements have been rehabilitated, with dowel-bar retrofit, to extend the performance life beyond the original design life of 20 years. The first dowel-bar retrofit application in Washington was constructed as a test section in 1992. Since then, WSDOT has dowel-bar retrofitted more than 350 lane-kilometers. Dowel-bar retrofit performance and application are described, and lessons learned in the last 10 years are discussed.