U.S. Department of Transportation
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Federal Highway Administration Research and Technology
Coordinating, Developing, and Delivering Highway Transportation Innovations
This magazine is an archived publication and may contain dated technical, contact, and link information.
|Publication Number: Date: March/April 2003|
Issue No: Vol. 66 No. 5
Date: March/April 2003
Research and Technology Services
Below are brief descriptions of reports recently published by the Federal Highway Administration's (FHWA) Office of Research, Development, and
Technology. All of the publications are available from the National Technical Information Service (NTIS). In some cases, limited copies are available from the Research and Technology (R&T) Report Center.
When ordering from NTIS, include the NTIS publication number and the publication title. You also may visit the NTIS Web site at www.ntis.gov to order publications online. Call NTIS for current prices. For customers outside the United States, Canada, and Mexico, the cost is usually double the listed price. Address requests to:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Toll-free number: 800-553-NTIS (6847)
Expanded Sales Desk Hours: 8 a.m. to 8 p.m. EST, Mon.-Fri.
Address requests for items available from the R&T Report Center to:
R&T Report Center, HRTS-03
Federal Highway Administration
9701 Philadelphia Court, Unit Q
Lanham, MD 20706
For more information on research and technology publications from FHWA, visit the Turner-Fairbank Highway Research Center's (TFHRC) Web site at www.fhwa.dot.gov/research/tfhrc/, FHWA's Web site at www.fhwa.dot.gov, the National Transportation Library's Web site at http://ntl.bts.gov, or the OneDOT information network at http://isweb.tasc.dot.gov/library/library.htm.
Study of LTPP Laboratory Resilient Modulus Test Data and Response Characteristics
The resilient modulus of every unbound structural layer of the Long-Term Pavement Performance (LTPP) Specific Pavement and General Pavement Studies Test Sections is being measured in the laboratory using LTPP test protocol P46. A total of 2,014 resilient modulus tests have passed all quality control checks and are included in the LTPP database with a Level E data status. As of October 2000, there were 1,639 resilient modulus tests yet to be performed. In some cases, these missing tests may have been performed but did not achieve a Level E status (did not pass all quality control checks) in the LTPP database. However, these test results have not been evaluated in detail. This report documents the first comprehensive review and evaluation of the resilient modulus test data measured on pavement materials and soils recovered from the LTPP test sections.
Pavement Smoothness Index Relationships
Nearly all State highway agencies use smoothness specifications to ensure that hot-mix asphalt (HMA) and portland cement concrete (PCC) pavements are built to high levels of smoothness. Not only is an initially smooth pavement generally indicative of quality workmanship, but also it has been shown to last longer than a pavement that is built with a rougher level.
About half of all current State smoothness specifications for HMA and more than three-fourths of all current PCC smoothness specifications are centered around the Profile Index (PI), as often measured using a profilograph. The vast majority of these specifications use a 5-millimeter (0.2-inch) blanking band in computing PI (i.e., PI5-mm). Unfortunately, because of the technical limitations of the profilograph equipment and PI computation procedures, the adequacy of PI5-mm in characterizing roughness and having it relate to user response has come into question.
The International Roughness Index (IRI) or the PI using a 0.0-mm blanking band (PI0.0) seem to provide better measures of smoothness and better correlation with user response. However, one barrier to more widespread implementation of these new smoothness standards is the lack of objective, verifiable correlation methods for use in establishing specification limits using the IRI or PI0.0. Assistance in selecting appropriate IRI and PI0.0 specification limits is needed to provide a basis for modifying current specifications to these more reproducible and portable smoothness indices. This research effort has developed a series of relationships between IRI and PI that can assist States in transitioning to an IRI or PI0.0 smoothness specification for HMA and PCC pavements.
Back-Calculation of Layer Parameters for LTPP Test Sections, Volume II: Layered Elastic Analysis for Flexible and Rigid Pavements
Publication No. FHWA-RD-01-113
This report documents the procedure and steps used to back-calculate the layered elastic properties (Young's modulus and the coefficient and exponent of the nonlinear constitutive equation) from deflection basin measurements for all of the LTPP test sections with a Level E data status. The back-calculation process was completed with the program MODCOMP4 for both flexible and rigid pavement test sections in the LTPP program. The report summarizes the reasons why MODCOMP4 was selected for the computations and analyses of the deflection data, provides a summary of the results using the linear elastic module (Young's modulus) for selected test sections, and identifies those factors that can have a significant effect on the results.
Results from this study do provide elastic layer properties that are consistent with previous experience and laboratory material studies related to the effect of temperature, stress-state, and season on material load-response behavior. In fact, more than 75 percent of the deflection basins analyzed with the linear elastic module of MODCOMP4 resulted in solutions with a root mean square (RMS) error of less than 2.5 percent. Those pavements exhibiting deflection-softening behavior with Type II deflection basins were the most difficult to analyze and generally were found to have RMS errors greater than 2 percent. In summary, the nonlinear module of MODCOMP did not improve the number of reasonable solutions significantly, and it is recommended that nonlinear constitutive equations not be used in a batch mode basis.