Publication Number: FHWA-HRT-06-028
Date: August 2006

Falling Weight Deflectometers: Transferring the Technology

For the Federal Highway Administration's (FHWA) Long Term Pavement Performance (LTPP) program, technology transfer is more than just sharing data and information. The LTPP program recently gave four of its falling weight deflectometers (FWDs) to FHWA's Western Federal Lands Highway Division (WFLHD), Central Federal Lands Highway Division (CFLHD), Turner-Fairbank Highway Research Center in McLean, Virginia, and the National Center for Asphalt Technology (NCAT) in Auburn, Alabama. These FWDs are now being used for pavement projects and research.

The FWD is a nondestructive testing device that can be used in structural testing for pavement rehabilitation, investigations, design, and research. The FWD imparts a dynamic load to the pavement surface that is similar to that of a single heavy moving wheel load. The resulting pavement deflection can then be measured. This deflection data combined with the pavement layer thickness can be used to determine the in-situ resilient modulus of layers within a pavement structure and analyze the remaining service life of a pavement.

"The FWD has been a very important piece of equipment to the LTPP program. It has allowed the structural monitoring of thousands of pavement test sections across North America since 1988 and contributed to the largest pavement deflection data set in the world," says Eric Weaver of FHWA. "As the LTPP program matures and test sections have been phased out of the program, there is less of a demand for the equipment. The LTPP program therefore felt that it would be mutually beneficial to transfer the technology to others that can use it."

Prior to the technology transfer, the CFLHD had contracted for FWD services on an as needed basis, primarily reserving FWD use for projects where many miles of testing were involved. However, now CFLHD will have the opportunity to use FWD testing for smaller scope activities as well, such as research, quality assurance, and forensic analysis. The FWD will get its first use in Mesa Verde National Park in Colorado, where CFLHD is planning to rehabilitate the main entrance road to the Park. A few areas of soft subgrade soil are known to exist along the project route. "The goal of the FWD testing will be to delineate the limits of this soft subgrade," says Mike Voth of CFLHD. "Overall project cost efficiency will be improved by developing a design solution for the soft subgrade areas separate from the remaining areas of the project, where better soil conditions exist." CFLHD then plans to use the FWD to evaluate pavement performance expectations on two recently completed projects in Utah's Zion National Park and Cedar Breaks National Monument.

NCAT will use the FWD at its test track, a 2.7-km (1.7-mi) full-scale flexible pavement test facility. "The FWD will be an integral part of the 2006-2009 research cycle, which will feature 46 test sections sponsored by various State departments of transportation and FHWA," says David Timm of NCAT. "It will aid in seasonal and temporal characterization of the test sections, measure structural integrity as a function of distress, and provide vital inputs for mechanistic-empirical pavement design validation and calibration." The FWD will also be used in conjunction with embedded pavement instruments to validate pavement response models.

The WFLHD has used its FWD for testing on the Going to the Sun Road in Glacier National Park in Montana to analyze the pavement's general condition and remaining service life and plan road repairs. It has also been used for testing on paved and gravel roads for the West Fork Road project in Montana. WFLHD had previously contracted for FWD testing to help with the design of pavement overlay thicknesses and to determine subgrade strengths and delineate soft subgrade areas. "By owning this equipment, the cost for this type of testing will decrease and allow for it to be used more often for not only design purposes, but also for construction needs," says Gary Evans of WFLHD. It will also aid in the future implementation of mechanistic-empirical pavement design methods. Other potential uses include forensic analysis of pavements, studies of remaining service life, pavement performance modeling for pavement management systems, and to analyze road thaw weakening effects to determine load restrictions.

For more information on using FWDs, contact Eric Weaver at FHWA, 202-493-3153 (email: eric.weaver@fhwa.dot.gov).

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