Mechanistic design research progresses to field

In 1999 the RPA commissioned a comprehensive two-year mechanistic design research project to be conducted by Consulpav International with cooperation from the University of Minho in Portugal as well as the Arizona and California Departments of Transportation.

The goal was to develop a mechanistic overlay design method based on reflective crack concepts. Since most current methods do not directly consider the phenomenon of reflective cracking in overlays, an integral part of the research centers on field measurements of crack activity.

Recent tests were conducted using the South Africa Crack Activity Meter (CAM). They took place during early January in Arizona and California when pavement cracks would be most open. It is the first time this type of research has been conducted in the U.S.

Several initial reports have been submitted to NCHRP 1-37A for consideration in the 2002 Pavement Design Guidelines. For highlights of the research contact the RPA office at 480-517-9944 or at www.rubberpavements.org.

Crack Research Team - Dr Jorge Sousa, left, and Dick Studstad, right, of Consulpav International, were joined by Carlos Palha, University of Minho in Portugal, to conduct a series of pavement tests using the Crack Activity Meter (CAM) developed in South Africa. The CAM, below, is placed over a pavement crack in preparation for testing.

CAM-FWD correlation - The testing compared the results from the CAM to that of the Falling Weight Deflectometer (FWD).Two sensors were removed from the FWD and placed on either side of the crack while the falling weight was dropped in a programmed cycle.

Data collection - Sousa operates a wheel traveling at the same speed as the truck, about 3 mph, past the crack. Movements of the truck are matched to the relative position of the CAM and the crack.