In 2000, the Texas Department of Transportation (TxDOT) began constructing sections of eight heavily traveled roadways (mainly on I-35 between Laredo and Dallas) with thick, 15- to 20-inch asphalt layers. The hope was that the extra cost of so-called “perpetual pavements” would be recouped over their estimated 50-year lifespan since reconstruction would not be necessary. The only maintenance necessary would be the occasional need to provide a new riding surface.
With a Texas Transportation Institute (TTI) evaluation of all eight perpetual pavement projects in Texas well underway, Flexible Pavements Program Manager Tom Scullion announced his findings to the senior design engineers of TxDOT during a workshop February 1. Scullion’s research indicates that perpetual pavements in Texas are holding up well. The other good news: TxDOT can save even more money in construction costs by following his recommendations.
Scullion began his analysis in 2004, testing core samples and evaluating readings taken from non-destructive techniques using Ground Penetrating Radar and Falling Weight Deflectometers. The nondestructive testing and lab work determines the structural capacity of the current perpetual pavements.
“Our research indicates that the perpetual pavement concept is viable. We did find some permeability problems with one of the mix designs used, but a simple gradation change in the asphalt mixture should take care of those problems,” Scullion said. “Our findings also show that the pavement’s thickness can be significantly reduced, with no change in durability.” Scullion says his conclusions will hopefully be incorporated into the Texas standard design procedures.
As part of this effort, Scullion and fellow TTI Assistant Research Scientist Wenting Liu developed a software program (FPS 21) that will be used to determine optimal structural design for future perpetual pavements in Texas. Scullion and other employees of TTI’s Pavement and Materials Division will conduct classes by showing how TxDOT engineers can incorporate their findings into future structural designs.
Assistant Transportation Researcher Lubinda Walubita conducted the lab testing for the project and was essential in the development of the workshop.