The concrete pavement project, located on Interstate Highway 35 in Hillsboro, in the Waco District of the Texas Department of Transportation (TxDOT), involved the construction of a 9-inch post-tensioned concrete pavement (PTCP) and a 14-inch conventional continuously reinforced concrete pavement (CRCP) section. Construction on both sections started in June 2008 and completed in March. WW Weber is serving as the contractor for the project.
According to Moon Won, PhD, PE, associate professor in the department of cvil and environmental engineering at Texas Tech University and the research supervisor for the project, this project is a follow up to a test section completed in 1985 by TxDOT—a 1-mile 6-inch PTCP section on Interstate 35 in West, about 15 miles south of the location of the current project. The purpose of the 1985 project was to evaluate the viability of post-tensioned pavement construction and performance. According to Duane Schwarz, PE, director of construction in TxDOT's Waco District, after more than 20 years, that pilot project demonstrated the excellent performance of post-tensioning as very little (if any) maintenance has been required, despite being only 6 inches thick and experiencing very heavy traffic (around 30% truck traffic). To date, there have been no transverse cracks on the pavement. Based on these results, TxDOT initiated this new project.
"The performance of the 1985 post-tensioned pavement section has been excellent, and TxDOT wanted to find out whether PTCP could be cost-effective alternative to CRCP," says German Claros, PhD, PE, pavement research engineer at TxDOT. "We hope with this project to further evaluate the cost-effectiveness of PTCP in providing long-term pavement performance with minimum or no maintenance required."
To date, Won and his team have conducted deflection testing using a Falling Weight Deflectometer (FWD) on both the CRCP and PTCP sections. The deflections in PTCP are comparable to those at same thickness CRCP. Other measurements include strains and displacements of concrete slab and temperature and relative humidity of concrete. Further, the team plans to install gauges to measure prestress loss in the tendons.
"If it is determined that PTCP is a cost-effective pavement type, we will develop statewide design standards, material and construction specifications, and training materials to facilitate its implementation statewide," says Won.
According to B. Frank McCullough, PhD, professor emeritus of the department of civil engineering at the University of Texas, one of the most important aspects of this project is to evaluate the viability of post-tensioning in providing a comparable production rate to conventional concrete pavement. "The project in 1985 was only a mile in length and constructed using the fixed form method, which is not conducive for high production rates," says Schwarz. "The contractor for this modern project has figured out how to incorporate a slipform paver and is achieving paving speeds comparable to that of a slipform paver in conventional continuously reinforced concrete pavement."
Another key point, he adds, is that, on the existing project, the post-tensioned pavement is only 9 inches thick, resulting in a 5-inch savings in concrete materials. Additionally, because it is post-tensioned, cracking is virtually eliminated.
Won and his team currently are working with FHWA to host a workshop on the design, materials, and construction of PTCP in the first part of 2009.