The Texas Transportation Institute (TTI) is partnering with the Texas Department of Transportation (TxDOT) and several paving contractors around the state to field test a new quality control system for asphalt paving. Not only does the system designed by TTI give an accurate evaluation of the quality of the asphalt, it also relieves the contractor’s personnel from having to manually collect the information.
“Extensive research has shown that differences in temperature in the hot-mix asphalt relate to segregation,” says Stephen Sebesta, assistant research scientist with TTI. “Segregation is non-uniformity in hot-mix asphalt pavement materials. Our infrared system finds these differences in temperature and can pinpoint where pavement failure could occur.”
The system, called Pave-IR, uses thermal imaging to provide real-time measurements of material surface temperature. The Pave-IR test system continuously performs these profiles, providing more coverage and better documentation of thermal uniformity as compared to the existing test method.
“The new method is a major milestone,” says Sebesta. “We can now test 100 percent of the material in place, gathering continuous data for each day’s placement.”
The partnership between TxDOT, TTI and the contractor is actually formalized in TxDOT Standard Specification Item 341. The construction contractor is required to perform a thermal profile for each sublot in accordance with Test Method Tex-244-F. TTI then works with the contractor to provide the Pave-IR hardware, software and training to collect the thermal profile data.
“The system is easy to use,” says Arthur Gomez, manager of quality control with Silva Contractors. “TTI shows us how to install and run it one time, and then we pick it up. We run a segregation profile showing the variations in temperature so that we can modify the paver speed or rolling pattern if necessary.”
The system uses a thermal imaging bar with 10 infrared sensors attached to the back of the paver. The Pave-IR software package collects and displays the thermal profile in real time as the paving train progresses. Data collection does not slow production or placement of the mat, which is important to both contractors and TxDOT.
TTI has used the new system on about 15 construction projects throughout its development and implementation. Currently TTI is assisting with two TxDOT projects in the Odessa District and one in the Houston District.
Steve Smith, the director of construction with the TxDOT Odessa District, notes that the system allows them to sample all of the material as it is being laid down, not just a random sample as in current practice. This helps both TxDOT and contractors ensure a good quality pavement.
“If we get temperature differentials, then we can check air voids and density to determine if there’s a problem,” says Smith. “Contractors can address any problems in the pavement before it goes on too long and all the pavement needs to be replaced.” Obviously, replacing an entire section of pavement can be costly.
For the future, TxDOT plans to work with TTI to refine and improve Pave-IR, perhaps with ground-penetrating radar integrated for easier data coordination. “Some paver manufacturers have also expressed interest in the system,” says Magdy Mikhail, TxDOT pavement engineer and project manager. “If they acquire rights, they could make it part of the pavers they produce, saving contractors some costs.”
