As asphalt is paved, aggregate can segregate, making weak spots in the pavement. Though hard to see, segregation can be detected by checking for differences in temperatures as the asphalt is laid.

Mounted on the paving machine, the new Pave-IR system uses infrared sensors to continuously monitor and record the location and temperature of asphalt as it is laid. Pave-IR helps contractors identify segregation as it happens, so they can correct it.

But its bigger benefit is giving them information that helps them improve the efficiency of their paving operations.

System detects and records thermal segregation The Pave-IR system, manufactured by MOBA Corp., Limburg, Germany, mounts on an asphalt paving machine and continuously records—in real time—the location and temperature of the asphalt as it is laid down on a road.

The system, which was available to Texas firms in the fall and debuted at the World of Asphalt 2010 Show & Conference in February, uses a display screen with colors that represent different temperatures. If the display shows a paving mat of uniform color, it means all the asphalt is about the same temperature and well mixed—and the pavement is good.

When areas of different color appear on the display, they indicate cool or hot spots. That’s important because big temperature differences may indicate that different-sized aggregates have segregated, creating a weak spot in the pavement.

The color-coded thermal profile makes it easy to see that paving is going well, or that corrections need to be made.

The thermometer that takes the asphalt’s temperature is a 13-ft-long bar that holds 12 infrared temperature sensors spaced 13 in. apart. Mounted across the rear of the paver, the bar monitors the temperature of asphalt as it is laid.

In addition to the sensor bar, the Pave-IR system includes a distance encoder mounted to one of the paver’s wheels, an optional GPS receiver and a computer that processes all the input to create a continuous record of the paver’s movement and the asphalt mat’s temperature.

The computer’s touch screen instantly displays the mat’s thermal profile and other collected information for the operator, foreman or quality-control technician to view while paving is in process.

The continuous stream of information enables the crew to fix problem spots and to adjust the paver for smooth, continuous operation that produces the best possible pavement.

Gene Smith, general manager of Smith & Co. of Conroe, Texas, says his firm purchased the Pave-IR to do “an even better job.

“It tells us what kind of mix we’re getting, how it’s going down and how uniform the mat is. The crew really likes it and so does the crew leader. It gives us vital information in real time so we can adjust to changing conditions right away.”

The paving record can be saved on a removable memory card for analysis by quality-control managers, or anyone who needs to review the operation’s results.

TxDOT incentives “Our overall goal in encouraging the use of Pave-IR is for contractors to have a self-improvement tool that helps them understand, control and improve their paving process,” says Dale Rand, director of the flexible pavements branch of TxDOT.

To that end, TxDOT is offering contractors incentives to use the Pave-IR system when they pave state highways with asphalt. Because the system can provide a continuous thermal profile of a paving job, contractors who use it don’t have to run density profiles.

As a second incentive, contractors who use Pave-IR on a job may still receive production and placement bonuses even if the pavement’s thermal profile shows some segregation.

TxDOT will also allow contractors using Pave-IR on a project to work when the ambient temperature drops as low as 32° F., as long as they can show there is no segregation. Normally, TxDOT will not let contractors pave when the ambient temperature drops below about 50° to 60°, Rand says.

“Being able to pave at lower temperatures could add a month or more to our paving season,” says David Morton, quality control manager for APAC-Texas Inc.’s Dallas office.