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An Incentive To Take Asphalt’s Temperature

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A new thermal-imaging device is helping contractors build better roads, and transportation owners are offering incentives to use it.

Photo: APAC-Texas
Pave-IR measures the temperature of fresh asphalt in real time.
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Available since last fall and officially rolled out at the World of Asphalt in Cincinnati in February, the new system, called Pave-IR, continuously monitors and records the location and temperature of asphalt as it is laid. Pave-IR helps contractors identify segregation, or weak spots, in the pavement as it happens.

Manufactured by MOBA Corp., Limburg, Germany, the unit uses sensors and 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—the pavement is in good shape. When differently colored areas appear on the display, they indicate “hot” and “cool” spots, indicating the mat’s trouble spots.

The “thermometer” 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 the asphalt mat as it is laid. In addition to the sensor bar, the Pave-IR system includes an odometer mounted to one of the paver’s wheels, an optional GPS receiver and a computer that processes all the input, creating a continuous record of the paver’s movement and the mat’s temperature.

The computer’s touch screen displays the mat’s thermal profile and other information for the operator, foreman or quality-control technician. The continuous stream of information enables the crew to fix problem spots and adjust the paver on the fly.

Highway owners, such as Texas Dept. of Transportation, are offering new incentives to use this technology. “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 TxDOT’s flexible pavements branch.

To that end, TxDOT is offering contractors performance 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.

Also, TxDOT will allow contractors using Pave-IR on a project to work when the ambient temperature drops to 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 to below about 50˚F to 60˚F, 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 roadbuilder APAC-Texas Inc.’s Dallas office. Gene Smith, general manager of Smith & Co. of Conroe, Texas, adds that his roadbuilding firm purchased a Pave-IR to do “an even better job.” The unit, he explains, “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 else who needs to review the operation’s results.

The idea for Pave-IR started in the late 1990s, when TxDOT was looking for a more scientific way to identify segregation in asphalt paving. It presented the challenge to the Texas Transportation Institute at Texas A&M University.

“The traditional way of identifying segregation in asphalt was looking at the pavement’s surface texture,” says TTI associate transportation researcher Stephen Sebesta. “It was subjective.” After a researcher in Washington state showed that thermal imaging could show segregation, TTI began developing a system.

Originally, TTI’s early work planted Sebesta and an infrared camera in the bed of a pickup truck that would drive beside the paving train. Sebesta took heat-sensing photos of the newly laid asphalt, each photo covering about 20 ft, then manually recorded the time and location of each shot. To get a continuous view, he had to stitch the individual photos together electronically on a computer.

After a few years of experimentation, as well as a growing availability of smaller, cheaper infrared sensors, TTI developed a system for monitoring asphalt paving that could cover an entire lane and record paving performance continuously all day long.

TTI’s research, development and testing yielded the system that has become Pave-IR, but TxDOT and TTI needed a manufacturer that could produce, sell and support it as a commercial product. That’s when paver-control expert MOBA Corp. joined the team. The team also developed the system’s Pave Project Manager software, which helps build custom reports, displays temperature graphs and analyzes project results.

The system lists for $23,500, plus installation and a week of training, according to Joey Farrell of Jobsite Technologies LLC, a dealer in Atlanta. However, as useful as Pave-IR is for documenting paving quality, many contractors say the system’s ability to help them analyze their perations and improve efficiency is even more valuable.

“Pave-IR information tells you how well your plant operator, trucking provider, paver operator and ground man are working together,” says Farrell. Adds APAC’s Morton, “The industry has needed this for a long time.”

[A version of this story originally appeared in Texas Construction.]

 

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