Message Board Thread - "IR and asphalt roads"

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IR and asphalt roads WCT 3/28/2008
I've been looking for information on inspecting newly laid asphalt mats for segregation and have found little information about it past what is on the FLIR site. I've found other information about inspecting bridge decks with IR, but not new mats.

Any help would be appreciated.


Re:IR and asphalt roads Dusty 4/2/2008
WSDOT is an authority on HMA and IR. Look at , or .
Re:IR and asphalt roads WCT 4/3/2008
Thanks Dusty! I'll take a look at the links.
Re:IR and asphalt roads geologist 4/4/2008
The joint WSDOT/University of Washington research effort began using a FLIR ThermaCAM PM-280 infrared camera in 1998. The camera was used to image and measure to an accuracy of 1 degree F HMA temperatures in the trucks and as extruded by the paver with and without the use of material transfer vehicle or device.

The density of the imaged hot pavement areas was then evaluated by nuclear densitometry and the density results were correlated with the temperature measurements. It was found that in areas where thermal differentials in the hot mix after laydown were greater than 25 degrees F, air voids in the material increased by approximately 2% after curing, lowering the density and, therefore, the resistance of the affected areas to wear and tear.

Previous extensive field data showed that each 1% increase in air voids over a base threshold of 7% (based on a Rice Test maximum of 155) causes a 10% reduction in pavement life from physical and environmental wear and tear. On this basis, WSDOT correlated the thermographic data, nuclear density readings, and projected pavement life. The result — for the first time, a state DOT had a practical field test method and an economical tool, the infrared camera, to conduct quality assessments of HMA pavement mat during laydown that would accurately predict pavement life.

After an exhaustive series of tests of available road-building equipment, WSDOT concluded that a particular piece of equipment called the Shuttle Buggy, which is made by Roadtec, mitigated thermal segregation effectively, and far better than any other device tested. The Shuttle Buggy is called a material transfer vehicle, because it can accept HMA loads from trucks or pick up HMA from windrows, thoroughly remixes it with a powerful auger, and then transfers it into the paver machine. With the Shuttle Buggy in the paving train, hot mat temperatures consistently were well within the 25-degree window.

With the problem identified and a pragmatic and economical test method and solution in hand, WSDOT implemented a systematic density specification on 10 projects in 2002, and is applying the specification to all HMA road construction — a significant step for reducing premature road failure.

The specification has teeth and can be used to penalize contractors with price disincentives and other penalties when work does not meet state density standards. Kim Willoughby of WSDOT estimates conservatively that the use of thermography and reblending can save the state over $9 million annually in road repair costs by ensuring maximum highway lifetimes. Add the difficult-to-calculate hidden costs that are also avoided from delays to commuters and transporters, police details, damage to vehicles, and noise from construction vehicles. Now consider such savings on a nation-wide scale. The State of Washington has 3,384 national highway system miles — about 2% of the national total of 163,734 miles. So, projected savings could be $450 million a year.

The standardization of density profiling and the use of a thermographic protocol to identify density problems in road-building specifications offer important benefits for the paving industry and federal and state specifying agencies. These benefits include: longer lasting roads; improved return on road construction investment; maximization of the value of Superpave procedures; an extended paving season for contractors; and stimulus for the development of new protocols to maintain thermal consistency in batches of HMA during transport and laydown.


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