FHWA Grant Program Helps Industry Improve Asphalt Testing

A Technology Partnerships grant program from the Federal Highway Administration (FHWA) helped an Ohio company develop a prototype into a testing tool that will help the asphalt industry predict pavement failure and cut roadway costs.

The grant program — a part of the FHWA Highways for LIFE initiative to accelerate innovation — provides funds to private industry to turn promising innovations into market-ready products that can enhance highway safety and quality and reduce the impact of construction congestion on travelers.

EZ Asphalt Technology, LLC of Athens, OH, used $225,061 of FHWA Highways for LIFE grant funds to develop the Asphalt Binder Cracking Device (ABCD). Low-temperature cracking is a major cause of asphalt pavement failure. Resistance to thermal cracking is provided primarily by the asphalt binder that bonds with aggregates to create hot-mix asphalt. The ABCD uses a simple, reliable method to pinpoint the temperature at which asphalt binders will crack, so it can help engineers select proper asphalt binders for paving projects based on climate.

“Thermal cracking is a significant and costly problem,” said Dr. Sang-Soo Kim, owner of EZ Asphalt Technology and associate professor of engineering at Ohio University, who developed the ABCD concept.

“Highways for LIFE helped transform the ABCD from a research tool to a problem-solving tool that can be used in real life,” said Kim.

Creating field-like conditions

Unlike conventional test methods for estimating the low-temperature cracking potential of asphalt binders, the ABCD creates thermal cracking conditions similar to those in the field.

The unit consists of a metal ring equipped with temperature and strain sensors that fits into a silicone mold. After heated asphalt binder is poured around the ring, it is placed in an environmental chamber that cools the sample at a predetermined rate.

As the temperature drops, the asphalt binder contracts more than the metal ring, causing the binder to fracture. A computerized data acquisition system, which records strain and temperature readings at 10-second intervals, captures the temperature and stress level at which the fracture occurs. That information can be used to grade asphalt binders for expected climate conditions, as well as to develop new binders that can better withstand frigid temperatures.

A set of four specimens takes about two hours to prepare and about three hours to cool in the testing chamber to determine the cracking temperature. The cracking temperature is determined directly from the real-time graph of binder temperature and strain versus time. The testing chamber can hold 16 specimens at once, allowing different binder samples to be tested simultaneously.

Improved test method

The ABCD is an improvement over conventional test methods, which have a greater margin for error because of the absence of critical information such as the coefficient of thermal expansion and tensile strength, said Kim. In particular, he said, tests have shown that the ABCD produces more accurate test results for binders that contain polymers, which are becoming more common in the United States.

The American Association of State Highway and Transportation Officials (AASHTO) has made the ABCD test procedure a provisional standard, TP92 — Determining the Cracking Temperatures of Asphalt Binder Using the Asphalt Binder Cracking Device, the first step toward final adoption as a standard. AASHTO adopts provisional standards on a temporary basis so the highway community can have access to new technologies and procedures quickly, and it can convert a provisional standard to a full standard any time during the eight-year temporary period.

Technology Partnerships tests

Under the Technology Partnerships program, the ABCD went through a two-phase testing process. The first phase involved improving the ABCD test procedure and refining the equipment and analysis software. Ruggedness tests were conducted at the North Central Superpave Center in West Lafayette, Indiana, the University of Wisconsin–Madison, and EZ Asphalt Technology to determine the effects of a variety of factors on the ABCD test method.

In the second phase, 31 laboratories participated in a study to evaluate the repeatability, accuracy, and simplicity of the testing system. The volunteers included 18 State and Federal government labs, one Superpave Center, one Canadian Ministry of Transportation lab, five universities, and six private facilities.

Technicians at each lab set up the ABCD testing system and conducted a series of three test runs on three sets of asphalt binder specimens. Despite limited experience using the device, almost all participating labs were able to complete the tests without major difficulty. Results of the tests showed that the standard deviation of the temperature was within an acceptable range of precision.

Ten labs also conducted a Bending Beam Rheometer (BBR) test, the current Superpave test for low-temperature grading, on the asphalt binder samples. The results indicated that the precision estimates of ABCD cracking temperature and BBR critical temperature were comparable.

Users provided feedback on their ABCD testing experience, which was used to further refine the test procedure. Several reported that trimming the poured asphalt sample was difficult, so the test procedure was simplified to eliminate that step without affecting the test’s accuracy. User comments from the survey included the following:

  • “ABCD unit was very user friendly, software was excellent, and I personally would recommend this to anyone into binder testing.”
  • “Easy to use. The instructions were well written and easy to follow. The setup did not take long and the macro ran great to get the cracking results.”
  • “Easy-to-understand concept. Simple results.”
  • “I was impressed on how easy the ABCD was to use. Once you get the sample prep technique down, the rest of the procedure was simple to use.”
  • “Easy test to perform with a very simple test procedure. Relatively easy to clean up. I think this is great test with the potential to replace the BBR [Bending Beam Rheometer] and DT [Direct Tension] tests in the future.”

“Most labs reported that the ABCD was an easy test to run,” said Kim. “Engineers and technicians liked the fact that they could see the performance of the tested binder directly without additional analysis.”

Now that the Technology Partnerships project is completed, EZ Asphalt plans to develop a range of ABCD models to satisfy industry’s different needs. “We plan to address the feedback of the participating labs, and we already have significantly refined the test equipment and procedures,” Kim said.

To learn more

For more information on Technology Partnerships, visit www.fhwa.dot.gov/hfl/tech.cfm or contact Julie Zirlin at julie.zirlin@dot.gov or (202) 366-9105. For details on ABCD, go to www.ezasphalttechnology.com or contact Sang-Soo Kim at (740) 597-3230 or skim@ezasphalttechnology.com.