Use of Steel Fibers for Induction Heating and Self-Healing in Asphalt Concrete

2016PDFTech ReportElseifi, MostafaPamulapati, YashwanthElbagalati, Omar SDhakal, NirmalLouisiana Transportation Research CenterLouisiana State University. Department of Civil and Environmental EngineeringLouisiana. Department of Transportation and DevelopmentUnited States. Department of Transportation. Federal Highway AdministrationLouisiana State University. Louisiana Transportation Research CenterUnited StatesAsphalt mixturesImage analysisInduction heatingMetal fibersMix designPavement crackingFHWA/LA.0x/xxx, LTRC Project Number: 16-5TIRE, State Project Number: DOTLT1000092Final Report, July 2015 \u2013 June 2016The objective of this study was to test the hypothesis that a new generation of asphaltic materials could be artificially healed while in-service by embedding metallic fibers in the mix and by applying an electromagnetic field at the surface. To achieve the objective of this study, an open-graded friction course (OGFC) was successfully designed and prepared to incorporate up to 5% steel and aluminum fibers by weight of the mix. The repeatability of the fracture resistance measurements was acceptable with a coefficient of variation ranging from 4.8 to 13.2% with an average of 8.0%. Based on the results of the experimental program, it was found that the control mix and the mix prepared with aluminum fibers exhibited greater ultimate load at failure prior to healing than the specimens with steel fibers. Yet, differences were not statistically significant. After numerous trials, the induction heating experiment was conducted successfully and showed the feasibility of inducing Eddy current in the metallic fibers without contact to the specimens. Eddy current flowed through the metallic fibers and caused heat due to the resistance opposing the current. Given their higher electrical resistivity, the specimens with aluminum required a longer heating time to reach 110\ub0C than the specimens with steel fibers. After the rest period, the control mix had the highest ultimate load after healing although it was not successfully heated through Eddy current; yet, differences were not statistically significant. This indicates that other healing mechanisms were present due to the recovery period, which allowed the control specimens to heal during the rest period. Healing efficiency was the highest for the control specimen as it approached 85%. Healing efficiency for the specimen with aluminum and steel fibers was 72 and 62%, respectively. Microscopic image analysis demonstrated that induced cracks healed efficiently during the healing period. Based on the results of the study, asphalt mixture healing through induction heating was validated and should be further evaluated by the Department through a comprehensive laboratory program. The evaluation of healing through induction heating in field applications should also be considered in future projects especially at the Louisiana Accelerated Loading Facility (ALF).131