Evaluation of Combining Heat Induction and Laser Ablation for the Removal of Potentially Hazardous Bridge Coatings

About the report:

This project aimed to evaluate whether combining induction coating removal (ICR) and laser ablation coating removal (LACR) could be combined to remove hazardous bridge coatings at practical rates. This study included evaluations of the coating removal rates, surface cleanliness, surface profile, steel substrate mechanical properties, recoating adhesion performance, field demonstrations, and environmental and industrial hygiene evaluations of ICR, LACR, and ICR first plus LACR afterward (ICR+LACR). Coating removal data showed that using ICR+LACR could result in a coating removal rate approximately 10 times faster than using LACR alone. ICR can quickly remove the bulk coating layers but leave the residual primer on the steel surface. LACR can then quickly remove the remaining primer layer to provide a clean surface ready to be recoated.

Surface analysis showed that LACR provides a much cleaner surface, with fewer contaminants embedded in the surface compared with grit blasting. LACR also leaves less of a surface profile compared with grit blasting. However, LACR surfaces still meet the Virginia Department of Transportation (VDOT) specifications for surface profile before coating.  Metallography and mechanical testing showed that the heat from LACR, ICR, and ICR+LACR changed only a very thin layer of the steel substrate, but this change did not affect the mechanical or fatigue properties of the underlying steel. Adhesion testing of inorganic and organic zinc coatings applied to LACR and ICR+LACR surfaces showed acceptable levels of adhesion that were comparable with surfaces cleaned by grit blasting, and the adhesion values met the coating manufacturer’s recommendations. These findings are notable because, although LACR surfaces have a smaller profile than grit-blasted surfaces, LACR surfaces are much cleaner, thereby creating sufficient adhesion.

Environmental and industrial hygiene measurements indicated that LACR units that do not use an effective built-in fume extractor can expose employees to unacceptable levels of laser-generated air contaminants during coating systems removal. The quantity of hazardous waste generated by LACR and ICR is less than the amount of waste created through traditional blasting measures. ICR waste is not captured through debris collection and should be contained on tarpaulins or other similar drop cloths.

This study recommends that VDOT develop guidance and specifications for using the ICR+LACR method for bridge coating removal. The study also recommends that VDOT identify upcoming bridge coating removal projects, such as girder end recoating and repair projects, for which ICR+LACR could be specified or permitted as a removal method. In addition, the Virginia Transportation Research Council should initiate a technical assistance project to evaluate the mechanical properties of high-strength bolts subject to heat, such as from ICR. VDOT can achieve an environmentally and worker-friendly coating removal method by using ICR+LACR. This method is a competitive alternative to grit blasting and can be used in targeted locations to help extend the service life of steel bridges.

Supplemental materials can be found at https://library.vdot.virginia.gov/vtrc/supplements.

_{Disclaimer Statement:The contents of this report reflect the views of the author(s), who is responsible for the facts and the accuracy of the data presented herein. The contents do not necessarily reflect the official views or policies of the Virginia Department of Transportation, the Commonwealth Transportation Board, or the Federal Highway Administration. This report does not constitute a standard, specification, or regulation. Any inclusion of manufacturer names, trade names, or trademarks is for identification purposes only and is not to be considered an endorsement.}

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