Innovative Coating Removal Techniques for Coated Bridge Steel

About the report:

The purpose of this study was to determine if the use of a laser ablation coating removal (LACR) system would provide the Virginia Department of Transportation (VDOT) with an acceptable new alternative for removing existing coatings.  In this study, the LACR process was documented in the laboratory and in the field to determine the feasibility of implementing LACR for VDOT bridges.  All LACR work was performed on actual structural steel features from Virginia bridges.  Industrial hygiene surveys of the LACR process were used to determine the environmental and worker safety of LACR.  Laboratory material analysis of samples evaluated the effects on the properties of steel bridge components. 

This work led to the following conclusions. 

• LACR effectively removes the coatings investigated, including lead-based coatings.  Although microscopic investigation revealed that small coating particles remained on the surface after cleaning (which were not visible to the naked eye), this did not appear to affect subsequent coating adhesion adversely.

• The coating adhesion of LACR surfaces, tested by two independent laboratories, is acceptable.                             

• LACR does not detrimentally affect the mechanical properties of the ASTM A36 structural steel examined in this study. The tensile yield strength, ultimate tensile strength, ductility, and fatigue strength were on parity with expected values. 

• The industrial hygiene study results showed that the engineering controls associated with the LACR system maintained potential exposures to hazardous air pollutants for the laser operator well below the current Occupational Safety and Health Administration’s permissible exposure limit and action limit for each constituent sampled within a worker’s breathing zone and adjacent work area. This could provide a potential cost benefit, since LACR does not require the type of containment that traditional grit-blasting approaches require. 

• Similar to traditional coating removal technologies, the waste generated by LACR was classified as a regulatory hazardous waste; appropriate personal protective equipment must be worn during management of the waste material and filters.

• In the field, the LACR system was effective on bridge beam ends and bulk heads in open spaces but was more problematic in tight spaces where the geometry limited access to the coated surface.  The team did observe, but were unable to test in detail, other LACR systems that were smaller, lighter weight, and more powerful. 

LACR can be employed as a lead-based coating removal technique in preparation for other manufacturing processes, such as cutting or welding routinely performed by VDOT.  Such applications would not necessarily require high productivity rates or access to tight spaces.

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