Spot Painting to Extend Highway Bridge Coating Life: Volume 2: Research Overview (2018)

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NCHRP Project 14-30 51 CHAPTER 4 Overview of Project Tasks/Conclusions 4.1 Laboratory Testing One primary requirement of this project was to develop a test method to qualify coatings for use in spot painting repairs over typical existing coatings on bridges. This was addressed by using specially prepared test panels that replicated typical substrates encountered in spot painting (e.g. failed areas, boundaries and existing coatings). Common bridge coating types - acrylics, alkyds and epoxy with a polyurethane top coat were applied to the test panels to replicate “existing” bridge coatings. Both flat panels and complex shapes were developed for those tests using simple steel plates, and in the case of the complex shapes, the use of bolted plates. A key to the testing was the conditioning of exposed steel/mill scale surfaces by initially corroding them in a test chamber which both created rusted substrates and charged them with typical levels of chlorides found on bridges (excluding more severe exposures) to simulate the types of substrates encountered in the field. A surface preparation and painting protocol were developed to replicate the types of spot painting activities that could be adopted by most state highway agencies, eliminating the use of pressure washing operations which posed environmental obstacles to some state highway agencies for employing spot painting and required painting crews to spend extra time on site, waiting for washed surfaces to dry sufficiently for follow-up work. The panels were partially coated with six types of common liquid-applied coatings and two non-traditional coatings – a grease and a tape used as spot “repair” coatings. Brushing was used for the application as it is probably the one that would be most commonly used in the field for smaller projects. Several standard coating accelerated weathering and corrosion tests were used to test the coated panels - ASTM D5894 to replicate portions of bridges where coatings had bold exposures and ASTM B117 to replicate sheltered bridge locations with extended TOW. A nominal 5,000-hour test period was used as this was typically the standard test duration used by industry. The ASTM B117 tests proved more severe failing most of the liquid-applied coatings. One indicator of the success of the laboratory test protocol is the fact that it stressed the conventional liquid-applied coatings sufficiently to cause many of them to fail during the test procedures. This was due in part to the conditioning process that left soluble salts on substrates prior to painting and provided realistic conditions under which those coatings would have to perform. The use of SSPC-SP 3, “Power Tool Cleaning” represents a relatively low level of cleaning and restricts the use of coatings to barrier and inhibitive types that can provide good, but not optimal service compared to systems employing zinc primers. Of those systems, the best performing ones for the KTC test protocol were the barrier systems. Those KTC laboratory test results are supported by previous laboratory and field tests by KTC and others. The best overall performing liquid-applied coating system was the MIO – epoxy/polyurethane. It should be noted that the spot coatings that withstood the 5,000-hour test durations for both tests are probably well-matched to the durability of the existing coatings they were applied over. Unlike real bridges, the “existing” coatings used in the KTC tests were not weathered prior to the spot coating tests and had only experienced a short 250-hour exposure in a salt fog test used to corrode the unpainted areas of the test panels. After the 5,000-hour tests, a number of the “existing” coatings, where not covered by the experimental repair coatings, had begun to fail by either blistering or rusting while the areas where they were top coated by the “repair” coatings remained intact. The low water consumption salt remediation tests using chemical treatments showed that

NCHRP Project 14-30 52 it is possible to improve the performance of liquid-applied coatings with a minimal amount of effort and generation of wastewater. KTC researchers now wish they had that procedure on more spot coatings. Both soluble salt treatments showed some improvement in performance for several conventional coatings. Their benefit on the non-conventional coatings -the grease and tape - proved inconclusive as those coating passed the performance tests on both the chemically treated and untreated substrates. That approach might be beneficial in reducing or eliminating wastewater capture and disposal requirements that are problematic for some state highway agencies. A related task was to assess the potential service lives of those coatings. Service lives of spot coatings will depend upon the level of surface preparation including remediation of soluble salts. There is no widely accepted correlation between accelerated laboratory testing and subsequent service performance. However, KTC experience has generally indicated that test coatings remaining in good condition after 5,000 hours of either ASTM D 5894 or B117 will probably provide at least 10 years of service if applied over salt-free/low salt contamination substrates for atmospheric exposures in mild or moderate service environments. Most substrates found on bridges, even with soluble salt remediation, will have residual soluble salts, sometimes concentrated in pits that are difficult to eliminate. That can lead to lower service lives and, depending upon the type of bridge exposure, spot painting as set forth in the KTC method with conventional coatings will probably result in service lives of 5 to 10 years at some level of corrosion damage – probably in the range of 5%-10% for locations with significant initial rust and extended TOW. KTC has had limited experience with tapes, but the results are very promising. For spot repairs, they may be able to double or triple the service performance of conventional liquid-applied coatings with very little corrosion. Greases have provided good service for several highway agencies and are typically used to protect bridge bearings. If properly applied with sufficient film build and no missed spots, the grease tested should provide at least 5 years of service for atmospheric exposure in mild or moderate environments. Any suitably equipped coatings laboratory can conduct the tests as previously outlined. After performing the work, KTC researchers believe that the most cost-effective test of spot coatings is applying candidate coatings over flat panels that have been conditioned using either mill scale (for simplicity) or abrasive blasted steel that has been conditioned for 250 hours in a cyclic salt fog spray. Our preference would be for abrasive blasted steel for consistency in initial substrate condition. Use of flat test panels would significantly reduce testing costs compared to the additional testing of complex shapes (e.g. the Type II) panels. “Existing” coatings can be used, as in this test program, if a state highway agency wishes to evaluate a specific coating combination and a coating system comparable to those currently in service is available with the caveat that the test results may no reflect what will occur in the field. The grease and tape performed excellently in the laboratory and were the only coatings that survived for 5,000 hours of B117 testing on both the Type I and Type II specimens. This is reflected in actual highway service. Several highway agencies use greases to protect bearings and the Kentucky Transportation Cabinet has used them successfully since 2013. KTC researchers has four years of successful experience with the same generic type of tape in an aggressive environment under a leaking bridge joint on an interstate bridge. The pass/fail criteria used during the laboratory testing were based upon practical assumptions relating test panel performance to coating evaluations in the field. However, those are laboratory criteria. Use of the laboratory findings state highway agencies to adopt or reject coatings based upon the test results would be dependent on their evaluations of the test results. Some agencies might elect to perform testing for durations of 2 to 3,000 hours to reduce costs of laboratory testing.

NCHRP Project 14-30 53 There may be significant differences in coatings that can impact their performance. Coating approvals obtained under the laboratory test protocol should be for specific products, not generic classes of coatings. 4.2 KTC Field Testing KTC performed an extensive literature review to identify factors pertaining to the selection of spot painting as a maintenance painting option, along with proper handling of coatings, cleaning of repair areas, remediation of soluble salts, mechanical surface preparation, identification and verification of acceptable ambient conditions for painting, coating application, worker safety and environmental compliance – all within the scope of work performed using SSPC-SP 3, “Power Tool Cleaning.” As previously noted, KTC has prepared a guide for state highway agencies to use spot painting that addresses those factors and provides latitude for state highway agency determination of criteria for selecting, and methods for applying spot painting over a range of circumstances focusing on the SSPC-SP 3 method (though not exclusively). The elements of that guide can be used by agencies to develop procedures (work standards) for spot painting with in- house crews or to prepare specifications/special notes for spot paint work to be performed by contract. KTC researchers developed a field test protocol for using spot painting without washing. The KTC field work validated the guide’s criteria and methods to perform successful spot coating work on bridges with damaged coatings and corrosion. The field work also determined a limited correlation between the laboratory results and the field work. The field work was successfully completed using SSPC-SP 3 surface preparation with a variety of power tools and applying the 8 experimental “repair” coatings at three locations on the Bluegrass Parkway and KY 922 twin Bridges. Fortunately, the progress of the laboratory testing was slowed sufficiently to permit a 14- month performance evaluation of the field spot coatings. Presently, only a few correlations have been discerned between the laboratory test results and the field performance of the spot coatings. The acrylic (2 coat) system (Coating 7) performed poorly on bridge areas that previously were corroded and exposed to continuing moisture from leaking deck joints. The tape was performing well at several locations. The grease was failing slightly at one joint location though it performed well elsewhere. The other liquid-applied coatings were performing well where not exposed to leaking joints or applied over rough pitted surfaces. At locations under leaking joints, the liquid- applied coatings showed some degree of failure, but the service duration did not allow a long- range determination of which coatings would perform satisfactorily. KTC researchers recorded their experiences in performing the field work and provided ratings for the equipment and coatings that may prove useful to state highway agencies seeking to perform spot painting work with in- house crews. The NCHRP 14-30 spot painting guidance document and this report contain sufficient information for a state highway agency to: • Identify potential spot coatings and conduct field assessments • Select spot painting as a maintenance painting option • Identify issues that must be addressed to employ spot painting either by in-house crews or by contract • Prepare necessary standards or specifications to perform spot painting If a state highway agency wants to perform laboratory qualification testing to create or add coatings to a spot coating approved products list, it can adopt the KTC laboratory test protocol in

NCHRP Project 14-30 54 whole or part, as discussed above, to conduct accelerated tests to screen candidate coatings. The test protocol is fully described in Appendix B Spot painting is a valuable tool for state highway agencies to use in extending the service performance of existing bridge coatings. This report and the accompanying guide may prove useful in promoting wider use of the method and achieving its potential benefits. Moving forward, KTC researchers intend to disseminate these findings at conferences and meetings to promote the wider use of spot painting by highway agencies. 4.3 Conclusions The following conclusions are based on the KTC laboratory and field research: 1. The Type I test protocol developed under this project is suitable for identifying coating systems for spot painting repairs on bridges prepared using the SSPC-SP 3, “Power Tool Cleaning” standard. This includes substrates that are corroded due to moderate contamination by soluble salts and which are subject to a range of bridge micro- environments for mild and moderate atmospheric exposures. 2. The Type II-shaped test panels may prove useful if modified to prevent ponding of salt spray. Use of needle-gun power tool cleaning must be preceded by another cleaning process to remove excess contaminated rust which will prevent that material from embedding in the steel substrate. A modification to the test panel design is needed to eliminate the ponding issue. Due to project constraints, further work on this specimen type was not pursued beyond the initial laboratory testing and evaluation (i.e. no test protocol will be prepared for this type of specimen). 3. The best performing liquid-applied coating system for both test panel designs and test methods was a MIO-pigmented epoxy primer with a polyurethane top coat. Both non- traditional coatings — the grease and tape performed excellently for both types of test panels. 4. For the two test conditions obtained using ASTM D5894 and B117 testing, there were differences in test coating systems’ performance indicating that both test methods should be used unless actual field conditions strongly favor either direct UV exposure with condensation/evaporation for the ASTM D5894 tests or extended time of wetness with inconsequential UV exposure for the B117 tests. 5. The field spot painting tests incorporating the procedures in the accompanying guide were successfully used to apply the 6 liquid-applied coatings and two non-traditional coatings evaluated in the laboratory testing phase on three bridges. A 14-month follow- up evaluation of those applications revealed that they were generally performing as anticipated based upon the laboratory tests. 6. Both conventional liquid-applied and non-traditional coatings can function over SSPC- SP 3 prepared substrates with moderate soluble salt contamination in mild to moderate environments. Based upon KTC experience with similar laboratory testing and field evaluation of coating systems applied over SSPC-SP 3 substrates, it is likely that coatings passing or performing well in the KTC laboratory test protocol can last a minimum of 5 years with acceptable levels of deterioration and minimal corrosion of the coated steel substrates. Additional time is required to correlate the laboratory results with the remaining field samples on the two KY 922 Bridges which should remain in service for sufficient time to complete the laboratory/field correlations.