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39 CHAPTER 3 INTERPRETATION, APPRAISAL, APPLICATION The research study provided several important facts con- Application cerning surface preparation and application of TSMCs. Many of these confirmed existing guidelines, but others suggested The study found no differences among surface profile, future research that might lead to improvements in TSMC adhesion, and performance of coatings applied over steel performance. grades with differing hardness. Areas with extreme differ- ences in hardness, such as flame-cut edges, however, still require special attention in order to achieve satisfactory coat- INTERPRETATION AND APPRAISAL ing performance. The study also found no differences in the performance of TSMCs when they were applied to carbon Surface Preparation steel and HSLA steel. Even if surface preparation and coating application have The use of 100-percent grit provides better adhesion than been done properly, TSMC deterioration can occur at sharp does 100-percent shot. Using a 100-percent grit abrasive also edges and defects. The study confirmed that removing the provides better adhesion than either of the shot/grit mixtures sharpness of edges by slight curvature or grinding provides tested in this study. Shot/grit mixtures did provide better adhe- better coating coverage and adhesion. Although TSMCs are sion than 100-percent shot and might provide adequate corro- capable of protecting the substrate at narrow defects because sion performance. Shot/grit mixtures are sometimes used to of their ability to provide cathodic protection to the steel, improve equipment life because the shot is not as aggressive larger defects present a problem. Coating defects larger than toward the blasting equipment. However, these findings show relatively narrow scratches should be repaired. that, in order to improve coating adhesion, shot or shot/grit mixtures can be used for initial cleaning, and 100-percent grit should be used for final surface preparation. LONG-TERM IMPLEMENTATION PLAN The test results also show that not all 100-percent grit- The ultimate goal of this program is to have a guide to prepared surfaces are the same and that improvements in coat- TSMCs adopted by AASHTO. The keys to effective imple- ing adhesion can be achieved with improved angularity in the mentation are (1) identification of the user community, surface profile. This can be achieved through the use of fine (2) reports demonstrating and advocating the technical and angular grit. Measuring angularity can be performed in the cost benefits of this work, and (3) effective report and data field using a profilometer; however, interpretation of the data distribution. can be a problem. This study found correlation between pro- The probable user community for the project is large. At filometer measurements using a field-friendly instrument of a minimum, it extends to architects/engineers involved in RPC (peak count) and RQ (root mean square deviation) and bridge design, ferry terminal design, and DOT, FHWA, and adhesion; however, other research in the literature has not. transportation-authority engineers at headquarters, regional, Research is suggested to study the role of grit size and shape or divisional levels. The user community also includes indus- on surface profile and coating performance. Better definition try consultants and equipment manufacturers. of the values of RPC and RQ should be researched. Mean- The biggest impediment to implementation will be the while, an indirect method of ensuring an angular profile is higher cost of the TSMC materials in comparison with more suggested using grit classified as very angular, angular, and traditional coatings. People will, at first, only see the increased subangular with respect to an American Geological Society material and application cost. The user community has to grading system. understand that the cost benefits of TSMC materials outweigh Zinc TSMC should be considered for areas where salt con- the increased initial costs. They also need to understand that tamination is present because of its relative insensitivity to the cost of the coating materials and application are not as sig- salts. Where aluminum must be used, the surface preparation nificant as costs such as mobilization, containment, waste should include provisions for thorough washing of the sur- removal, and temporary removal of the structure from service face to remove chlorides. for any repair work. Studies have shown that TSMCs do not

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40 have to be replaced as often as liquid-applied coating. This can The test panels in continuous exposure at Corrpro's Sea make them more economical to use. This research includes Isle City, New Jersey, test facility, reported on in this study (discussed in Chapter 2). Research conducted by the U.S. Army Corps of Engi- neers; It is recommended that the guide to TSMCs and associated Research conducted by Rosbrook et al., Bhursari and articles on the benefits of TSMCs be presented in periodicals Mitchener, Bland, Kain and Young, Kuroda and Take- such as Roads and Bridges, Journal of Protective Coatings moto, Tsourous, Kogler et al., and the Platt Brothers and and Linings, Materials Performance, and at the TRB annual Company (11, 14, 4348); conference. It is further recommended that the Tri-Society The observations of the coatings at the North Carolina (AWS/NACE/SSPC) Thermal Spray Committee on Corro- DOT test facility at Ocracoke Island, North Carolina, sion Protection of Steel be addressed to assist in the dissem- reported in this study (discussed in Chapter 2); and ination of the guide.