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NCHRP Project 14-30 72 APPENDIX A Instructions for Conducting Field Coating Condition Assessments
NCHRP Project 14-30 73 Field coating condition assessments can be performed in accordance with ASTM D5056, âStandard Guide for Assessing the Condition of Aged Coatings on Steel Surfaces.â A more comprehensive approach is provided in SSPC Paint Application Guide 5, âGuide to Maintenance Coating of Steel Structures in Atmospheric Service.â Those standards reference typical visual assessments of rust and coatings and procedures for evaluating them along with identifying/stipulating standard physical tests useful for evaluating condition of bridge coatings and the presence of contaminants that may affect existing and future bridge coatings. SSPC Guide 5 provides a complete overview of assessing, programming, performing, and following-up on bridge maintenance activities. A sample Florida DOT coatings rating sheet is provided in Appendix B and a Minnesota recommended list of equipment for performing field inspections is provided in Appendix C. Bridge plans can be used to: determine structure details and dimensions, identify the age of the structure, and calculate steel surface areas. In preparing notes/forms for a field assessment, the bridge can be subdivided into zones. Typical bridge zones can be: â¢ girder ends/bearings â¢ fascia girder exterior face â¢ interior girders/floor system â¢ truss/girder splash zone â¢ truss/girder/arch remaining members â¢ other areas A field survey should consist of the following activities: 1. Characterization of the service environment â The service categories of the bridge or specific zones can be assigned to aid in determining appropriate coatings for a project. The categories are provided in the SSPC commentary, âUsing SSPC Coating Material Standardsâ (Table 1). SSPC Environmental Zones (bridge service categories) are: 2A - Frequently wet by fresh water. Coating may be subject to condensation, splash, spray or frequent immersion. 2B â Frequently wet by salt water. Coating may be subject to condensation, splash, spray or frequent immersion. 2C â Fresh water immersion. Coating is constantly submerged. 2D â Salt water immersion. Coating is constantly submerged. 3A â Chemical atmospheric exposure, acidic (pH 2.0 to 5.0). 3B â Chemical atmospheric exposure, neutral (pH 5.0 to 10.0). 3C â Chemical atmospheric exposure, alkaline (pH 10.0 to 12.0). 3D â Chemical atmospheric exposure, presence of mild solvent fumes. Intermittent contact with aliphatic hydrocarbon solvents (e.g. mineral spirits), lower alcohols, glycols, etc. 2. Visual assessment of rusting â In evaluating the degree of rusting on painted bridge steel there are two industry standards, ASTM D610, âStandard Practice for Evaluating Degree of Rusting on Painted Steel Surfacesâ and, based upon that document, SSPC VIS 2, âStandard Method of Evaluating Degree of Rusting on Painted Steel Surfaces.â SSPC VIS 2 provides a visual method to evaluate the degree of rusting on painted steel surfaces using reference photographs that depict the percentage of rust with a 0-10 rating scale with â0â rating indicating greater than 50 percent rust and â10â rating indicating no rust. For intermediate rust grades, the rusting is categorized as spot, general, and pinpoint. Spot
NCHRP Project 14-30 74 rusting is when most of the rust is concentrated in a few areas. General rusting is when various sizes of rust spots are distributed across the paint surface. Pinpoint rusting occurs across the surface as dispersed small spots. A bridge component or zone may exhibit several degrees and types of rust. The general approach to rating the coating on a bridge is to: 1) divide the bridge into zones and evaluate each zone separately, determine the rust distribution (e.g., pinpoint), and assign the rust grade (from VIS 2 pictures). A 0.3 percent pinpoint rust would be rated at 7-P. The locations (zones), rust distribution, and rust grades (rust percentage) are pertinent information in rating coatings condition. Visible rust can be: â¢ Loss of coating with exposed steel â¢ Rust blisters â¢ Rust undercutting Visual inspection of the rust can indicate whether severe pitting or stratified/pack rust are present. These should be noted as well. 3. Visual assessment of coating deterioration â A bridge coatings condition visual assessment should note bridge zones having higher than normal levels of deterioration and unique environmental conditions (e.g., splash zones). This includes documenting the type of coating degradation present. Common types of coating degradation include: â¢ Loss of adhesion (peeling and curling) â¢ Cracking/checking/mudcracking â¢ Chalking â¢ Loss of gloss/fading â¢ Peeling and cracking can be rated together. The ratings can be: o None o Minor o Disbonded revealing bare steel Loss of adhesion can be assessed visually to identify whether a coating failure exposed metal/rust or resulted in inter-coat failure and which coating layer(s) has disbonded. Applicable standard methods include ASTM D660, âStandard Test Method for Evaluating Degree of Checking of Exterior Paints,â and ASTM D714, âStandard Test Method for Evaluating Degree of Blistering of Paints.â Chalking can be evaluated by ASTM D4214, âStandard Test Methods for Evaluating the Degree of Chalking of Exterior Paint Films.â Sometimes, chalking is difficult to detect visually (e.g., aluminum pigmented alkyd coatings in low-light environments). The presence of chalking can be determined by wiping the coating with a cloth (D4214 Method A). If an exterior topcoat is eroded by chalking sufficiently to expose underlying coats of paint, the condition can be evaluated using ASTM D662, âStandard Test Methods for Evaluating Degree of Erosion of Exterior Paints.â 4. Surface area estimates (repair areas for spot painting) â Steel coating area measurements can be made by take offs from plans. Coating failure locations can be sized and located in field notes. 5. Sampling to determine hazardous materials/existing coating type(s) â Field sampling of the existing coating can be performed using ASTM A 5702-2, âStandard Practice for Field Sampling of Coating Films for Analysis for Heavy Metals.â The sampling must be performed over a fixed area to determine the impact of future work that will remove or disturb the coating. Scrape samples are taken from the coating surface including all the coating system (i.e., primer, intermediate coat and topcoat). Several extractions should be performed to provide representative sampling of the bridge coating system. If several coatings types are used on a bridge, each one should be sampled. A minimum of several hundred grams of paint needs to be collected to identify any heavy (toxic) metals such as lead or PCBs that would impact worker safety and environmental protection requirements.
NCHRP Project 14-30 75 Those determinations can be made by follow-up laboratory testing. Coating samples can be tested for the presence of lead and other hazardous metals using Atomic Absorption Spectroscopy (AAS) or Inductively Coupled Plasma Atomic Absorption Spectrometry ((ICP-AES). These tests can be used to determine if the existing coating poses a potential hazard. Additional laboratory testing using Fourier Transform Infrared Spectroscopy (FTIR) can be used to identify the generic coating type(s) to determine any incompatibilities with subsequent maintenance coatings. 6. Evaluation of substrate defects (e.g., pitting, section loss, and rust scaling) â Pitting depths can be measured using pit gages. Section loss measurements may be necessary on critical structural elements (e.g. gusset plates, pin-and-hanger assemblies and other FCMs) especially where pitting is present. Thickness measurements can be performed per ASTM E797/E797M-15, âStandard Practice for Measuring Thickness by Manual Ultrasonic Pulse-Echo Contact Methodâ. Heavy rust scaling (stratified and pack rust) can be identified visually. Those locations should be documented. 7. Coating thickness and adhesion measurements â Coating dry film thicknesses (DFTs) can be measured using ASTM D7091, âStandard Practice for Nondestructive Measurement of Dry Film Thickness of Nonmagnetic Coatings Applied to Ferrous Metals and Nonmagnetic, Nonconductive Coatings Applied to Non-Ferrous Metalsâ. That specification includes the use of handheld magnetic pull-off (banana) gages and electronic gages. Those measure total film thickness of single and multi-coat coatings. When evaluating multi-coat coatings, a Tooke gage can be used to perform a destructive test per ASTM D4138, âStandard Practices for Measurement of Dry Film Thickness of Protective Coating Systems by Destructive, Cross-Section Means.â That test allows the inspector to determine the layers of existing paint and measure their thicknesses. It may be more reliable if the anchor profile under the existing coating can not be determined for nondestructive DFT measurements. The tape adhesion test ASTM D3359, âStandard Test Methods for Rating Adhesion by Tape Test,â (usually using an X-cut) is commonly used for field assessment of coating adhesion. Another field method is ASTM D6677, âStandard Test Method for Evaluating Adhesion by Knife.â That test also uses an X-cut and follow- up probing with a utility knife at the intersection of the two cuts to determine if the coating is adherent. An alternative or supplemental adhesion test can be performed per ASTM D4541, âStandard Test Method for Pull-Off Strength of Coatings Using Portable Adhesion Testersâ. The existing paint surface is lightly abraded with sandpaper and stubs/dollies of a known bonding area are glued to the paint. Those are pulled off with a portable hydraulic or pneumatic device with a load indicator. The maximum load divided by the bonding area provides the adhesive strength of the coating system (which may also be the cohesive strength of the weakest layer of coating if it fails internally). 8. Evaluation of substrate conditions âThe presence of previously blasted steel or mill scale substrates under coatings can be determined by destructive testing with a Tooke gage per ASTM D4138. Determination of an existing anchor profile on previously abrasively blasted steel requires thorough removal of an existing coating using a chemical paint stripper on test areas followed by profile measurement of the cleaned surface using a surface comparator, a portable stylus instrument or replica tape per ASTM D4417 âStandard Test Methods for Field Measurement of Surface Profile of Blast Cleaned Steelâ. Future maintenance painting over previously profiled surfaces can use DFT testing for measurements of repair coating thickness, but the gage needs to be calibrated for the existing substrate after surface preparation. 9. Soluble salt measurements â Soluble salts can be measured on bridges using methods in SSPC Technology Guide 15, âField Methods for Extraction and Analysis of Soluble Salts on Steel and Other Nonporous Substrates.â Field analysis of soluble salt surface contamination is commonly analyzed using deionized water and bonded latex
NCHRP Project 14-30 76 patches (in conjunction with conductivity meters) or by using a proprietary sleeve method with a slightly acidic test solution to extract surface chlorides and analyzed for chloride content using a miniature titration column (Guide 15 methods 4.2.2 and 5.25 respectively). The aforementioned firm also markets additional test kits to measure other surface salts including nitrates and sulfates. Testing can be performed on bridge steel in areas where corrosion is present or on painted surfaces in splash zones, such as exterior surfaces of fascia girders on overpass bridges. The test locations should be noted and soluble salt concentrations determined by conductivity (ÂµS/cm) or surface concentrations (Âµg/cm2). Note that conductivity readings can be related to surface concentrations by use of an appropriate conversion factor if the specific soluble salt ions are known. 10. Miscellaneous comments (e.g., extensive peeling paint, diesel fume contamination, build-up of bird droppings) â Bridge/coating conditions requiring special cleaning or surface preparation should be documented. 11. Evaluation of accessibility factors* â Access requirements for maintenance painting should be noted including bridge heights and clearances. Overpasses over railroads and clearance restrictions over roads and navigable streams should be noted along with potential access restrictions for maintenance painting. 12. Identification of sensitive environmental areas* â Adjacent areas containing potential environmental impacts (e.g. endangered species, raptors, drinking water inlets and parks) should be noted along with the potential environmental concerns and restrictions they might pose. 13. Traffic impacts* ââ The routes carried/spanned by a bridge should be noted as well as number of lanes/lane widths/travel directions/ADT to determine potential lane closures and access restrictions (e.g. off-peak hour access for painting) and traffic control requirements. 14. Determination of special bridge requirements* â Bridge locations in urban or scenic areas or prominent bridges (e.g. signature bridges) may require special aesthetic considerations. Conversely, bridges away the public view pose none. 15. Identification of potential work staging areas* â Identify potential staging locations that would accommodate vehicles, painting equipment, handling and mixing requirement (with access to painting operations) and storage locations for non-hazardous and hazardous wastes (if present). 16. Photographic documentation â Pictures should be taken of all painted steel (including areas with corrosion or deteriorated coatings), bridge locations requiring special cleaning, and areas on or around the bridge with environmental impacts and potential staging areas. * This information can also be gathered if site assessments are performed after a painting decision has been made.