Anexo 1

Anlisis de caso

OUTDOOR PERFORMANCE OF ONE-COAT SYSTEMS

APPLICABLE TO NEW STEEL BRIDGES Yuan Yao*, Seung-Kyoung Lee**, Bob Kogler***

* Senior Chemist, SES Group & Associates, LLC, Fairfax, VA ** FHWA Coatings and Corrosion Laboratory Manager

Turner-Fairbank Highway Research Center, McLean, VA *** Principal, Rampart, LLC, Falls Church, VA

ABSTRACT

A two-year FHWA one-coat study was launched in November 2006 to evaluate various commercially available coating materials that can be applied as one-coat systems to new steel bridges. Seven one-coat systems, a 3-coat and a 2-coat control were selected and tested in three outdoor environments. After 24 months in marine environment and 18 months in natural weathering exposures in Virginia, the one-coat systems exhibited different degrees of deterioration. Except for urethane mastic, which developed eight medium size blisters and G5 grade rusting after exposed in the marine environment, most of the one-coat systems showed virtually no surface failures. The final mean rust creepage at the scribe ranged from around 2 mm for most of the one-coat systems to 30 mm for polysiloxane. When viewed collectively, none of the one-coat systems performed as well as the 3-coat control in the outdoor exposures.

INTRODUCTION A two-year FHWA in-house study was launched in November 2006 to evaluate various commercially available coating materials that can be applied as one-coat systems to new steel bridges. This study was initiated to respond to needs of the coating industry which desire to reduce the cost and improve the productivity in the steel fabrication shops. Performance of the coating systems was evaluated in the accelerated laboratory testing and outdoor exposure conditions. The accelerated laboratory testing has been completed in August 2008, and the test results were presented in the technical papers at PACE 2008 and 2009. 1, 2 A parallel outdoor study was completed in March 2009. This paper presents some of the preliminary outdoor test results.

EXPERIMENTAL PROCEDURE Coating Systems

While eight one-coat systems were selected in the accelerated laboratory study, seven one-coat systems were selected for the outdoor study. Glass reinforced polyester was not included in the outdoor study due to its delayed arrival for the panel preparation. Historically well performing one 3-coat system and one 2-coat system were also included in the both studies as controls. The selected coating systems are listed in Table 1. The chosen eight one-coat systems covered the most popular generic types of coating used for steel bridge protection. Test Panels and Surface Preparation All test panels were blast cleaned to the level of SSPC-SP 10. Measured anchor profiles of the cleaned steel panels were between 2.2 and 2.9 mils (55 m and 72 m). All coatings were sprayed on the cleaned test panels using airless spray method. A total of 222 panels were prepared for the entire study and they were divided into three groups. The type and number of panels for each group were listed in the previous PACE paper1. For the outdoor testing, 54 small panels (4 in x 6 in) in the second group were selected for a marine environment exposure testing in Sea Isle City, New Jersey. The third group consisted of 108 of 6 in x 12 in large size panels and they were tested in the outdoor exposure racks at the FHWA Turner-Fairbanks Highway Research Center (TFHRC), McLean, Virginia. Half of the test panels in each group were scribed diagonally following the instructions specified in American Society for Testing Materials (ASTM) Method D 1654.3 The scribes were made to evaluate corrosion resistance of a coating system at the artificial defect area. The other half of the panels were left unscribed to test coating properties such as gloss, color, pencil scratch hardness, coating impedance, etc. Exposure Conditions The test panels classified for a marine environment testing were exposed at an oceanfront test site in Sea Isle City, NJ. All the test panels were placed on a 45-degree angle wooden rack, facing directly south. The test site was considered a harsh environment with high chloride and high time-of-wetness.4 The test panels were sent back to the FHWA Coatings and Corrosion Laboratory every six months to evaluate on-going degradation. The total exposure duration was 24 months. The large size test panels were exposed at the TFHRC weathering test site. The test panels were placed on two wooden racks oriented at a 30-degree angle facing directly south. The panels placed on one rack underwent mild natural weathering exposure only. The panels placed on the other rack were sprayed once a day and 5 days per week with a 15 wt. % sodium chloride solution in addition to the natural weathering. Due to delay in experimental setup, the salt spray commenced three months late. The test panels were also evaluated every six months. At the completion of the outdoor testing program, all the panels were thoroughly examined for final performance evaluation. Coating Characterization and Performance Monitoring A series of characterization tests were conducted on the wet paints and coated test panels before the study started. Previous publications described more detailed information about the experimental procedures and methodologies.1, 2

As mentioned earlier, performance of the outdoor test panels was evaluated every six months. A low voltage holiday detector was used for detecting newly developed holidays.

The blistering and rusting were visually examined using the standard methods described in ASTM D 6105 and ASTM D 7146, respectively. The rust creepage developed at the scribe was measured according to ASTM D 7087.7 Electrochemical Impedance Spectroscopy (EIS) was used to monitor quantitative changes in coating properties. Digital photographs were taken to document the progressive changes observed on the panels. At the completion of the exposure testing, final evaluation was made in terms of extent of rust creepage, physical appearance, and number of surface defects. Changes in physical and optical properties such as gloss, color, pencil hardness, adhesion strength, and coating impedance were also evaluated.

REFERENCES

1. Seung-Kyoung Lee, Shuang-Ling Chong and Yuan Yao, The Most Recent Test Results of One-coat System Applicable to Steel Bridge Structures The Proceeding of the PACE 2009, New Orleans, Louisiana, February 15-18, 2009.

2. Seung-Kyoung Lee, Shuang-Ling Chong and Yuan Yao, Early Test Results of One- Coat Systems Applicable to Steel Bridge Structures, Proceedings of PACE 2008, Los Angeles, California, January 27-30, 2008.

3. ASTM D 1654 Standard Test Method for Evaluation of Painted or Coated Specimens Subjected to Corrosive Environments.

4. Peter Ault, Jim Ellor, John Repp, and Brad Shaw, Characterization of the Environment, FHWA-RD-00-030, August 2000.

5. ASTM D 714 Standard Test Method for Evaluating Degree of Blistering of Paints.

6. ASTM D 610, Standard Test Method for Evaluating Degree of Rusting on Painted Steel Surfaces.

7. ASTM D 7087-05a, Standard Test Method for an Imaging Technique to Measure Rust Creepage at Scribe on Coated Test Panels Subjected to Corrosive Environment.