CoatingsPro Magazine

MAY 2017

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COATINGSPRO MAY 2017 57 Science Behind It By Ben DuBose N ow that you've read the CoatingsPro Magazine article about the Belle Vernon/Speers Bridge preservation project, explore the science and technology related to the control of bridge corro- sion, which is presented in these features from our sister publication, Materials Performance: 1. "Evaluating Sensors to Monitor Steel Corrosion in Concrete Structures" by Kathy Riggs Larsen, Materials Performance, February 29, 2016. http://www.materialsperformance.com/ articles/material-selection-design/2016/03/evaluating-sen- sors-to-monitor-steel-corrosion-in-concrete-structures. 2. "Failed Anchor Rods on the San Francisco-Oakland Bay Bridge: A Corrosion Discussion" by Norm Moriber and Kathy Riggs Larsen, Materials Performance, November 2, 2015. http://www.materialsperformance.com/articles/ material-selection-design/2015/11/failed-anchor-rods-on- the-san-francisco-oakland-bay-bridge-a-corrosion-discussion. 3. "Corrosion on the New Eastern Span of the San Francisco- Oakland Bay Bridge" by Yun Chung, MP 53, 11 (2014): p. 58. http://mp.epubxp.com/i/403882-nov-2014/60. "Mixed material will generate heat and should be handled appropriately, using all material before pot life expiration and cleaning lines and equipment immediately after use," states the Macropoxy 920 product data sheet. ough the 920 data sheet recommends a wet film thick- ness of 1.5–2 mils (38.1–50.8 microns), the Belle Vernon/Speers Bridge specifications called for a flood technique, in which the low viscosity primer is applied to the point that the excess runs off, according to Patoska. Finding the right application technique proved frustrating at first. "We tried rolling, brushing, two types of paint sprayers, and even big syringes," said Patoska. "Finally, one of our guys ran down to Home Depot and grabbed some hand pump spray bottles. at worked best." After observing the 920's minimum recoat window (approximately 12 hours at 77 °F, 25.0 °C, at 50 percent relative humidity), all core box corners, open crevices, open joints, and other areas with high potential for corrosion were caulked with Sherwin-Williams Loxon polyurethane sealant. e Titan crews built up the caulking-gun-applied, single-component sealant in a way to help shed water away from these problem areas. Edges and Welds and Rivets, Oh My! e two crews were now ready to apply the second coat. Macropoxy 646 is a two-component, high-solids, high-build epoxy designed to help ensure adequate coverage and protection for the bridge's many sharp edges, welds, and rivets. To achieve the specified 6‒8 mils (152.4‒203.2 microns) dry film thickness (DFT) in one pass, the crews again relied on their WIWA airless spray pumps, but they switched to 417 tips. To avoid creating holidays, bare areas, and pinholes, the crews used a 50 percent overlap with each pass and cross-sprayed at right angles where necessary. After honoring Macropoxy 646's minimum recoat window of approximately 8 hours at 77 °F (25.0 °C) at 50 percent relative humidity, the two crews were finally ready to apply the Belle Vernon/Speers Bridge's light blue topcoat. If luck held, the Belle Vernon-side and Speers-side crews would meet in the middle with enough time left over to spray the 450-foot-long (137.2 m) arch and meet the deadline. e topcoat specified was Sherwin-Williams Acrolon 218. e two-part, fast-drying acrylic polyurethane is formulated to provide color and gloss retention. Keeping with the #417 tips, the crews worked carefully to spray the 2- to 4-mil (50.8‒101.6 microns) topcoat in a single pass. Sure, the Titan crews worked diligently on every step of the way. But the Belle Vernon/Speers Bridge is a landmark structure seen by residents, visitors, railroad riders, riverboat passengers, and the occupants of more than 35,000 automobiles per day. Most people would notice The coating system included epox y primer and caulking on core box corners and a pass of Sher win-Williams Macropox y 646 at 6-8 mils (152.4-203.2 microns) dr y film thickness (DFT). This ma s sive projec t required much coordination on and of f site. Of fsite, the Titan crew needed adequate housing while working out of state. They rented 12 homes to accommodate the crew. Bridge Coatings

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