Corrosion-Induced Durability Issues and Maintenance Strategies for Post-Tensioned Concrete Bridges
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2022-09-01
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Edition:Final Report
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Abstract:Prestressed concrete structures utilize prestressing force, which can be applied using a pre-tensioning or posttensioning method. The Walnut Lane Bridge in Philadelphia, PA was the first precast post-tensioned (PT) bridge in the United States. It opened to traffic in the late 1950s and had to be replaced in 1990 after nearly 40 years of service due to improper tendon grouting and other deficiencies. Generally, for most of the second half of the 20th century, the durability of PT bridges in the United States was rated as good to excellent, even as PT bridges in Europe experienced tendon corrosion problems. Then, in 1999, the first failed tendon caused by corrosion in the United States was found in the Niles Channel Bridge in Florida. Since then, six other states—Virginia, Texas, Minnesota, Kansas, Indiana, and South Carolina—also experienced tendon corrosion problems in eight major PT bridges. Materials, specifications, construction methods, and inspection techniques for PT bridges have progressed greatly over the last two decades. Prepackaged non-bleed/thixotropic grout, flexible fillers, and corrosion-resistant strands exemplify improved materials. Additionally, tightened grout specifications and improved grout-injecting procedures can now minimize grout deficiencies. Another encouraging trend is the increasing use of advanced inspection tools such as high-powered borescopes, ground-penetrating radars, impact echoes, and magnetic-based nondestructive evaluation (NDE) systems. However, performing NDEs of prestressing steel in many critical structural locations prone to corrosion, such as the anchorage area, is still challenging. Additionally, once it is discovered, damaged prestressing steel often cannot be replaced. As PT bridges age, especially those constructed before 2001 with neat cement grout, more durability problems are likely to surface, with PT tendon corrosion likely to be a primary cause. This final report presents important findings from a 3-yr synthesis study on four aspects of corrosion-induced durability issues in grouted PT tendons, as follows: major cases of corrosion in the field, key findings of national and international laboratory studies, mechanisms of corrosion, and maintenance strategies for corrosion control.
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