Effect of Voids in Grouted, Post-Tensioned Concrete Bridge Construction

Project Description

Post-tensioned (PT) bridges have several advantages: they can span long distances, can be constructed relatively fast, and are economical. The tendons of PT bridges are critical components, essentially the backbone of the PT bridge system. However, voids have been detected in the tendons of PT bridges in the United States and other countries with some of the strands in these voids exhibiting corrosion. A recent inspection of tendons in PT bridges in Texas identified voids. Researchers evaluated the corrosion performance of PT strands under various environmental and void conditions. Using these experimental data, the researchers developed time-variant probabilistic models to predict the tension capacity of PT strands subjected to different environmental and void conditions. Researchers found that the types of voids and resulting grout-void interfaces that are not parallel (or near parallel) to the strands result in localized corrosion at the interface and higher losses in strand capacity. However, environmental conditions lacking water and/or aggressive elements result in limited corrosion. If high humidity conditions are present and condensation occurs on the strands, corrosion activity can be high. Both uncontaminated and chloride-contaminated water can result in significant localized corrosion, reduced strand capacities, and early-age failures of the tendons. In addition to the electrochemical testing and structural reliability models, the researchers found that current methods for inspections and repairs were not well defined or efficient. Recommendations on inspections, repairs, and materials were developed. Efforts should be placed on identifying voids in tendons that contain or have contained moisture or aggressive elements. Moisture should be removed from these tendons and the point or points of infiltration should be repaired or sealed to prevent further infiltration. This includes repairing drain lines and ducts and protecting anchor heads, as these conditions can lead to early failure of PT bridges. Although repairing or filling the voids with grout has been temporarily suspended, researchers developed more efficient methodologies to fill the voids with grout. However, further research on the potential formation of galvanic coupling of strands embedded in both existing and new repair grouts needs to be assessed.

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