Assessment of grouts for constructability and durability of post-tensioned bridges
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Post-tensioned (PT) bridge technology was first introduced in France in the 1930?s as described in the post-tensioned concrete bridges: Anglo-French liaison report by Highway Agency and is widely used in Europe and the US. PT bridge technology is advantageous over other bridge-type structures due to its larger span-to-depth ratio and reduced construction costs and time. This technology however faces several challenges due to potential corrosion of the prestressing steel. PT bridges constructed in the US during the 1970?s used cementitious grouts to fill the empty spaces in the PT ducts in order to protect the strands from corrosion. This grout in the ducts was intended to protect the strands from being attacked by aggressive agents and to prevent corrosion. A mixture of ASTM Type I cement and water was used as the grouting material for construction of PT bridges. In Texas, four major PT structures have been in place for more than 10 years. Recent investigations of the PT bridges in Texas did not identify any strand failures. However, the visual inspections identified voids in many of the ducts, especially at the ends of the bridge spans. These voids are believed to have been formed as a result of grout bleeding, poor grouting materials, and poor grouting techniques. One of the main performance requirements sought from PT grouts is their ability to fill existing voids in the existing ducts. Currently, many prepackaged grouts are available for PT application that are reported to not bleed and provide better flowability as compared to the older ASTM Type I cement grout. However, the current standard specifications for approving grout materials have limited requirements for evaluating the ?fillability? of these pre-packaged PT grouts. This research is being performed to provide modifications to the existing PT specifications such that PT repair grouts can be objectively assessed for fillability and long-term performance.