Browsing by Subject "Grout"
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Item Development of Best Practices for Inspection of PT Bridges in Minnesota(Minnesota Department of Transportation, 2012-04) Berg, Kyle Matthew; Schokker, Andrea J.This report focuses on post-tensioned bridges built in Minnesota prior to 2003. The scope is limited to providing a targeted check of bridges that are most likely to have grouting related corrosion problems based on a review of plans and inspection notes. The project consisted of three phases: 1) review of plans and inspection reports of 40 post-tensioned bridges constructed prior to 2003, 2) selection of 10 bridges for a limited onsite inspection of the exterior of the bridge, and 3) invasive inspection of three select bridges. The bridges were selected to represent different bridge construction types to provide a spot check of the post-tensioned bridge inventory in Minnesota. One of the three bridges has corrosion and voids due to poor grouting, one has major corrosion problem related to construction issues (but appears to have good grout), and one showed no tendon corrosion or grouting problems during the invasive spot checks. Recommendations are given at the end of the report specific to the bridges that were investigated as well as for a general inspection plan for post-tensioned bridges in Minnesota. A concise guide for bridge inspection staff is provided that is specific to post-tensioned bridges.Item Durability of post-tensioning grout systems with mixed-In chlorides(2014-01) Thiesse, Benjamin LeeOne of the most important properties of concrete and grout is its ability to protect the structural steel that is essential to post-tensioned concrete. The purpose of this report is to determine the effect of various concentrations of chloride ions on the long term durability of pre-stressing strands embedded in grout. To achieve this objective, samples were created to mimic portions of a post-tensioned duct. Each duct was given a unique combination of chloride and water that would create an ideal environment for corrosion to take place. With the results of testing to date, it is clear that the amount of chloride is the only variable that was tested that had a significant effect on the rate of corrosion. The amount of water and characteristics of the specimen had a few trends but nothing that would lead to the conclusion that they play a significant role in the rate of corrosion.Item Quality Control Of Grouting For Post-Tensioned Tendons: In-Line Density Measurements(2019-03) Bray, JacobCementitious grout has proven to be an effective corrosion protection method in post-tensioning systems. While successful grouting has been used in numerous post-tensioned (PT) bridges, quality control of the material and placement in the field remains a challenge. During the grouting process on-site, ensuring that the grout being placed in the tendon is representative of the intended grout design is critical for the performance of the system. Inconsistencies in the placed grout can be attributed to varying mixing procedures used in the field (such as the addition of water above the design value). In some cases, grout passing the laboratory tests differs significantly from grout placed in the field. To alleviate these discrepancies, it is imperative that the PT industry improves quality control to ensure materials and products meet project requirements throughout production and placement - not just during the grout’s initial qualification. Advancements in the quality of in-place grouts can be made by refining specifications and developing a procedure to continuously measure the density of the grout as it is pumped into the tendon. The objective of this research is to develop a quality control measure that can be used during pumping to ensure suitable and consistent grout quality. Continuous monitoring and recording of the grout density will ensure the grout is of uniform quality throughout the project and meets the water content requirements provided by the grout manufacturer to meet project specifications. Recommendations for procedure and associated specification language is provided.