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Grout is often the last line of defense for corrosion protection of steel tendons in post-tensioned structures. The importance of bleed resistance in grouts used for post-tensioning has become more recognized. Ducts with vertical rise typically experience more bleed due to the increased pressure within the grout column. Intermediate bleed water lenses may form in tall vertical ducts, leaving a void through the cross-section of the duct exposing the tendon. Certain grout formulations are able to retain their water even under high pressures. These thixotropic grouts typically exhibit a "gel-like" state at rest, but regain their workability when agitated. The use of thixotropic grout can eliminate significant void formation when proper grouting procedures are followed. The present testing program correlates bleed under pressure tests such as the Gelman and API test methods to grout bleed resistance in ducts of various vertical rises. Preliminary property testing for workability and bleed resistance at different temperatures was used to achieve baseline bleed test data to correlate with performance testing. The performance testing involved pumping each grout into clear post-tensioning ducts of 2', 8', and 25' heights. |
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