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Ideally during bonded post-tensioned construction the grouting procedure occurs right after stressing of the strands. However, often times the tendons may not be grouted for weeks or even months after prestressing, due to harsh environments with extreme temperatures, long construction periods, or a case of staged construction. Consequently the need of protective agents against corrosion of the steel is required. Typically two temporary corrosion protection agents are used by the construction industry to safeguard the prestressing steel in the tendons. These are: Vapor Phase Corrosion Inhibitors (VPI's), and Emulsifiable Oils or Water Soluble Oils. The VPI's provide protection of a metal by a chemical reaction where a vapor is released and it stabilizes the deteriorating particles surrounding the metal preventing corrosion. The Emulsifiable oils are more commonly used in the field, and they are usually directly applied to the steel creating a protective film around it. With the use of these oils, friction losses during post-tensioning applications are reduced and corrosion protection may be achieved. This research program will focus on a series of tests to evaluate oiled strand in grouted post-tensioned tendons. Prior to grouting of the tendons is done, the oils might be flushed out from the ducts or left on the steel; in either case research has shown that residue oil left on the steel affects the bond between the grout and the prestressing strand. By lowering the bond between the steel and the grout, the overall system may no longer behave as a bonded system. The actual condition of the oiled strands with reduced bond lies somewhere between two cases: bonded (no oil) and unbonded. As a consequence the ultimate flexural field capacity of the oiled system may be lower than the ultimate designed capacity of the bonded system. The purpose of this study is to develop design criteria for oiled post-tensioned
systems and to determine the most promising emulsifiable oils. The program
has two phases; the first phase will include pull out tests and accelerated
corrosion tests (ACT) to select the best possible candidates for phase
II. Phase two will include large scale specimens tested to ultimate failure
and long term corrosion performance of the different oils. |
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