Durability and Behavior of Prestressed Concrete Beams. Report 5. Laboratory Tests of Weathered Pretensioned Beams.

摘要

This report is the fifth in a series describing a study which is being conducted to develop information on the durability of prestressed (pretensioned and posttensioned) concrete beams. This report describes tests and observations on two beams that had been exposed to severe weathering for 16 years in a flexurally loaded condition at the Treat Island, Maine, exposure station. The laboratory tests conducted on these beams consisted of examination and tensile testing of the steel prestressing (pretensioning) strands after removal from the beams and also tests to determine depths of carbonation and chloride penetration into the test beams. Conclusions: (1) The steel prestressing strands were heavily corroded due to spalling of the concrete and detachment of the protective epoxy end pads. The corrosion was heaviest at the ends of the strands, but it was also heavy in some areas of the midportion of the strand. (2) The corrosion of the strands was so severe that the eight strands tested in tension (four from each beam), none of the strands passed all of the ASTM tests for tensile strength or elongation under load. (3) The corrosion on the center wire of each strand was of the same intensity as that on the outer wires. (4) In areas of heavy corrosion of the strand, there was no cement paste stuck to the strands. (5) Results of tests to ascertain depth of carbonation indicated that carbonation was not a factor in the corrosion of the steel. (6) Results of tests to ascertain the degree of chloride contamination revealed that there were sufficient chlorides present to be a major cause of corrosion of the prestressing strands.