Acceptance Tests for Surface Characteristics of Steel Strands in Prestressed Concrete (2008) / Chapter Skim
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Pages 9-19
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From page 9... ...
In the third and final phase, the promising surface and chemical test methods were performed on a different group of strand sources to validate their correlation with bond performance. At the direction of the supervisory panel, bond performance was quantified by another researcher using the pre-existing performance-based test procedure.
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From page 10... ...
Basis for Evaluation -- Transfer Length and Pull-Out Tests Transfer length is the most reliable and realistic measure of bond performance. During the screening testing, the evaluation of correlations between the pull-out tests and bond performance were based on performance as measured with transfer length tests conducted on the same sources of strand.
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From page 11... ...
Historic Strand KSU-F 1/2 Special 0.524 7 5/8 Left -- -- -- KSU Mar 2004 241 KSU-H 1/2 Special 0.523 7 1/2 Left -- -- -- KSU Mar 2004 209 SC-F 1/2 0.503 8 Left -- -- -- SC May 1997 223 SC-H 1/2 Special 0.530 7 1/4 Left -- -- -- SC Nov 2002 472 SC-IS 1/2 0.501 7 Left -- -- -- SC Mar 2003 682 101 6/10 0.601 8 1/2 Left -- -- -- SC Oct 2004 241 Recently Manufactured Strand 102 1/2 0.501 7 1/2 Left KSU Jun 2005 315 KSU Jun 2005 441 103 1/2 0.503 8 Left KSU Jun 2005 397 KSU Jun 2005 944 151 1/2 Special 0.517 7 1/2 Left KSU Jun 2005 273 KSU Jun 2005 541 153 6/10 0.588 9 Right -- -- -- KSU/SC Jun / Aug 2006 142/406 OSU Strand 349 1/2 0.505 8 3/4 Left OSU Jun 2004 156 -- -- -- 548 1/2 0.500 7 5/8 Left OSU Jan-Feb 2004 623 -- -- -- 697 1/2 0.503 7 1/4 Left OSU May 2004 606 -- -- -- 717 1/2 0.500 8 Left OSU Feb 2004 206 -- -- -- 478 *
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From page 12... ...
slip. The recently manufactured strand sources (102, 103, and 151)
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From page 13... ...
Since insufficient lengths of strand were available for pull-out and transfer length testing during the Screening Round from the historic sources, these tests were conducted only on the recently manufactured strand. The surface and chemical testing program has been conducted on both the historic strand samples and on the recently manufactured samples.
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From page 14... ...
2 dipChange in Corrosion Potential After ignition I Average change of potential Assess the potential for corrosion by comparing the corrosion potential to a reference cell monitored versus time Surface Roughness - I Roughness parameters Ra, Rz, Pc Quantify surface profile As received After Ca(OH) 2 dipCorrosion Rate After ignition II Corrosion current Determine the shift in potential of a metal sample from a stable corrosion potential due to an external current Warm water/acidchloroform wash Organic Residue Extraction Hot water/acidchloroform wash II Weight of extracted organic residue Determine amount of individual components of strand manufacturing lubricants from a warm/hot water wash procedure then an acid/solvent-wash procedure Sodium Calcium Potassium Boron Zinc Atomic Absorption (AA)
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From page 15... ...
from linear regression with average bond stress over transfer length.
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From page 16... ...
The first characterizes the early part of the bond stressslip relationship, while the second is based on the maximum stress measured throughout the test. In concrete pull-out tests performed on historic strand, the early performance was characterized in terms of the stress at which movement is first visually observed at the loaded end of the strand, called the stress at "first observed slip" or "first slip." For the tests conducted as part of this experimental program, the stress selected to characterize the early part of the bond stress-slip relationship is the bond stress at 0.1-in.
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From page 17... ...
For comparison with mortar pull-out test results for the Screening Round of testing, the loads at 0.1-in. slip provided from OSU were converted to average bond stresses at 0.1-in.
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From page 18... ...
The prediction interval concept is a necessary part of the development of acceptance/rejection thresholds for the recommended QC test methods, since, to conservatively ensure that a specified pull-out bond stress is achieved, the threshold on the QC test must be chosen as the value where the prediction interval lower bound is equal to the pull-out stress threshold. The regression model gives an estimate of the average pull-out stress if the pull-out test was actually conducted repeatedly on the same source of strand.
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From page 19... ...
The studies of surface roughness included metallographic studies of strand from poor and good bonding sources, scanning electron microscopical studies of the strand surface, and study of surface roughness by electrochemical impedance spectroscopy. Investigation of the concrete/strand interface included a study of the cement hydration at the strand interface, and a petrographic and chemical investigation of the strand/concrete interface in transfer length prisms in which poor bond was observed.
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