Corrosion Initiation Projection for Reinforced Concrete Exposed to Chlorides--Part I: Black Bars

Corrosion of unbonded PT strands due to inadequate anchor pocket grouting was disclosed on 46 percent of approximately 4,800 tendons of a high rise residential and parking garage complex eight years after substantial completion.  No fractures had occurred; however, these are likely in the future as corrosion continues.  Consequently, 59 cables were extracted from various locations; and the remaining cross section area at the most corroded location was measured for those that exhibited attack.  Based upon 1) the mean and standard deviation for these areas, 2) the previously reported residual strength distribution for corroded PT wire,[1]^,[2] 3) assumed times at which corrosion first initiated and rates of subsequent initiation on other cables, and 4) assumed corrosion rates after initiation, a model was constructed that projects the time of future cable fractures.  Depending upon these assumptions, it was projected that the first strand fractures should occur in 2011-2012; and by 2019 from 929 to 1,733 failures are anticipated.
 References

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[1]   Hartt, W.H., Poeydomenge, A., Stauder, A-L., and Scannell, W.T., “Long-Term Effects of Cathodic Protection on Prestressed Concrete Bridge Components,” Report No. FHWA-RD-98-075, Federal Highway Administration, Washington, DC, April, 1998.

[2]     Stauder, A-L. and Hartt, W.H., “Cathodic Protection of Pre-Tensioned Concrete: Part I – Brittle Fracture Propensity of Corrosion Damaged Prestressing Tendon Wire,” paper no. 635 presented at CORROSION/98, NACE, March 22-27, 1998, San Diego.

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