LRFD Metal Loss and Service-Life Strength Reduction Factors for Metal-Reinforced Systems (2011) / Chapter Skim
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Appendix B - Test Protocols
Appendix B - Test Protocols
Pages 56-68
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From page 56... ...
Higher oxygen and salt content are anticipated near the surface, and higher moisture contents or free water near the base of a structure. Prior field programs have indicated that where groundwater intrudes at the base of the structure, higher corrosion rates should be anticipated.
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C-clamp connection sealed with epoxy Figure B-1. Typical installation of a corrosion monitoring station.
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and not all establish corrosion monitoring stations in the same manner including all the details as described in the section. In particular, Caltrans installs a cluster of 18 inspection rods in a grid pattern that includes six columns and three rows.
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describe the application of the LPR technique to MSE reinforcements. Polarization resistance measurements require an instrument to generate a plot of potential versus applied current (E versus iapp)
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Half-cell potential and LPR measurements are similar to those described for Type I reinforcements. Sonic Echo Measurements The sonic echo method (impact test)
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First, we may assess the difference in grouted lengths from these results to compare with the assumed lengths (corresponding to surface areas) used to interpret the LPR measurements.
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Corrosion Rates from LPR Measurements The corrosion current density is the current within the corrosion cell in the absence of any external sources. Stern and Geary (1957)
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From page 63... ...
relating polarization resistance to corrosion current density (icorr) , and the constants relating icorr to corrosion rate need to be known or assumed to compute corrosion rate from measurement of polarization resistance.
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Corrosion rates are computed using the polarization resistance with the correction for Rs. Once the uncompensated solution resistance is obtained, different operators will compute the same corrosion rate using Equations (B-1)
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. The observed loss of tensile strength is compared to the loss anticipated based on metal loss models proposed by Darbin et al.
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From page 66... ...
The ratio of maximum section loss to estimated uniform loss ranges from 1.2 to 4.8 with an average loss ratio of 2.4. The estimated uniform rate of metal loss is compared to the corrosion rate measured at an instant in time via the LPR technique.
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not galvanized 2B=bottom, M=middle, T=top 3NA = not available Table B-3. Summary of section loss observed from inspection rods exhumed by Caltrans.
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From page 68... ...
This is more of an issue at sites with relatively poor or marginal quality fill materials where metal loss is less uniform and localized loss of zinc is observed. In general, corrosion rates from LPR measurements are consistent with observations of maximum metal loss considering a factor between 2 and 3 relating the average to the maximum metal loss.
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