51314-4359-Corrosion Initiation and Propagation of Two Duplex Stainless Steels Embedded in Concrete

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Product Number: 51314-4359-SG

ISBN: 4359 2014 CP

Author: Francisco Presuel-Moreno

Publication Date: 2014

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Duplex stainless steels have been suggested as alternatives to carbon steel for structures that have a requirement of 100+ years of service life. Earlier investigations in the US used a duplex stainless steel where the mill-scale was not properly removed suggesting lower chloride thresholds than expected. Additionally most studies terminate the specimens upon corrosion initiations and/or add chloride ions to the concrete/motar/solution from the beginning. It is also not well known what the corrosion rate and corrosion extent during the propagation stage would be. In this investigation simulated deck slabs specimens with six rebars were prepared. The alloys investigated were UNS32304 and UNS32101. The concrete composition had a w/cm of 0.41 and 10% Fly Ash with not chlorides added at the time the concrete was prepared. All specimens contained a Titanium mix metal oxide (Ti MMO) mesh at the top face during casting (bottom face during exposure). The specimens were moist cured for 45 days and 15 days in the laboratory environment allowing the passive layer to form on the reinforcement surface. Wet (3 days) and dry (4 days) cycles were carried out for 120 days in an elevated temperature room (38 C). The solution used was 20% sodium chloride by wt. This exposure likely allowed chlorides to penetrate the concrete close to the surface. Phase two began and a migration cell approach was then periodically used to accelerate the chloride transport via two Ti MMO meshes. One mesh was placed in the solution reservoir and the second as mentioned above was embedded in the concrete. A potential difference of 20V was applied between the Ti MMO meshes. The electric field was applied for two to five days and then removed for periods of days to weeks. While the electric field is not in place linear polarization resistance and rebar potential vs. time were monitored. Several rebars appear to have become active at day 100 of Phase II. At least one specimen for each rebar type will be terminated to visually determine corrosion extent on each rebar. The chloride concentration at the rebar trace and as a function of depth will be determined.