Corrosion performance of coated steel bars in cracked and uncracked reinforced concrete beams
Textured epoxy-coated reinforcing bar (TEC) is a material which has gained interest from several Departments of Transportation (DOTs) for its ability to provide enhanced bonding to concrete thereby reducing cracking within transportation bridge deck systems. It aims to improve upon conventional smooth epoxy-coated reinforcing bar (ECR) by providing a multi-layered thicker and texturized coating. Where the texturized surface aims to improve the bond with the concrete, the thicker coating as compared to ECR aims to improve abrasion resistance, reducing the likelihood of impact-caused coating defects that could expose the underlying carbon steel that would lead to corrosion in road-salt chloride ion environments. Despite several studies investigating the mechanical performance of TEC as compared to ECR, no study has explored the long-term corrosion resistance performance of this new type of coating. This research aims to evaluate TEC’s long-term corrosion performance by subjecting reinforced concrete TEC specimens to service-level displacement loading and chloride ion exposure conditions that reflect realistic bridge deck conditions. As such, macrocell specimen subsets of uncoated, coated with holidays (intentional defects), ECR, and TEC reinforcing bar are curated and subjected to cycling chloride ponding. Additional ECR and TEC macrocell specimens are loaded in service-level displacement and then subjected to cyclic chloride ponding. Standardized corrosion benchmark tests such as half-cell potential (HCP) and macrocell current are employed to evaluate the performance of TEC relative to uncoated and coated reinforcing bar control samples. In addition, several experimental non-destructive testing (NDT) methods such as Ground Penetrating Radar (GPR), Ultrasonic Pulse Velocity (UPV), and Impact Echo (IE) are employed to assess the long term corrosion condition. Overall, it was observed that through 11 months of cyclic chloride ion exposure that the TEC bar specimens, both loaded and unloaded and with and without coating holidays, did not indicate any signs of corrosion per the standardized benchmark tests. Within all of the specimen subsets established within this study, only the uncoated bar specimens indicated corrosion per the benchmark tests, where values exceeding the corrosion thresholds for macrocell current and HCP were observed after 6 months of chloride ponding exposure. The TEC and ECR flexural specimens tested to service-level displacement controlled loading did not indicate any signs of corrosion activity, but the greater crack widths and load drop after first cracking observed in the ECR specimens as compared to TEC supports observations from literature that ECR has a comparatively weaker bond performance to TEC. Results from the NDT tests reveal that corrosion initiation in uncoated steel reinforcing bar may be detected in GPR signals through relative signal amplitude and the extent of internal concrete cracking caused by the service-level displacement loading procedure for the TEC and ECR specimens may be detected by UPV and IE test data, further showing that the cracking caused by loading in ECR resulted in more aggressive crack widths.
Textured Epoxy Coated Rebar, TEC, Epoxy coated rebar, corrosion, steel reinforcing bar, Non-Destructive Testing, NDT, Ground Penetrating Radar, GPR, ASTM G-109, macrocell corrosion, Half-Cell Potential, Impact Echo, Ultrasonic Pulse Velocity, corrosion detection, holidays, bridge deck corrosion
University of Illinois - Urbana-Champaign
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