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Characterizing Bulk Porosity of CBPC Coatings on Aggressive Bridge Exposure


By Md Ahsan Sabbir, Florida International University

Presented at SSPC 2017; Session: Bridge Painting and Protection; Session chair: Mark Hudson

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Coatings are widely used to mitigate corrosion of structural steel in aggressive humid environments, but the service life is often diminished therefore novel coating systems have been proposed for steel bridge applications. Earlier research evaluated the performance of Chemically Bonded Phosphate Ceramic (CBPC) in aggressive lab and field environments. Preliminary findings indicated propensity for significant coating degradation after alternative wet and dry exposures as well as in alkaline solutions as observed by visual inspection, loss of coating thickness, and low pull-off strengths. Although earlier testing showed indication for possible steel substrate corrosion mitigation due to the development of an intermediate oxide layer, the initial coating degradation would likely reduce overall durability. The apparent porosity of the coating may facilitate enhanced moisture presence as well as enhanced ion and gas transport to the metal substrate to facilitate electrochemical corrosion processes. Mercury Intrusion Porosimetry (MIP) was conducted along with Electrochemical Impedance Spectroscopy (EIS) measurement. The MIP will give information about physical pore characteristics such as pore size, volume, distribution, connectivity etc. and EIS will provide information about electrochemical behavior related to pore characteristics. Assessment on the pore characteristics of degraded CBPC coatings in comparison to the as-received condition can be used to characterize coating quality, to validate coating and corrosion damage mechanisms and to provide coating parameters for serviceability projections.

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