51314-4371-Corrosion propagation of dry-cast reinforced concrete pipes exposed to simulated field environments.

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Product Number: 51314-4371-SG

ISBN: 4371 2014 CP

Author: Francisco Presuel-Moreno

Publication Date: 2014

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Dry cast reinforced concrete pipes (D-RCP) are used in Florida at places in proximity to the shore or at locations where the water table seasonally saturate the D-RCPs. Previous studies suggest that corrosion would initiate after sometime in service once the critical chloride threshold has been exceeded at the reinforcement surface. However very little is known as to how corrosion would propagate for the environmental service conditions. Segments obtained from two different types of dry cast reinforced concrete pipes in which corrosion had initiated were used to investigate the corrosion propagation stage. The exposure environments investigated consisted of high humidity chamber (~95% relative humidity) partially or fully covered with saturated sand and fully or partial immersed in water. In some cases the exposure were sequential e.g. high humidity for 100 days followed by fully covered with saturated sand. In other cases the specimens were covered with saturated sand or immersed in water sometime after corrosion had initiated. During the propagation stage linear polarization solution resistance and corrosion potential were used as indicators of how corrosion evolved with time. On selected specimens cathodic polarization scans were periodically performed from open circuit potential (OCP) and polarized up to 0.25 V below OCP. The cathodic polarization scans were terminated earlier if these reached potential -0.85 Vsce as to minimize hydrogen evolution reaction at the reinforcement. These cathodic polarizations were done to assess when mass transfer limitations (oxygen) became significant. One argument that has been suggested is that if the concrete is water saturated then the corrosion rate of the reinforcement would be low. Only a modest increase in the linear polarization resistance values have been observed on specimens in which the potential of the reinforcement has transitioned (to values more negative than -0.65 Vsce). Longer exposure to the investigated environments might allowed to observe a reduction in the corrosion rate.