51315-5837-Corrosion Propagation Under Modest Accelerated State

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Product Number: 51315-5837-SG

ISBN: 5837 2015 CP

Author: Francisco Presuel-Moreno

Publication Date: 2015

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The corrosion propagation period is typically assumed to last about five years for carbon steel reinforced concrete once corrosion has initiated. However the duration of the corrosion propagation period could be significantly longer depending on the exposure environment concret cover and concrete composition (e.g. w/cm total cementitious content supplementary cementitious presence). A better understanding on how corrosion propagates could give better guidance when conducting the assessment and control of corrosion for structures in which corrosion has initiated. Corrosion propagation was investigated on instrumented reinforced concrete pipes after corrosion of the reinforcement had initiated. Two types of concrete compositions were investigated. No chlorides were present initially in the concrete. Chlorides were transported into the concrete via migration using a set-up similar to what is usually used for chloride electrochemical removal but with the opposite polarity. Once corrosion initiated the electric field was removed and the specimens exposed to lab humidity and temperature for about 100 days during this time corrosion naturally continued. It was decided to apply a current equivalent to 1 ?A/cm2 via a galvanostat (in some cases this current was later increased to 2 and 5 ?A/cm2). The applied current density assumed that half of the steel area under the reservoir was undergoing corrosion. The current was applied cyclically: typically 11 days on and then disconnected for 3 days. The specimens during this period were stored in high humidity and after several cycles selected ones were covered with saturated sand while others remained under the high humidity exposure. During the disconnected periods electrochemical techniques such as corrosion potential linear polarization resistance electrochemical impedance spectroscopy were performed the latter two test at least two days after disconnection. Selected specimens were terminated and gravimetric weight loss measured. These weight loss values were correlated to the mass loss calculated by using Faradays law.