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Issue Date: 1999
Abstract: Corrosion of reinforcements is a major cause of failure in aged reinforced concrete structures exposed to the hot humid climate in Singapore (Liam et al., 1992; Strait Times., 1989; Strait Times., 1988 ). There is little published literature available pertaining to this problem in Singapore. On-site assessment of corrosion rate of reinforcement is of great practical interest. Potential measurements were conducted on reinforced concrete structures using a copper - copper sulphate ( Cu / CuSO4 ) half cell. The potential measurement technique is an important tool in diagnosing the present and future performance of existing reinforced concrete structures exposed to corrosive environments. The objectives of this study are set in the context of the fact that a large amount of reinforcement steel in concrete is already under corrosion attack and the remaining amount will also suffer from active corrosion once the corrosion initiation period is over. Research in this area was conducted in two phases. The first part of this dissertation, phase I, was a feasibility study in which corrosion potential measurements were made on five different structures . In each structure , potential measurements were carried out on ten structural elements like columns/beams using a half cell at a regular grid interval of 300 x 300 mm over an area of 1 sq.m and the most negative potential obtained was recorded . The most negative potential reading represents anodic areas for the nodal point where corrosion is possible. Visual inspection of reinforcement for the presence of evidence of rust products, if any, at the nodal point was made by exposing a 50 mm x 50 mm area of concrete or by removing the spalling concrete for confirmation of extent of corrosion. Test areas where the negative potential vs copper sulphate electrode were more than 350 mV showed evidence of corrosion stains. No evidence of corrosion activity could be seen at locations where negative potential vs copper sulphate electrode (cse) was less than 200 mV . Thus the probability of reinforcement corrosion could be assessed by potential measurements. The results are in agreement with the predictions in ASTM standard C 876 - 91. Phase II of the study consisted of a full scale testing of carbonation, chloride content, resistivity, corrosion rate and cover of structural elements. Combining the data from the phase I and phase II studies, allowed a more consistent interpretation for all the five case studies and determination of empirical correlations between corrosion potentials and carbonation ,chloride content, resistivity , corrosion rate and cover depth . The half cell potential data for all the case studies were plotted against the respective carbonation, chloride content, resistivity, corrosion rate and concrete cover depth data. Linear regression analyses were carried for the half cell potential against carbonation, chloride content, resistivity, and cover depth data; a exponential equation was used for the results of potential against corrosion rate. Thus linear und exponential relationships could be established.
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