This report describes laboratory investigations of factors affecting the corrosion risk of reinforced concrete road bridges. The work was carried out under contract to TRRL over the three years from January 1983 to December 1985. Full details of the experimental techniques and all the results obtained through the three year period have been presented in a final report (see IRRD 802250). Cement paste and concrete specimens prepared during 1983 have been maintained and monitored in order to study the effects of (i) chloride ions introduced post-hydration by various methods, (ii) chloride ions introduced pre-hydration in the mixing water and (iii) cycles of carbonation. The specimens exposed to external sources of chloride ions have been tested at six, twelve and twenty four month exposure times by means of the 'crush-sectioning' and pore solution expression techniques described previously. Specimens containing internal chloride ions and a small number of cores obtained from bridge decks have also been examined with the aid of pore solution expression. The regular monitoring of parallel specimens containing embedded steel electrodes by means of corrosion potential and polarisation resistance measurements has been maintained throughout the period. A corrosion measurement system based on electrochemical noise has been developed, the aim of this work being to evaluate the potential of the technique as an on-site method for the prediction of reinforcement corrosion rates. The data that has been obtained will have applications in the appraisal of corrosion risks in reinforced concrete road bridges since it will permit better definition of the threshold level of the ratio of concentrations (free chloride to free hydroxyl ion) required to depassivate steel in concrete.

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