Influence of relative humidity and temperature on-site corrosion rates

When the steel rebar depassivates, the corrosion starts to develop at a rate which mainly depends upon the moisture content in the concrete pores. In natural outdoor exposure conditions, the moisture content will depend not only on the relative humidity of the atmosphere but also upon the temperature cycling occurring from day to night. In order to progress in the understanding of the influence of the climatic variables on the corrosion rate of real size structures, several experiments have been performed. Thus the corrosion is measured in solutions simulating the concrete pore solution and simultaneous measurement of oxygen content, Cl-/OH- ratio and conductivity were made. As well measurements in concrete specimens submitted to outdoor conditions was made. The results enable to deduce that the variation of temperature has a multiple simultaneous effect on different parameters which may counter-balance each-other. Thus the oxygen content and the pH decrease and the Cl- increase when temperature rises. The best fit of Icorr is found with resistivity.