Steel Corrosion Induced by Chloride or Carbonation in Mortar with Bending Cracks or Joints

Shin-ichi Miyazato and Nobuaki Otsuki Journal of Advanced Concrete Technology, 8(2) 135-144, 2010 Steel in concrete may corrode due to chloride or carbonation especially at cracks and joints. The objective of this study is to experimentally investigate comprehensively the pattern of corrosion cell formation (macrocell and microcell) as well as the corrosion rate using mortar specimens with defects simulating cracks and/or joints. The three important factors are listed as follows: 1) supply position of chloride ions or carbon dioxide, 2) environmental conditions, and 3) water-cement ratio of mortar. The results indicate that, in the case of chloride induced corrosion, decreasing the water-cement ratio (0.3) increased the activity of macrocell prominent corrosion. On the other hand, increasing the water-cement ratio (0.7) increased the activity of microcell prominent corrosion. Therefore, in the presence of defects, a high corrosion rate might be promoted even at a low water-cement ratio. The study also reveals that, in the case of carbonation induced corrosion, macrocell prominent corrosion occurred regardless of the water-cement ratio, and the lower the water-cement ratio, the lower the corrosion rate. Finally, the study proves that the corrosion rate induced by chloride was higher than that induced by carbonation.

It has been shown that cracks are most often at the origin of damage and necessary repair measures in practice. But in durability design cracks are not even mentioned. This paper clearly points out the deteriorating mechanisms of cracks. As cracks can hardly be avoided in practice, results of this paper will help to build more durable reinforced concrete structures in the future. (Prof. F. H. Wittmann, Aedificat Institute Freiburg, Germany)