Corrosion of reinforcing steels at cracks in concrete

The purpose of the research was to study to what extent the reinforcements in concrete bridges were corroded at cracks and which factors had the greatest influence on corrosion of reinforcements. In all, 48 road and railway bridges in different parts of Finland served as objects of investigation. In the field of investigation, the corrosion grade of reinforcing steels at cracks was visually estimated and the depth and width of a corroded area was measured. The factors chosen to explain corrosion were: the age of a bridge, the thickness of a protective concrete cover, the crack width, the carbonation depth at crack and at uncracked concrete surfaces, the pH value of concrete in the vicinity of reinforcements as well as the strength and chloride content of concrete. The correlation of the corrosion grade with the pH and chloride content of concrete could be clearly indicated. The corrosion grade was also proved to be dependent on the difference between the thickness of the protective concrete cover and depth of the carbonated zone at the crack. The carbonation depht at crack can be estimated by means of the crack width. The correlation with the quantity 100 neliöjuuri w, where w is the crack width in millimeters, was noticeable. In the bridge design, a potentially dangerous crack size can be estimated from the formula S - 100 neliöjuuri w <- 0. where S is the thickness of the protective cover for reinforcement.