Critical Corrosion Amount to Cause Cracking of Reinforced Concrete Structures

The corrosion of a steel bar in concrete induces expansion pressure and thus causes tensile stresses in surrounding concrete. This may cause serious cracking in concrete cover, which greatly affects the serviceability and durability of concrete structures. Therefore, it is necessary to realistically determine the critical corrosion amount (CCA) that causes the initiation of cracking in concrete cover. The purpose of this study is to explore and determine the CCA that causes surface cracking of concrete cover. To this end, a comprehensive experimental study was conducted. Major test variables include concrete strength and cover thickness. The corrosion tests of steel bar in concrete have been conducted, and the strains on the surface of concrete cover have been measured according to various amounts of steel corrosion. The CCA, which causes the initiation of cracking on the surface of concrete cover, was determined from the present test results. It was seen that CCA increases greatly with an increase of cover thickness of concrete. The present study indicates that CCA increases approximately proportionally to the square of concrete cover thickness. The concrete strength also affects CCA. It can be seen from this study that CCA increases with an increase of compressive strength, especially in the case of normally used medium and large cover thicknesses, that is, for a cover thickness above 40 mm (1.6 in.) in actual concrete structures. It was found, however, that the effect of the compressive strength on CCA is not large for small cover thickness such as 20 mm (0.8 in.). The present study may provide a good base for future development of realistic durability design and service-life assessment of concrete structures. [PUBLICATION ABSTRACT]