Development Of Corrosion-induced Crack And Distribution Of Rusts In Reinforced Concrete Structures With Rebar Corrosion

Steel corrosion in concrete is a major cause of durability problems for reinforced concrete structures. As the steel corrodes, it produces tensile stress on the surrounding concrete because of volume expansion, then cracks in the concrete cover occur. As a result, the bearing capacity and durability of concrete structures will be threatened seriously, leading to spalling of the concrete cover. Different from normal concrete, because of complicated interfacial transition zones and microcracks in recycled aggregates, the use of recycled aggregates will have more complex influence on cracking progress in concrete. Different percentage of recycled aggregates may have different cracking progress. This paper focuses on the mechanism of corrosion-induced cracking progress and the distribution of rusts in normal concrete and recycled aggregate concrete by experimental studies. The main work in this paper can be summarized as follows:(1) Four types of recycled aggregate concrete and a normal concrete specimen of Hangzhou bay cross-sea Bridge were investigated to study the mechanism of the corrosion-induced cracking progress. The total circumferential crack width at different radius, the total crack length, the total crack area and the total crack width at the surface of the concrete cover were measured by digital microscope. The model of corrosion-induced cracking progess of different concrete specimens was established, the physical meanings of the parameters of the model were studied as well. The differences of the corrosion-induced cracking progesses among the different concrete were discussed by contrast.(2) Four types of recycled aggregate concrete were investigated to study the distribution of corrosion products at the steel/concrete interface. The interface and corrosion-induced cracks were observed and measured by SEM in BSE mode. The relation of corrosion layer thickness (TCL) and thickness of corrosion-filled paste (TCP) was studied. The influence of the inner cracks on the development of TCP was also discussed. Based on the study above, a corrosion-induced cracking model considering the rust distribution at the steel/concrete interface was proposed to describe the concrete cracking progress induced by steel corrosion, instead of the two-stage cracking model.(3) A reinforced concrete specimen of Hangzhou bay cross-sea Bridge that had deteriorated in an artificial environment for two years was investigated to study the mechanism of distribution of corrosion layer. The thickness of corrosion layer at the steel/concrete interface was measured by SEM in BSE mode. The non-uniform distribution of corrosion layer was presented by a Gaussian fuction in polar coordinate system. Besides, the mathematical and physical meanings of the parameters in the model were studied, and the relation between the location of rust peak and corrosion-induced cracks was also discussed. According to the study above, the developed Gaussion model was established.