Corrosion of Steel Bars in Cracked Concrete: Very Beginning to the Early Age of Exposure


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Title: Corrosion of Steel Bars in Cracked Concrete: Very Beginning to the Early Age of Exposure

Author(s): T.U. Mohammed and H. Hamada

Publication: Special Publication

Volume: 235


Appears on pages(s): 103-124

Keywords: corrosion; crack; macro-cell; marine environment; micro-cell; slag cement; steel bar

Date: 3/22/2006

The progress of macro- and micro-cell corrosion of steel bars in cracked concrete from the very beginning to early age exposure was investigated under an artificially created marine splash environment. For this, concrete prism specimens (100 × 100 × 600 mm) were made and cracked in the laboratory. The investigated parameters were crack widths (different stress levels); cement types (ordinary portland and slag cements); and surface condition of the bar (polished and cement paste coated). Electro-chemical and physical evaluations of corrosion, chloride contents in concrete, and the deposits in the cracks and the de-bonded area beside the crack were investigated. Natural seawater was sprayed over the specimens to simulate the marine splash environment. A remarkable amount of macro-cell corrosion is generated over the steel bar at the cracked region immediately after seawater spray. However, it drops gradually and no significant influence of seawater spray is found later. The magnitude of micro-cell corrosion is very low compared with the macro-cell corrosion at the early age, however,, it increased gradually. The deposits over the steel bars at the cracked region (i.e. de-bonded area) and onto the cracked planes are confirmed as CaCO3 and ettringite. Pitting is observed for wider cracks. At the wider cracks, relatively larger corrosion pits are found for slag cements. Application of a cement paste coat over the steel bars is found to be an effective way to control corrosion at the cracked region.