Macro- and Micro-Cell Corrosion of Steel Bars in Cracked Concrete made with Various Cements

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Title: Macro- and Micro-Cell Corrosion of Steel Bars in Cracked Concrete made with Various Cements

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

Publication: Special Publication

Volume: 221

Issue:

Appears on pages(s): 51-72

Keywords: chloride; corrosion; cracked concrete; fly ash cement healing; marine environment; ordinary portland cement; slag cement

Date: 5/1/2004

Abstract:
Macro- and micro-cell corrosion of steel bars in pre-cracked prism specimens ex-posed to marine environment for 15 years are summarized here. The size of the specimens was 100xlOOx600 mm. W/C were 0.45 and 0.55. The specimens were made with ordinary portland, slag (Types A, B and C), and fly ash (Type B) cements. A round steel bar of diameter 9 mm was embedded at the center in each specimen. Crack widths were varied from 0.1 to 5.0 mm. Chloride concentrations in the concrete, micro- and macro-cell corrosion, passivity grade, anodic polarization curve, deposits in the crack, and pit depths over the steel bars were investigated. Dense microstructure of concrete made with a large amount of slag (SCB, SCC) causes accumulation of more chloride in the vicinity of the unhealed cracks (>0.5 mm). However, it does not lead to a remarkable amount of corrosion at the cracked region compared to the other cements after 15 years of exposure. Narrower cracks (5-0.5 mm) as well as the debonded areas in the vicinity of the root of the crack over the steel bars heal irrespective of the cement types. It improves the passivity of the steel bar at the cracked region. Relations between pit depth and crack widths; and macro-cell and micro-cell corrosion are proposed.