1991 Fiscal Year Final Research Report Summary
Relationships between and cracking and corrosion of steel in concrete structure
| Project/Area Number |
02650401
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
Building structures/materials
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| Research Institution | Osaka University |
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Principal Investigator |
OHNO Yoshiteru Osaka University, Faculty of Engineering, Associate Professor, 工学部, 助教授 (30029194)
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| Project Period (FY) |
1990 – 1991
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| Keywords | Macrocell corrosion / Cracking, / Cover thickness / Water cement ratio, / Casting direction / Corrosion current / Half cell potential / Polarization resistance |
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| Research Abstract |
Experiment 1: The effects of cover thickness, water cement ratio and casting direction on macrocell corrosion of steel in concrete was investigated by electrochemical and electrical methods. Steel (anode) embedded in 1% Cl^- contaminated concrete was electrically connected to stainless steel plate (cathod) embedded in Cl^- contaminated concrete. The specimens were subjected to repeated cycles of one day wetting in 3.27 %NaCl solution and one day drying in natural environment.
It was found that : 1) cover thickness over anode steel has effects on the macrocell corrosion degree of steel anode in Cl^- contaminated concrete, 2) water cement ratio considerably influenced corrosion, 3) corrosion of steel in concrete cast horizontally was remarkably higher than that in concrete cast vertically due to bleeding of concrete.
Experiment 2: The effects of cover thickness, cracking, water cement ratio and casting direction on macrocell corrosion of steel in concrete was investigated by a accelerated
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corrosion test using reinforced concrete beam specimens. In order tomeasure macrocell corrosion currents, reinforcing steels were coated with epoxy resin films, leaving only 27 mm zone (anode) in the center unprotected. The steel was connected electrically to stainless bars (cathod) set near the steel (Fig.1). Beam specimens were loaded to introduce cracks of defined width and subjected to 35 repeated cycles of one day wetting in 65 ﾟC, 3.2 % NaCl solution and one day drying under room environment. The electrochemical characteristics and corrosion deteriora lion were also measured. It was found that : 1) The electrochemical characteristics coincided with change of corrosion currents, and it is possible to judge undestructively the condition of corrosionof steel in concrete. The integration of the reciprocal of polarization resistance related to the degree of corrosion.
2) As cover thickness was large and crack width was narrow, the degree of corrosion decrease.
3) Low water cement ratio concrete inhibited remarkably corrosion. Effects of cover on corrosion was large in w/c 60 % concrete and effects of crack was large in w/c 40 % concrete.
4) The casting direction of concrete had not effect on corrosion of steel. Less
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