Corrosion of re bars
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Transcript of Corrosion of re bars
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Rishabh LalaDual Degree RGPV, Bhopal
CORROSION OF RE-BARS
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INTRODUCTIONCORROSION PROCESSCORROSION EVALUATIONTYPES OF CORROSIONPROTECTION METHODS CONCLUSION
OUTLINE
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Serious problem called rust – Bridges of steel
22.6$ Billions – average cost in 2009 – US
Corrosion in India – Railways, Dilapidated Buildings
Reduces the strength of material
CORROSION A SERIOUS PROBLEM
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CHLORIDE INDUCED REINFORCEMENT CORROSION IN CONCRETE EXPOSED TO SEAWATER
Corroded rebar from cracked concrete of a parking structure exposed to de-icing salts
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ASTM terminology (G 15) defines corrosion as “The chemical or electrochemical reaction between a material, usually a metal, and its environment that produces a deterioration of the material and its properties.”
For steel embedded in concrete, corrosion results in the formation of rust which has two to four times the volume of the original steel and none of the good mechanical properties. Corrosion also produces pits or holes in the surface of reinforcing steel, reducing strength capacity as a result of the reduced cross-sectional area.
DEFINITION
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VOLUME CHANGE
VOLUME
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Yes if:
(a) For dry Concrete – no H2O to form rust. Also aggressive agents cannot easily diffuse into dry concrete.
(b) Avoiding Oxygen Contact – Sufficient Cover
(d) A Polymeric Coating is applied to the concrete member to keep out aggressive agents. These are expensive and not easy to apply and maintain.
CAN CORROSION BE AVOIDED ?
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(e) A polymeric coating is applied to the reinforcing bars to protect them from moisture and aggressive agents. This is expensive and there is some debate as to its long- term effectiveness.
(f) Stainless steel is used in lieu of conventional bars. This is much more expensive than conventional bars.
CAN CORROSION BE AVOIDED ?
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No, Not entirely !
Concrete is not usually under water or continuously dry. Aggressive agents such as carbon dioxide, de-icing agents and/or sea water can diffuse into the best of moist concrete, and corrosion will eventually result.
CAN WE AVOID CORROSION?
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Depth of carbonation can be detected using an indicator.
A chemical such as Phenolphthalein sprayed on to freshly broken concrete.
Areas remaining alkaline will turn in a bright purply-pink color.
Carbonated areas of concrete will remain unchanged in color.
DETECTING CARBONATION
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Best method to detect corrosion of rebars
Measuring the potential of embedded bars relative to reference of the potential half cell placed on the concrete surface
Concrete functions as the electrolyte
Corrosion is calibrated to the measured potential difference
HALF POTENTIAL CELL
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CORROSION EFFECTS
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Abandoned Electric Pole
(Shyamla Hills)
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REBAR COATING
FLY ASH
HOT-DIP GALVANIZING
SENSORS FOR MONITORING CORROSION
EFFECTIVE COVER
PREVENTION OF CORROSION
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CORROSION IS UNDESIRABLE FOR THE DURABILITY OF THE STRUCTURE
CAUSES INCLUDE MOISTURE + CO2 FROM ATMOSPHERE, CHLORINATION AND CARBONATION
MEASURES SHOULD BE TAKEN TO PREVENT CORROSION AT RIGHT TIME
KEY TAKE-WAYS