Rishabh LalaDual Degree RGPV, Bhopal

CORROSION OF RE-BARS

INTRODUCTIONCORROSION PROCESSCORROSION EVALUATIONTYPES OF CORROSIONPROTECTION METHODS CONCLUSION

OUTLINE

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

CHLORIDE INDUCED REINFORCEMENT CORROSION IN CONCRETE EXPOSED TO SEAWATER

Corroded rebar from cracked concrete of a parking structure exposed to de-icing salts

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

VOLUME CHANGE

VOLUME

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 ?

(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 ?

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?

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

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

CORROSION EFFECTS

Abandoned Electric Pole

(Shyamla Hills)

REBAR COATING

FLY ASH

HOT-DIP GALVANIZING

SENSORS FOR MONITORING CORROSION

EFFECTIVE COVER

PREVENTION OF CORROSION

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