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Understanding Corrosion Effects on Steel Reinforcements in Concrete

1. Carbonation and chlorination: loss of alkalinity due to organic or carbonic acids, or being subjected to chloride ions present in the vicinity can induce the corrosion process.

2. Cracks and gaps: this is a no-brainer. Any break or crack in the concrete that reach deep enough to expose the steel to the outside air and water will leave the reinforcement vulnerable to oxidation.

3. Moisture pathways: if the concrete is not of good quality, it can become more or less porous in nature when solidified. Not only this reduces the effective strength of the pile or column, this also allows moisture from the atmosphere to crawl through the microscopic gaps in the concrete and bring fresh acids from outside to eat away the steel within. For this reason, a concrete structure looking perfectly from outside may have rusted steel bars inside.

4. Insufficient cover: if the design did not allow the concrete or the passivation to blanket the steel properly, then there will be exposed places that would be endangered by the atmospheric corrosion effects.

Effects of Corrosion on Steel Reinforcements:

When corrosion takes place on the steel reinforcements within a concrete assembly, the member may display the following effects that may become apparent gradually over time:

1. White patches: not directly a result of steel corrosion, this is actually a deterioration of the concrete member itself. The white patches are basically calcium carbonate (CaCO3) which is a product of the calcium hydroxide present in the cement and the carbon dioxide in the air.

2. Brown patches: seen along the lines of reinforcement, these are iron oxide stains carried to the surface of the structure from the corroding steel underneath, via moisture pathways.

3. Cracks: The byproducts of the corrosion process, i.e. the salts or oxides, occupy more volume than the steel that it was formed from. Thus these new materials create pressure on the cementing surrounding it, and just like a root through a rock, can split it asunder, given enough time.

4. Concrete Spalling: when the salts or oxides are formed, they negate the bond between the concrete and the steel, peeling the concrete off like onion layers.

5. Bar snapping: a steel bar weakened by corrosion obviously won?t be able to bear the tensile strength exerted on it as normal. After a given time, it will break under pressure.

6. Buckling bars: in the last stage in the demise of a concrete member, the snapping of bars and spalling of concrete will lead to a bulging of concrete in that area, weakening it severely enough so that the whole member collapses.

Remedies of Corrosion in Steel Reinforcements - As in everything, using better materials and periodically checking the structure thoroughly can lead to preventing, or at least, delaying the corrosion of the steel within the structure. Here are some pointers:

1. Sufficient cover: As long as there are good thick concrete and other passivation materials over the steel, it cannot come into contact with the weather or even if it does, there will be enough alkalinity there to reduce chances of corrosion.
2. Concrete quality: when you use high-quality concrete and good water/cement ratio, it will help keep the steel bars within properly alkalinized and also reduce the chance of forming moisture pathways.
3. Proper Compaction: the concrete must be properly and thoroughly compacted so that the chances of crevice forming is reduced. Skilled staff should be able to do that.
4. FBEC Bars: The use of Fusion-Bonded Epoxy Coated steel bars are coated with a thermoset polymer epoxy resin which can seriously reduce the chance of corrosion.
5. Cement Polymers: some specific substances can increase the alkalinity of the concrete that reduces the risk of corrosion.
6. Corrosion inhibitors: Spreading migratory corrosion preventives over the concrete can reduce the risk of further corroding a steel bar within the concrete. Chemicals like Calcium Nitrite are best at seeping through the cement to reach the steel and inhibit the corrosion locally.

In combination, these methods and constant vigilance can save a lot of lives and property damage.

Understanding Corrosion Effects on Steel Reinforcements in Concrete