On the Caribbean coast, the biggest threat to a concrete structure is not the earthquake: it is the breeze. Sea air carries chlorides that work their way into the concrete little by little until they reach the reinforcing steel. When the concentration passes a threshold, the layer that protects the steel breaks down and corrosion begins.
Rust takes up several times the volume of the original steel. That expansion cracks the cover, the concrete spalls and the steel is left exposed. It is the damage you see in so many buildings more than thirty years old near the sea.
What to specify
The NSR-10 classifies chloride exposure and, for it, limits the water-cement ratio and sets a minimum concrete strength. In practice, three decisions make the difference: a low-permeability concrete, generous cover and good curing.
Cover is the cheapest decision and the easiest one to lose. A badly placed spacer takes away on site the centimeters that were designed. That is why supervision measures cover before every pour, not after.
Frequently asked questions
Why does steel corrode near the sea?
The sea breeze carries chlorides that penetrate the concrete; when they reach the steel they break down its protective layer and corrosion begins.
How is it prevented?
With a low-permeability concrete, generous cover that is well controlled on site, and good curing.
