Deteriorating concrete structures are a major problem around the world. Largely attributed to the corrosion of steel reinforcement, concrete structures built to last 50 to 100 years routinely need substantial repairs and rehabilitation during their service life. Preventing concrete corrosion is an important part of planning a concrete structure.
How Corrosion Happens
Concrete normally provides reinforcing steel with excellent corrosion protection. However, this protection can break down over time by coastal environments and deicing chemicals. Once the passive layer is compromised, steel reinforcement can corrode.
Concrete’s ability to resist corrosion depends largely on the permeability of the concrete and the thickness of concrete cover over the reinforcement. However, if cracks are present, aggressive agents can quickly reach the depth of the steel and initiate corrosion.
Traditional measures to mitigate corrosion have proven to be less effective than desired.
- Excessively thick concrete cover over the reinforcing steel is vulnerable to cracking
- Corrosion inhibitors such as calcium nitrite provide only temporary protection
- Epoxy coated reinforcement has proven unreliable in field applications
The problem is these systems do nothing to prevent the conditions that cause corrosion from developing in the first place.
In all cases, the penetration of water into concrete is a critical factor in the corrosion of steel reinforcement. Water acts as a carrier for chloride ions and is also required for corrosion to occur.
Therefore, the first line of defense against corrosion is to prevent the penetration of water.
It is important to use a concrete mix with low permeability and to use an appropriate amount of concrete cover for the application. Additionally, the concrete should be placed, consolidated and cured following ACI guidelines to minimize shrinkage and cracking. With good materials and workmanship, concrete can resist the development of corrosive conditions, which increases the durability of structures and reduces lifetime maintenance costs.
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