Concrete is one of the most widely used building materials in the world. It is a versatile, durable, and affordable material that is used in the construction of everything from buildings to bridges. However, like all materials, concrete has its limitations, and one of these limitations is the issue of carbonation.
Carbonation is a natural process that occurs over time, when carbon dioxide in the air reacts with the concrete causing a decrease in its pH level. This makes it more acidic, which over time can weaken the concrete and cause it to crack. This isn’t because carbonation makes the concrete weaker; as the pH of the concrete decreases, the steel reinforcement within the concrete can become corroded (due to a breakdown of it’s ‘passive layer’). This corrosion causes expansion, which can cause the concrete covering the steel to crack and fail.
Concrete carbonation occurs faster in the presence of moisture, so it is more common in humid or wet environments. It is also more likely to occur in structures that are exposed to the elements, such as bridges and tall buildings, than in structures that are protected from the weather.
Preventing carbonation
In many cases, carbonation can cause no damage to concrete if the depth if the reaction hasn’t made it to any exposed reinforcement. The ‘depth of cover’ to any steel must be carefully controlled during construction, to reduce the risk of issues in future; cover of less than 50mm is usually considered a concern, but this may need to be thicker for more exposed or vulnerable areas.
To further prevent concrete carbonation, designers can take a number of steps. One of the most effective ways to prevent carbonation is to use concrete with a low water-to-cement ratio. This reduces the amount of water in the concrete and can significantly slow the rate of carbonation.
Another way to reduce the risk is to use an anti-carbonation coating. Most products as as a carbon dioxide barrier, preventing the reaction and change to PH level from occurring.
Repair Options
Concrete carbonation can be a serious issue, but it can be addressed with adequate inspection and repair. Inspecting for carbonation typically involves a visual inspection and ‘tap test’, as well as drilling core hole samples into concrete which are then tested to determine the depth of carbonation.
If carbonation is found, there are a number of repair methods that can be employed. One of the most common methods is to apply a cementitious coating to the surface of the concrete. This coating can help to slow down the carbonation process and protect the concrete from further damage.
Small areas affected by carbonation can be repaired by removing any corrosion to exposed steel, treating the steel and applying a repair mortar to protect it from further issues.
Another method is to use a chemical treatment to neutralize the acid in the concrete. This involves applying an alkaline solution to the surface of the concrete, which can help to raise the pH of the material and reduce the effects of carbonation.
In extreme cases, it may be necessary to remove and replace the damaged concrete. This can be a costly and time-consuming process, but it may be necessary if the damage is extensive.
Concrete carbonation is a natural process that occurs over time as carbon dioxide in the air reacts with the calcium hydroxide in concrete. Whilst carbonation is a natural process, if left uncontrolled it can have severe implications on the structure of a building. Builders and designers can prevent carbonation by ensuring that materials used are adequate for their environment, and that any exposed areas are properly protected. By taking these steps, builders can ensure that their structures remain strong and durable for years to come.
If you suspect you have issues with your property and need advice, feel free to Contact Us.