Concrete carbonation is usually associated with the issue of shrinkage and the corrosion of steel reinforcements used in concrete structures. However, not all the effects of concrete carbonation are entirely bad. Before we take a closer look at the impact of concrete carbonation and how to detect it, let’s take a moment to explain how it’s caused.
What is carbonation in concrete caused by?
Concrete is naturally a highly alkaline material. For concrete structures that use steel reinforcement bars to increase tensile strength, the alkaline strength of the concrete protects the steel from corrosion by providing a passive resistive layer. However, when concrete is exposed to carbon dioxide and other pollutants in the air, carbonation can occur.
Carbonation occurs when CO2 comes into contact with the water in cement. When this occurs, carbonic acid is formed, and this neutralizes the alkaline state of the concrete. Once this happens, carbonation moves from the surface of the concrete towards the centre of the concrete where it can reach the steel reinforcement bars.
How is concrete carbonation assessed?
The carbonation of concrete is assessed using an alkalinity indicator, such as phenolphthalein. This is used to work out the PH level of the concrete in order to establish the extent of the carbonation and its proximity to the steel.
What is the impact of concrete carbonation?
Corrosion: As we’ve mentioned, one of the most damaging effects of concrete carbonation is the corrosion of steel reinforcements in the concrete structure. This is caused by the alkaline strength of the concrete being disrupted.
Shrinking: The reduction of the concrete’s PH level can also cause shrinkage. This may lead to cracking or warping.
Increase in compressive strength: As counter intuitive as it may seem, the reaction caused by carbonation also increases the compressive strength of concrete. However, it’s important to emphasise that the damaging effects of concrete carbonation can outweigh this benefit, which is why it’s important to prevent the process as much as possible.
What factors affect the rate of concrete carbonation?
The carbonation process may be sped up/ slowed down by the following:
- Grade of the concrete
- Water cement ratio
- Permeability of the concrete
- Surface protection
- Age of the structure
- Porosity of the concrete
- Curing period
Can it be prevented?
Whilst carbonation is a natural reaction that occurs when concrete is exposed to CO2 in the environment, it can be slowed down by the following:
- Lower water-cement ratio
- Adequate/ extended curing period. This reduces the permeability of the concrete which helps to slow down the rate of carbonation.
- Use of protective coatings
At Al Manaratain, all our concrete products are manufactured to be durable and long lasting to ensure that they can withstand environmental wear as far as possible. For more information, please don’t hesitate to get in touch with us.