Understanding Concrete Carbonation
To ensure the ongoing quality and performance of concrete structures, one must check its condition by means of structural surveys, for example a HOKLAS concrete test for carbonation depth.
On a basic level, carbonation occurs when the calcium hydroxide in cement reacts with carbon dioxide in the air. The impact is to decrease how porous the concrete is, which has a hardening effect that can make the material stronger and more tensile. However, while this may not be an issue in non-reinforced concrete, and actually a positive, it can be destructive and dangerous with reinforced concrete.
Carbonation reduces the pH level of concrete and this greater acidity has a negative effect on the efficacy of the protective layer that stops the steel reinforcements from being corroded. Rusted metal expands the concrete, and the result is instability, less durability and crumbling concrete. For the environment and in terms of safety, carbonation needs to be discovered and dealt with as early as possible.
Drilling and using a special indicator is one way in which the depth of carbonation can be detected, with colour changes happening where there are issues. By testing for carbonation one can help to guard against potential future issues. This can save time and money in the future, as issues can become far greater if a problem is not discovered until real damage is already done.
In Hong Kong and other tropical climates, this test is particularly important as humidity acts like a catalyst on cement carbonation. The heat doesn’t help matters, either. Building facades exposed to the elements are often the first parts of buildings to suffer from corrosion. When cracks appear, this exacerbates the problem, with more carbon dioxide leaking and lowering alkalinity. The result can be a structure that becomes in a state of major decline.
Concrete issues can equate to structural problems that need immediate action at some point, albeit the process of carbonation is relatively slow, at a rate of 1 mm per year on average. Once the depth of the carbonation is identified, steps can be taken to repair the damage, such as removing the corrosion and any loose concrete, plus protective measures.