The last blog described the universal problem affecting the RCC which is corrosion / rusting and what are the causes of corrosion. In order for a Reinforced structure to have corrosion, the presence of these two components is needed which is moisture and air. Usually, corrosion starts out slowly and results in severe damages which in turn affects the structural integrity of the building.
Stages of Damage
When corrosion starts to kick in, it will end in the eventual destruction of the structure. The corrosion process is classified into several stages.
- White patches: When moisture content builds up inside the reinforcement concrete, carbon dioxide reacts with calcium hydroxide in the cement paste to form calcium carbonate salts. As moisture migrates up to the surface of the concrete, it carries the calcium carbonates towards the surface and reacts with carbon dioxide to forms white patches.
- Brown patch formation: The next stage in corrosion is the formation of brown color patches. This results when a ferric oxide layer is formed on the reinforcement surface. This brown product resulting may permeate along with moisture to the concrete surface which results in cracks shortly after.
- Formation of cracks: When corrosion happens, it results in more volume. Increase in volume creates considerable pressure on the concrete which results in cracking. Hairline cracks start to appear which indicates the corrosion of reinforcement. As corrosion progresses, there will be a formation of multiple layers of ferric oxide on the reinforcement which in turn exert considerable pressure on the surrounding concrete resulting in wider hair cracks. The bond between concrete and the reinforcement is considerably reduced.
- Spalling of the concrete: As the bond between the steel and the concrete decreases due to the formation of oxide layers, the concrete starts falling off, such that it results in the overall reduction of the size of the structure and exposing of reinforced steel.
- Breaking bars: Further spalling of the concrete leads to the eventual breaking of the steel bars. Around this stage the collapse of the structure is imminent.
Corrosion, even though it starts as a small slow process, it results in big irreversible changes to the building structure, loss of hard earned money, resources and more. Corrosion is something that can be delayed to an extent by using appropriate measures, but once it kicks in, there’s nothing that can be done to reverse the damages caused by it.