Silver steel turns brown if left unhindered in the atmosphere is something every one of us has seen, somewhere or the other. The hindrance to this corrosion is concrete. Concrete creates an optimum pH range around the steel which protects the steel from corrosion. But still they corrode mainly in marine and coastal environment and the corrosion of steel bars inside concrete is especially problematic as rust has a higher volume than steel. This results in cracking and even breaking of the concrete from the surface.
Corrosion happens mainly when the water leaches down the surface and either it reacts with acidic gases like CO2 or SO2, or the high amount of chloride admixes.
Which TMT is appropriate for your project?
|Structure type||Environment||Exposure conditions||TMT bars to be used|
|Super-structure||Mild||Aggressive conditions, except|
those situated in coastal area.
|TMT + Corrosion Inhibitors|
|Moderate||Surfaces sheltered from severe|
rain but remains wet
except water with marine salts.
|TMT + Corrosion Inhibitors, CRS or FBEC|
|Severe||Concrete surfaces exposed to severe|
rain or Completely immersed in seawater
or coastal environment
|CRS(all areas), FBEC(Buildings)|
|Extreme||Surfaces exposed to Corrosive fumes, liquid or solid aggressive chemicals||CRS|
|Structures to retain water (like tanks)||-||-||Zinc Coated|
FBEC rebars(Fusion bonded epoxy coating)-An epoxy powder is first clung by electrostatic charges with a hot bar. The powder melts covers and then cools to produce a well-adhered continuous protective coating. This layer provides protection to rebar against corrosion. It is very useful for the protection against chloride ion.
CRS (Corrosion resistance steel) rebars– Elements like Copper, Chromium & Phosphorus are blended while making the bar itself. They are the most useful rebars we have for protection against severe environmental condition for superstructures. A Cu-Cr TMT rebar is 1.5 to 1.9 times more corrosion resistant than a normal TMT. Each element helps to prevent the corrosion in its own way-
- For rust to develop there must be pores. Copper plugs pores in rust and stops it from further growth.
- Phosphorus acts as an inhibitor for the reaction that form rust.
- Chromium content has improved resistance against the hollow surfaces that are created by the formation of rust.
SAIL (HCR) and TATA steel (TISCON CRS) are some of the examples of CRS rebars.
Zinc coated TMT bars-Zinc is deposited on a rebar by galvanization (deposition of zinc’s layer on a metal body by ion transfer). Coating firstly acts as a physical barrier between the source of corrosion and rebar. Even if the layer breaks, the zinc atoms around that place dissolute to protect the bar even further. The advantage of using Zinc coated bars is that flexibility is not lost during this process and bars can be easily bent or can handle roughly. SRMB Srijan Ltd. makes SRMB AZAR which is a zinc coated rebar.
TMT Re-bars + Corrosion Inhibiting Admixture– It can be used in the substructures when the soil conditions are normal and free from excess chloride and sulphates. It can be used with concrete in the superstructures in a mild environment in all except those situated in coastal areas with heavy and continuous rains and snow. A Bipolar Concrete Penetrating Corrosion Inhibiting Admixture is added in concrete as well. It doesn’t act as a barrier but slows down the corrosion process to a unnoticeable standstill. It need not be in direct contact with the steel. It’s vapour move in the concrete microstructures and stops corrosion at a microlevel.