The main reason behind the collapse of buildings is not an earthquake but the expansion of steel due to corrosion, by up to three times its original diameter. Corrosion causes fatigue crack propagation in structural steels. The development of pitting corrosion introduces additional points of stress concentration at which cracking may develop, which will reduce the fatigue strength. Steel also expands when subjected to changes in temperature. When free to deform, this impacts concrete structures due to fluctuations in temperature. The size of the concrete structure whether it is a bridge, a highway, or a building does not make it immune to the effects of temperature. This occurs regardless of the structure’s cross-sectional area. Galvanized TMT rebars address this issue. These are coated TMT rebars with a protective layer of zinc (Zn) metal. The coating is usually carried out by a hot-dip galvanizing process. It is a corrosion protection process that results in metallurgical bonding by completely enclosing the steel & sealing it from the corrosion impact of the atmosphere, without any effect to the properties of steel. This Process is secure & reliable and has emerged technically superior and cost-effective in the long run. It increases the life of the TMT Bars.
Hot- dip galvanization method of TMT rebars
Hot-dip galvanizing is a total immersion process where the steel element is dipped into a bath of molten zinc. Unlike metalizing, galvanizing metallurgically bonds the zinc to the steel substrate making it a part of the steel, not a coating. The alloy layers in the coating are harder than the base steel resulting in a coating that is not only firmly adhered to the steel but is tough and hard and can resist abrasion and fairly heavy handling.
Due to its unique metallurgical bond, a galvanized coating is incredibly tough, offering exceptional performance across multiple layers. An initial outer layer provides reliability as a buffer zone, helping to absorb any initial shock to the coating. Underlying zinc-iron alloys can be harder than mild steel itself, and will further reduce any potential penetration of the coating or the exposure of bare steel. This means that a galvanized coating is highly chip resistant and particularly suited to areas of high-frequency industrial wear. The bond between concrete and the rebars is essential for developing the full capacity of the reinforcement. The single largest contributor to the bond between the rebars and the concrete is whether the rebars are ribbed or plain.
Galvanized TMT Rebars must comply with Indian Standard IS: 12594- 1988 which is approved by the Indian Government.
Advantages of Galvanized TMT Rebars
Galvanized TMT rebars provide three-way protection for structures namely, physical barrier, cathodic and sideways creep protection. It comes with several advantages as given below.
- Durable, offering an average coating thickness of 85 microns
- Galvanized coating provides cathodic protection to the steel against climatic conditions
- Remains unaffected by UV ray exposure during field storage and installation period
- Offers equal or better bond strength in concrete not requiring any additional lap lengths
- Provides barrier against corrosive environment, which is three times more than normal steel
- It can be used without special equipment and can be fabrication after galvanization
- Provides superior strength and coverage
- Galvanizing has an abrasion resistance up to ten times better than organic paint coatings
- Tolerates higher chloride concentration
- Delay the onset of cracking and spalling
- It is cost-effective varying according to different geographical location
- Better protected during storage and construction before placing
- Structural protection against chloride contamination
- Reduces surface staining opportunities
- Control chloride ion diffusion in concrete
- Offers protective barrier against the contact if chloride ions and steel
Applications of Galvanized TMT Rebars
Galvanized TMT Rebars can be used widely in a variety of reinforced concrete structures such as;
- Bridge decks
- Surface exposed beams and columns
- Exposed slabs
- High-risk structures
- Coastal and marine structures
- Towers
- Airports
Infrastructure development today needs to keep pace with the demand of the new world to sustain the current impacts of nature & polluted environment. Iron & steel is the most important material for infrastructure development. Unless protected, it will corrode & lead to the weakening of structures. Galvanized steel is the best way to build an environmentally sustainable, cost-effective & long-lasting structure.
