QUP f
2w
these rebars as we as superior bend values. As a matter of fact, TMT-HCR rebars have been
found to withstand even close bend without exhibiting surface cracking. The rib pattern of
these rebars ensures excellent bond strength between the rebar surface and concrete; bond
strength attainable with such reinforcement bars fulfils the requirements of Indian specifications.
The thermally hardened TMT-HCR rebars are ideal for use in places prone to fire hazards.
Compared to conventional CTD bars, TMT-HCR rebars exhibit superior corrosion resistance
owing to the absence of torsional stresses in thermo-mechanically treated rebars and design of
suitable alloy chemistry. These rebars can be easily welded and do not require pre-heating or
post-heating treatments. These bars can also be welded with conventional CTD bars, permitting
usage independently or in combination in reinforcement structures.
The advantages of TMT-HCR rebars over conventional CTD rebars are many and include:
saving in steel, reduction in costs, enhanced strength combined with high ductility, superior
atmospheric and marine corrosion resistance, good weldability and no loss of strength at
welded joints, better high temperature thermal resistance, easy welding at site owing to better
ductility and bendability.
TMT-HCR rebars find wide application in different spheres including coastal and marine
environments which are susceptible to corrosion, bridges, flyovers, dams, industrial structures,
high rise buildings and underground platforms.
IQIH sxq2exh2gyysyx
When steel is exposed to atmosphere, it is subjected to action of atmospheric agencies. The
humid air causes the rusting of steel (the formation of oxides on the surface of steel), also the
atmospheric conditions along with rain produces oxidation and corrosion. Consequently, the
physical and mechanical properties are affected. In due course of time cracks and discontinuities
may form in the oxide film, due to electro-chemical action on the metal surface, providing a
fresh source of atmospheric action resulting in further corrosion. Once rusting is initiated, it
gradually increases and corrodes iron. Rusts in the form of scales are peeled off from the
swelled surface of iron. It is serious problem as the surface becomes rough with rusted iron
projections. This may injure users. Also, the loss of steel sectional area may cause failure of
structural elements.
Of the various theories of corrosion, the acid theory is applicable to the corrosion of iron.
According to this theory rusting is caused by action of oxygen, carbon di-oxide and moisture
converting the iron into ferrous bicarbonate. Further, the ferrous bicarbonate on oxidation
changes to ferric bicarbonate and subsequently to hydrated ferric oxide.
Fe + O + 2CO^2 + H 2 O = Fe (HCO 3 ) 2
2Fe(HCO 3 ) 2 + H 2 O + O 2Fe(OH)CO 3 + 2CO 2 + 2H 2 O
Fe(OH)CO 3 + H 2 O Fe(OH) 3 + CO 2
To safeguard iron and steel from rusting and corrosion some of the prevalent methods are
enamelling; applying metal coatings – galvanizing, tin plating, electroplating; and applying
organic coatings – painting and coal tarring. Of these methods painting is the most common.
Enamelling consists in melting a flux on the surface of iron in muffle furnace and then coating
it with a second layer of more fusible glaze. Galvanising is the process of coating iron with a
thin film of zinc, whereas in tin plating a film of tin is coated. Painting consists in applying a