Building Materials, Third Edition

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Steel for reinforcing bars can be classified according to its use. The earliest steel used for
construction purposes was plain mild steel bars, designated as Fe- 250 and so. Even nowadays
it is as engineers friendly as before in the underdeveloped and developing countries. For
impacts and suddenly applied loads mild steel reinforcement may prove to be a better choice
since high yield steels are more brittle and may fail under such conditions.

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r 2  2  2 2@r‰ƒhAbars have lugs, ribs, or deformations on the surface
(Fig. 13.6), which inhibit longitudinal movement of the bar relative to the surrounding concrete.
Thus, the deformed surface ensures better bond between reinforcement and concrete. These
bars do not have a definite yield point. HYSD bars result in a considerable increase in yield,
tensile and bond strength when twisted hot or cold. Cold twisted deformed (CTD) bars are
most suitable for building purposes and are widely used in India. CTD bars with trademark
TOR are called TOR-steel. Tor-steel is high strength deformed bars with high yield and bond
strength. These bars result in almost 40% economy.

„E™—™— 2 — 2 @„w„Abars are extra high strength reinforcing bars, which
eliminate any form of cold twisting. In this process, the steel bars receive a short intensive
cooling as they pass through a water cooling system after the last rolling mill stand.
The reduction in temperature converts the surface layer of the steel bar into a hardened
structure. This phase of intensive cooling is further followed by cooling in atmosphere, so that
the temperature of core (which is still hot) and the temperature of the cooled surface is
equalized. Hence, the surface layer gets tempered by the heat form the core. The resulting
structure is a tempered martensite zone at the periphery and a fine grain ferrite pearlite
structure in the centre zone. Due to the improved properties of high strength combined with