STEEL REINFORCEMENT
Steel reinforcement bars, if supplied or arranged
by contractor, shall be either plain round mild steel bars grade as per IS 432
(part-I) or medium tensile steel bars as per IS 452 (part-I) or hot rolled mild
steel ad medium tensile steel deformed bars as per IS 1139 or cold twisted
steel bars and hot weld strength deformed bars as per IS 1786, as shown and
specified on the drawings. Wire mesh or fabric shall be in accordance with IS
1566. Substitution of reinforcement will not be permitted except upon written
approval from Engineer-in-charge. Storage :
The reinforcement steel shall not be kept in
direct contact with ground but stacked on top of an arrangement of timber
sleepers or the like. Reinforcement steel shall be with cement wash before
stacking to prevent scale and rust. Fabricated reinforcement shall be carefully
stock to prevent damage, distortion, corrosion ad deteriorations.
Quality :
All steel shall be grade I quality unless specifically
permitted by the Engineer-in-charge. No rolled material will e accepted. If
demanded by the Engineer-in-charge. Contractor shall submit the manufacturers
test certificate for steel. Random tests on steel supplied by contractor may be
performed by Department as per relevant Indian Standards. All costs incidental
to such tests shall be at contractors expense. Steel not conforming to specifications
shall be rejected. All reinforcement shall be clean, free from grease, oil,
paint, dirt loose mill, scale dust, bituminous materials or any other
substances that will destroy or reduce the bond. All rods shall be thoroughly
cleaned before being fabricated. Pitted and defective rods shall not be used.
All bars shall be rigidly held in position before concreting. No welding of
rods to obtain continuity shall be allowed unless approved by the Engineer-in-
charge. If welding is approved, the work shall be carried as per 2751,
according to best modern practices ad as directed by the Engineer-in-charge in
all cases of important connections, tests shall be made to prove that the
joints are of the full strength of bars welded. Special specifications, as
specified by the Engineer-in-charge, shall be adhered to in the welding of cold
worked reinforcing bars and bars other than mild steel.
Laps :
Laps ad splices for reinforcement shall be shown
in the drawings. Splices, in adjacent bars shall be staggered ad the locations
of all splices, except those pecified on the drawing shall be approved by the
Engineer-in-charge. The bars shall not be lapped unless the length required
exceeds the maximum available length of bars at site.
Bending :
All bars shall be accurately bent according to the
sizes ad shapes shown on the detailed working drawings/ bar being schedules.
They shall be bent gradually by machine or other approved means. Reinforcing
bars shall not be straightened and rebent in a manner that will injure the
materials. Bars containing cracks or splits shall be rejected. They shall be
bent cold, except bars of over 25mm in diameter which may be bent hot if
specifically approved by the Engineer-incharge. Bars bent hot shall not be
heated beyond cherry red colour (not exceeding 645oC ) and after bending shall
be allowed to cool slowly without quenching. Bars incorrectly bent shall be
used only of ht means used for straightening and rebinding be such as shall
not, in the opinion of the Engineer-in-charge injure the material. NO
reinforcement bar shall be bent when in position in the work without approval,
whether or not it is partially embedded in ardened concrete. Bars having links
or bends other than those required by
design
shall not be used.
Bending
at Construction Joints :
Where reinforcement
bars are bent
aide at construction
joints and afterwards
bent
back into their original position, care should be taken to
ensure that no time the radius of the bend is less than 4 bar diameters for
plain mild steel or 6 bar diameters for deformed bars. Care shall also be taken
when bending back bars to ensure that the concrete around the bar is not
damaged.
Fixing /
Placing ad Tolerance on Placing :
Reinforcement shall be accurately fixed by ay
approved means maintain din the correct position as shown in the drawings by
the use of blocks, spacer and chairs as per IS 2502 to prevent displacement
during placing ad compaction of concrete. Bar intended to be in contact at
crossing point shall be securely bound together at all such points with number
16 gauge annealed soft iron wire. The vertical distances required between
successive layers of bars in beams or similar members shall be maintained by
the provision of mild steel spacer bars at such intervals that the main bars do
not perceptibly sag between adjacent spacer bars.
Tolerance
on placing of reinforcement :
Unless otherwise specified by the
Engineer-in-charge, reinforcement shall be placed within the following tolerances:
Tolerance
in spacing
a) For
effective depth, 200 mm or less + 10 mm
b) For
effective depth, more than 200 mm + 15 mm
Cover to
Reinforcement :
The cover
shall in no case be reduced by more than one third of specified cover or
5mm whichever is less. Unless indicated otherwise on the
drawings, clear concrete cover for reinforcement (exclusive of plaster or other
decorative finish shall be as follows) :
a) At each end of reinforcing bar not less than 25
mm, nor less than twice the diameter of such bar.
b) For a
longitudinal reinforcing bar not less than 25 mm, nor more than 40 mm, nor less
than the diameter of such bar. In the case of
column of maximum dimensions of 200mm or under, whose reinforcing bars do not
exceed 12mm, a cover of 25mm may be used.
c) For
longitudinal reinforcing bar in a bar, not less than 25 mm nor less than the
diameter of such bar and.
d) For
tensile, compressive, shear, or other reinforcement in a slab, not less than
25mm,
nor less
than the diameter of such bar and.
e) For any
other reinforcement not less than 15mm, nor less than the diameter of such bar.
f) Increased cover thickness may be provided when
surfaces of concrete members are exposed to the action of harmful chemicals (as
in the case of concrete in contact with earth faces contaminated with such
chemicals), acid, vapour, saline, railways) etc. and such
increase of cover may be between 15mm and 50 mm beyond the
figures given in (a to e) above as may be specified by the Engineer-in-charge.
g) For
reinforced concrete members, totally immersed in sea water the cover shall be
40mm, more than specified ( a to e) above.
h) For
reinforced concrete members, periodically immersed in sea water or subject to
sea spray, the cover of concrete shall be 50 mm more than that specified (a to
e) above.
i) For concrete of grade M25 and above, the additional
thickness of cover specified in (f),
(g) and (h) above a my be reduced to half. In all such cases
the cover should not exceed 75mm.
j)
Protection to reinforcement in case of concrete exposed to harmful surroundings
may
also be given by providing a dense impermeable concrete with
approved protective coating as specified on the drawings. In such case, the
extra cover, mentioned in (h) and (i) above, may be reduced by the
Engineer-in-charge, to those shown on the drawing.
k) The correct cover shall be maintained by cement mortar
briquettes or other approved means. Reinforcement for footings, grade beams ad
slabs on sub grade shall be supported on precise concrete blocks as approved by
the Engineer-in-charge. The use of pebbles or stones shall be permitted.
l) The minimum clear distance between reinforcing
bars shall be in accordance with IS 456 or as shown in drawings.
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