Building Design and Construction Handbook - Merritt - Ventech!

CONCRETE CONSTRUCTION 9.33
as well as recommended maximum spacings and details for use, are given in the
CRSI ‘‘Manual for Standard Practice.’’
Wire bar supports are generally available in the United States in three classes
of rust prevention: plastic-protected, stainless-steel-protected, and no protection
(plain). Precast-concrete bar supports are normally supplied in three styles; plain
block, block with embedded wires, and block with a hole for the leg of a vertical
bar for top- and bottom-bar support.
Various types and sizes of all-plastic bar supports and sideform spacers are
available. Consideration should be given to the effects of thermal changes, inasmuch
as the coefficient of thermal expansion of the plastic can differ significantly from
that of concrete. Investigation of this property is advisable before use of all-plastic
supports in concrete that will be exposed to high variations in temperature.
Bar supports for use with epoxy-coated rebars should be made of dielectric
material. Alternatively, wire bar supports should be coated with dielectric material,
such as plastic or epoxy.
9.27 INSPECTION OF REINFORCEMENT
This involves approval of rebar material for conformance to the physical properties
required, such as ASTM specifications for the strength grade specified; approval of
the bar details and placing drawings; approval of fabrication to meet the approved
details within the prescribed tolerances; and approval of rebar placing.
Approvals of rebar material may be made on the basis of mill tests performed
by the manufacturer for each heat from which the bars used originated. If samples
are to be taken for independent strength tests, measurements of deformations, bending
tests, and minimum weight, the routine samples may be best secured at the mill
or the fabrication shop before fabrication. Occasionally, samples for check tests are
taken in the field; but in this case, provision should be made for extra lengths of
bars to be shipped and for schedules for the completion of such tests before the
material is required for placing. Sampling at the point of fabrication, before fabrication,
is recommended.
Inspection of fabrication and placement is usually most conveniently performed
in the field, where gross errors would require correction in any event.
Under the ACI 318 Building Code, the bars should be free of oil, paint, form
coatings, and mud when placed. Rust or mill scale sufficiently loose to damage the
bond is normally dislodged in handling.
If heavily rusted bars (which may result from improper storage for a long time
exposed to rusting conditions) are discovered at the time of placing, a quick field
test of suitability requires only scales, a wire brush, and calipers. In this test, a
measured length of the bar is wire-brushed manually and weighed. If less than 94%
of the nominal weight remains, or if the height of the deformations is deficient, the
rust is deemed excessive. In either case, the material may then be rejected or penalized
as structurally inadequate. Where space permits placing additional bars to
make up the structural deficiency (in anchorage capacity or weight), as in walls
and slabs, this solution is preferred, because construction delay then is avoided.
Where project specifications impose requirements on rust more severe than the
structural requirements of the ACI 318 Building Code, for example, for decorative
surfaces exposed to weather, the inspection should employ the special criteria required.