vertical type formwork not supporting the weight of concrete shall not be
removed in less than 24 hours after concrete placement is completed.[ Form
removal before 24 hours will be allowed for simple floor slab, sidewalks,
and driveways provided the ambient temperature during this period has not
fallen below 10 degrees C 50 degrees F at any time since placement and
evidence from compressive tests on field-cured concrete control cylinders
[or maturity instrumentation ]indicate[s] that the concrete has attained a
compressive strength of at least [_____] MPa psi. Control cylinders shall
be prepared for each set of forms to be removed before 24 hours. The
stability of the concrete shall be evaluated by a structural engineer prior
to removal of the forms.]
3.2.2
Formwork Supporting Weight of Concrete
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NOTE: ACI 347R suggests that at least 70 percent of
the design strength should be achieved before
removal of formwork support from horizontal members,
unless otherwise approved by the Contracting
Officer. (ACI 347R, paragraph 3.7.2.1) When
specifications are being prepared, a structural
engineer should determine the actual minimum
percentage of design strength that should be
achieved for the specific conditions on each
structure.
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Formwork supporting weight of concrete and shoring shall not be removed
until structural members have acquired sufficient strength to safely
support their own weight and any construction or other superimposed loads
to which the supported concrete may be subjected. As a minimum, forms
shall be left in place until control concrete test cylinders [or maturity
instrumentation] indicate evidence the concrete has attained at least
[_____] percent of the compressive strength required for the structure in
accordance with the quality and location requirements of Section [[_____]]
[_____], paragraph [_____].
3.2.3
Tunnel Forms
Tunnel lining bulkhead forms shall not be removed in less than 12 hours and
tunnel lining forms in not less than 16 hours.
3.3
INSPECTION
Forms and embedded items shall be inspected in sufficient time prior to
each concrete placement by the Contractor in order to certify to the
Contracting Officer that they are ready to receive concrete. The results
of each inspection shall be reported in writing.
-- End of Section --
SECTION 03101A
Page 9
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