An experienced concrete materials engineer or
[_____] should be consulted before allowing the use
of the maturity concept instead of compressive
strength test on field cured cylinders.
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Forms shall not be removed without approval. The minimal time required for
concrete to reach a strength adequate for removal of formwork without
risking the safety of workers or the quality of the concrete depends on a
number of factors including, but not limited to, ambient temperature,
concrete lift heights, type and amount of concrete admixture, and type and
amount of cementitious material in the concrete. It is the responsibility
of the Contractor to consider all applicable factors and leave the forms in
place until it is safe to remove them. In any case forms shall not be
removed unless the [minimum time][, ][ or ][minimum compressive strength][,
][ or ][minimum time, minimum ambient temperature, and minimum compressive
strength] requirements below are met, except as otherwise directed or
specifically authorized. When conditions are such as to justify the
requirement, forms will be required to remain in place for a longer period.
All removal shall be accomplished in a manner which will prevent damage to
the concrete and ensure the complete safety of the structure. Where forms
support more than one element, the forms shall not be removed until the
form removal criteria are met by all supported elements. Form removal
shall be scheduled so that all necessary repairs can be performed as
specified in Section [[_____]] [_____], paragraph [_____]. Evidence that
concrete has gained sufficient strength to permit removal of forms shall be
determined by tests on control cylinders. All control cylinders shall be
stored in the structure or as near the structure as possible so they
receive the same curing conditions and protection methods as given those
portions of the structure they represent. Control cylinders shall be
removed from the molds at an age of no more than 24 hours. All control
cylinders shall be prepared and tested in accordance with ASTM C 31/C 31M
and ASTM C 39/C 39M at the expense of the Contractor by an independent
laboratory that complies with ASTM C 1077 and shall be tested within 4
hours after removal from the site.[ After obtaining approval, the
Contractor may use maturity instrumentation instead of control cylinders to
determine the compressive strength of the concrete. ASTM C 1074 procedures
shall be used for estimating concrete strength by means of the maturity
method. All expenses associated with instrumenting the concrete and
evaluating the strength using maturity relationships shall be the
responsibility of the Contractor.]
3.2.1
Formwork Not Supporting Weight of Concrete
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NOTES: If form removal is to be allowed before 24
hours, the concrete must have sufficient strength to
resist damage from the removal operation. A minimum
of 3.5 MPa (500 psi) is recommended.
If the bracketed sentences below are deleted from
the project specification, the corresponding
submittal requirements for the evaluation and
results of control cylinder tests [or maturity
instrumentation] should also be deleted from
paragraph SUBMITTALS.
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Formwork for walls, columns, sides of beams, gravity structures, and other
SECTION 03101A
Page 8
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