placement. Tepid water is water at a temperature no
more than 7 degrees C (20 degrees F) cooler than the
surface of the concrete placement. For massive
placements, thermal insulation should be provided to
reduce the temperature gradient between the interior
and exterior of the placement.
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[Concrete containing silica fume shall be moist cured.] Horizontal and
nearly horizontal surfaces shall be moist cured by ponding, by covering
with a minimum uniform thickness of 50 mm 2 inches of continuously
saturated sand, or by covering with saturated nonstaining burlap or cotton
mats. Burlap and cotton mats shall be rinsed to remove soluble substances
before using. Other surfaces shall be moist cured when approved or
directed. Concrete that is moist cured shall be maintained continuously,
not periodically, wet for the duration of the entire curing period. Water
for curing shall comply with the requirements of the paragraph WATER. If
the water, sand, mats, etc. cause staining or discoloration of permanently
exposed concrete surfaces, the surfaces shall be cleaned by a method
approved. When wood forms are left in place during curing, the forms shall
be kept continuously wet except for sealed insulation curing in cold
weather. When steel forms are left in place on vertical surfaces during
curing of concrete, [when using high-strength concrete] [when concrete
being cured has a water-cement ratio less than 0.40] [placements with a
minimum dimension greater than 600 mm 2 feet] the forms shall be carefully
broken loose from the hardened concrete and curing water continuously
introduced into the void. The temperature of the water should be tepid.
Horizontal construction joints shall be allowed to dry sufficiently to
remove free water immediately prior to placing the next lift.
3.5.3
Membrane Curing
Membrane curing may be used on surfaces that are not specified or directed
to receive moist curing and that are not to receive a grout-cleaned finish.
Membrane-forming curing compound shall not be used on surfaces that
contain protruding steel reinforcing, that are heated by free steam, that
will have additional concrete bonded to them, or that are to be
grout-cleaned.
3.5.3.1
Pigmented Curing Compound
Pigmented compound conforming to ASTM C 309, Type 2, Class A, may be used
on surfaces that will not be exposed to view when the project is completed.
Only pigmented compound of the styrene acrylate or chlorinated rubber
formulation conforming to ASTM C 309, Class B, requirements may be used on
surfaces that are to be painted or to receive bituminous roofing or water
proofing or floors that are to receive adhesive applications of resilient
flooring. The curing compound selected by the Contractor for such use
shall be compatible with any subsequent paint, roofing, coating, or
flooring specified elsewhere in the contract.
3.5.3.2
Nonpigmented Curing Compound
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NOTE: See the concrete materials design memorandum
for guidance on the optional sentence.
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Nonpigmented compound conforming to ASTM C 309, Type ID, containing a
SECTION 03700
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