measured at least 20 minutes after mixing. Heating of the mixing water or
aggregates will not be permitted until the temperature of the concrete has
decreased to 7 degrees C 45 degrees F. The materials shall be heated in
such a manner that they will be free from ice, snow, and frozen lumps
before entering the mixer.]
3.3.2.5
Concrete Lifts
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NOTE: The required construction joints should be
shown in the drawings.
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The depth of concrete placed in each lift will be as shown in the drawings.
All concrete shall be deposited in approximately horizontal layers about
0.5 m 1-1/2 feet in thickness in stepped progression at such a rate that
the formation of cold joints will be prevented. Slabs shall be placed in
one lift, unless 0.8 m 2.5 foot or more deep. Where 2.3 m 7.5 foot or
greater lift depths are permitted, the Contractor shall furnish approved
cantilever forms that are jointed or hinged approximately midheight to
facilitate placement against surfaces sloping more than 10 degrees from
vertical. At the beginning of the placing of a lift, the top half of a
hinged or jointed form shall be retracted to such a position that it does
not interfere with the operation of buckets placing concrete adjacent to
the form. A minimum of five successive horizontal layers in stepped
progression shall be used for 2.3 m 7.5 foot lifts. Where 1.5 m 5 foot
lifts are required, a minimum of three successive horizontal layers in
stepped progression shall be used. Each new layer of concrete shall be
placed on the oldest exposed layer. The maximum exposed bulkhead face of
concrete between adjacent monoliths shall not exceed 12 m 40 feet except as
otherwise approved.
3.3.2.6
Immediately after placing, each layer of concrete shall be consolidated by
internal vibrating equipment. Vibrators shall not be used to cause
concrete to flow for significant distances within the forms. Hand spading
may be used if necessary together with internal vibration along formed
surfaces permanently exposed to view. Form vibrators shall not be used
unless forms are specifically designed for this use and unless specifically
approved. The vibrator shall be inserted vertically at uniform spacing
over the entire area of placement. The distance between insertions shall
be approximately 1.5 times the radius of action of the vibrator. The
vibrator shall penetrate rapidly to the bottom of the layer and at least
150 mm 6 inches into the preceding unhardened layer if such exists. It
shall be held stationary until the concrete is consolidated and then
withdrawn slowly. Slabs 200 mm 8 inches or less in depth shall be
consolidated by approved methods.
3.3.2.7
[Placing Concrete in Unformed Curved Sections
The unformed portion of the ogee crest, spillway bucket, and similar
features shall be finished by placing concrete slightly above grade,
consolidating and striking off to grade by accurate screeding. Screeding
may be accomplished by semimechanical devices or by a mechanical screed
that consolidates and screeds the surface in one operation. Ribs embedded
in the fresh concrete as guides for screeds will not be permitted.]
SECTION 03700
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