########### Structural Concrete

A.  **Forms and Reinforcement:**

    1.  Forms shall be sufficiently tight to prevent the leakage of
        mortar (check forms for noticeable \"openings\"). Metal ties and
        anchorages shall be constructed such that the embedded portion
        can be removed to a depth of at least 50mm (2 inches) from the
        concrete surface. Spec ref.

    2.  The form interior shall be cleaned of all chips, dirt, sawdust
        and other extraneous material before placement. Spec ref.

    3.  Corrugated metal form supports, when used for structural deck
        slabs, shall not be welded to the girder flanges in tension
        zones (also, metal forms shall not rest directly on the flange).
        Screed and runway supports shall not be located on the form
        sheets, form supports or reinforcing steel. Spec ref.

    4.  All chairs, tie wires and other devices shall be made of or
        coated with a dielectric material. For uncoated reinforcing
        steel, stainless steel chairs meeting ASTM A493 (AISI Type 430)
        requirements without polyethylene tips may also be used. Spec
        ref.

    5.  Prior to installation all grease, dirt and other foreign
        substances shall be removed from the reinforcing steel. Damaged
        reinforcing steel coating (6mm x 6mm area or greater) shall be
        repaired with a material supplied by the coating applicator.
        Spec ref.

    6.  Reinforcing steel supports shall be placed no further than 1.2
        meters (4 ft) apart and no closer than 150 mm (0.5 ft) from the
        edge of a concrete surface. Spec ref.

    7.  Bar reinforcement placement tolerances are +/- 6mm (0.25 inches)
        vertical and +/- 13mm (0.50 inches) horizontal from the plan
        spacing (see deck cross section and reinforcing layout plan
        sheets for details). Top and bottom mats shall be tied together
        1.2 meters (4 ft) on centers. Spec ref.

B.  **Material Quality Assurance** (Spec References):

    1.  Transit mixed concrete will be delivered to the site with a
        minimum 100 mixing revolutions. There can be two additions of
        water, with 30 mixing revolutions each, to achieve initial slump
        for the class of concrete. Class DP and HP Concrete can have a
        total of 100 to 200 mixing revolutions while all other classes
        can have 100 to 160 mixing revolutions (concrete properties are
        outlined in (Spec ref., Table XXX, \"Concrete Mixtures\").

    2.  For mixes containing water-reducer and set-retarding admixtures,
        the time from material batching to full discharge shall not
        exceed 90 minutes (typically structural decks). For mixes
        without these admixtures, the 90 minutes maximum applies to the
        batch to placement of subsequent lifts or strike off time frame
        (usually substructure elements).

    3.  Concrete having a discharge temperature exceeding 32C (90 F)
        will be subject to rejection. The concrete shall also have a
        slump and air content within the ranges specified for the
        concrete class and mix design (Table 501-3 is attached showing
        the ranges). The slump and air content tests will be performed
        initially and every 40 cubic meters (50 cubic yards) thereafter.

    4.  A set of concrete cylinders will be made for each structural
        component initially and every 150 cubic meters (200 cubic yards)
        thereafter. Twenty-eight day cylinder breaks should be reviewed
        to assure the compressive strength for the mix design has been
        met.

C.  **Concrete Placement:**

    1.  Screed rail supports shall be placed 600mm (2 ft) on centers.
        Finishing machines are subject to approval by the RCE and are
        usually the power driven one-operation (strike-off auger,
        finisher roller) type. All one-operation machines shall also
        have a pan float. Spec ref.

    2.  Before concrete operations are started, the concrete machine
        shall be operated over the full length of the bridge segment to
        be constructed (\"dry-run\"). The screed shall be set to its
        finishing position for this test and the screed rails adjusted
        as needed and reinforcing \'cover\' checked. Spec ref.

    3.  [Existing concrete surfaces]{.underline} shall be free of loose
        or foreign material, scrubbed with wire brooms and kept wet
        before new concrete is placed. Immediately before placement, the
        [old surface]{.underline} shall be thinly coated with a 1:1
        portland cement mortar. Spec ref.

    4.  Concrete shall not be placed if the ambient air temperature is
        below 7C (45F) and/or the temperature will fall below 0C (32F)
        during the curing period unless the Engineer gives approval per
        the Cold Weather Concreting Provisions (In this case, use Cold
        Weather Concreting IID for this review).

    5.  Structural slab and sidewalk placements shall not proceed if the
        evaporation rate is theoretically equal to, or greater than, 1.2
        kg/sq. meter/hour. The evaporation rate shall be verified by the
        prime contractor. The test equipment shall be properly
        calibrated. The engineer can request re-tests as weather
        conditions change. Spec ref.

    6.  When concrete pumps are used, the lines shall have a minimum
        diameter of 125mm (5 inches). Chutes, troughs and pipes shall be
        kept clean and free of hardened concrete. Concrete material
        shall not be dropped a distance of 1.5 meters (5 ft) nor
        deposited in large quantities at any one point. Spec ref.

    7.  Concrete vibrators shall have a frequency of 3500
        impulses-per-minute. For structural decks, one vibrator is
        required for every 30 cubic meters (39 cubic yards) placed per
        hour, with a minimum of two vibrators in use at all times. One
        additional vibrator shall be available as backup. Spec ref.

    8.  The vibrators shall be inserted into the plastic concrete in as
        near a vertical position as possible. The vibration time shall
        be sufficient to consolidate the concrete around reinforcement
        and at the form corners / edges. Vibrators shall not be used to
        push or distribute the concrete laterally. Over-vibrating, which
        creates pools of grout, shall be avoided. Spec ref.

    9.  If there was a bridge deck pour sequence specified in the plans,
        the reviewer should verify whether this sequence was followed.

D.  **Concrete Finishing:**

    1.  As the concrete placement proceeds, the engineer shall verify at
        random the \"cover\" between top-of-slab and top-of-upper-mat
        \[tolerances are +/- 13mm (0.5 inches)\]. Spec ref.

    2.  Initial texturing will be done via an artificial turf drag. The
        turf type and brand shall appear on the State\'s \"Approved
        List\". The drag shall be cleaned periodically to remove
        hardened particles. Texturing shall stop 300mm (1 ft) from curbs
        or barriers. Spec ref.

    3.  Finished plastic concrete deck surfaces have a +/-6mm (0.25
        inch) tolerance when compared to the plan elevation. Before
        texturing, the deck will be checked with a minimum 3-meter (10
        ft) length straightedge. Irregularities greater than 5mm in 3
        meters shall be corrected. Spec ref.

E.  **Curing Requirements** (Spec ref.):

    1.  Five minutes after texturing (30 minutes after concrete
        placement), the deck surface shall be covered with wet burlap.
        Lapping shall be at least 300mm (1 ft). The burlap shall be
        continuously wet beginning ten minutes after placing and be
        protected from displacement.

    2.  Substructure elements shall be covered and cured for seven days
        using curing covers, wet burlap or both. Clear (fugitive dye)
        curing membrane can also be used for everything except
        structural slabs. Note: Curing covers are either Plastic Coated
        Fiber Blankets or Polyethylene (white opaque) Curing Covers.

    3.  Superstructure slabs shall be cured by either 14-days continuous
        burlap wetting or 7-days continuous burlap wetting, followed up
        with covering with curing covers.

    4.  Curing covers shall be lapped a minimum of 300mm (1 ft) and the
        lapped edges sealed with pressure sensitive tape. The covers
        shall be protected against displacement.

    5.  Structural approach slabs, curbs, sidewalks and safety walks on
        bridges shall be cured for 7-days by continuous wetting of the
        wet burlap. Forms may be stripped from approach slabs before the
        seven days have passed. However, curing must proceed using one
        of the methods discussed under E2 above.

    6.  Approach slabs and sidewalks and safety walks on bridges can be
        subjected to full legal loads after the 7-day curing period.
        Superstructure slabs can receive the full legal load after
        28-days. However, full loading is allowed after the 14-day wet
        curing period provided the average compressive strength of two
        concrete cylinders breaks is 21 Megapascals (3000 psi) and no
        individual cylinder break is less than 19.5 Megapascals (2800
        psi).

    7.  Typically, form stripping will not occur on superstructure
        elements until the curing periods described previously have
        ended. Regarding substructure elements.

F.  **Other Requirements:**

    1.  For superstructure slabs having corrugated metal forms, a
        section of form shall be removed (after two curing days, and
        prior to the next placement) from the most recently completed
        placement of each span to check for soundness. After ten days
        but prior to the next placement, the engineer will hammer
        \"sound\" 50% percent of the area of 25% percent of the form
        panels. Panel removal and sounding can be moderated after a
        substantial amount of the deck has been placed and the results
        have been satisfactory. Spec ref.