Concrete Formwork

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Concrete Formwork
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• General Requirements
• Safe must hold concrete in place until cured.
• Economical
• provide desired shape and surface texture
• Formwork usually cost more than the concrete

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• Typical formwork
• Can be
• wood
• Steel
• Aluminum
• Must be braced to withstand load (concrete weighs
  150pcf)

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• Wall form F 11-18
• Double wales used above and below ties to allow
  tie to be secured
• Also need a spreader to keep forms correct
  distance apart
• Need to have good bracing at foot of form
• Ties F 11-19
• Most common can be broken off just inside
  concrete allows for patching

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• Column Forms
• Use column clamps for support/bracing
• May have windows to making pouring easier
• F 11-20
• Slabs
• F 11- 21 -gt 11-25

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Construction Practices

• Forms need tight joints
• Forms need to be aligned and checked for
  alignment during pour
• Dont forget uplift on some types of forms
• Dont drop concrete more than 5
• Dont vibrate previously poured concrete too
  deeply could cause form failure
• Carefully remove forms dont want surface
  damage

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Expansion and control joints

• Permit differential movement in concrete shapes
• Concrete shrinkage, temperature change, moisture
  change, settlement
• Isolate interior columns from floor slab cut
  around column

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Formwork safety

• Pg 321

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Reinforcing Steel

• Reinforcing bars
• Usually deformed (manufactured with ridges to
  increase bond with concrete)
• Can be plain or epoxy coated
• Sized by 1/8th inch and strength of steel
• T 11-1, F 11-28

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Reinforcing Steel

• Welded wire fabric
• Common for slabs
• Smooth or deformed wire
• WWF is identifier
• WWF 6x6-4.0x4.0 is a welded wire fabric with 6
  inch spacing longitudinally and transversely made
  of W4 size (0.04 x section area) wire

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• Spirals (for columns)
• 3 standard sizes 3/8 inch, ½ inch, 5/8 inch
  diameter rods
• Sprial diameters (outside to outside) 12 minimum
  to 33 max
• Pitch from 1.75 3.25 (distance from center to
  center of rod)

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Placing Reinforcing

• Rebar goes in areas of tension
• F 11-29
• Need to protect rebar from corrosion fire and
  weather
• Pg 325 gives min cover
• Minimum clear distance between parallel bars in
  columns 1.5 or 1.5 x max aggregate size
• For other shapes 1 or 1.333 x max aggregate size

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Placing Reinforcing

• Rebars kept in place by ties
• F 11-30, 11-31

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QC

• Common deficiencies
• Pg 329
• Inspection and Testing
• Usually concrete is a fast paced activity
• Need to inspect product from stockpile to
  placement and then test for strength, air
  entrainment, beam flexure