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Concrete Formwork

Concrete Formwork. General Requirements Safe – must hold concrete in place until cured. Economical provide desired shape and surface texture Formwork usually cost more than the concrete. Typical formwork Can be wood Steel Aluminum

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Concrete Formwork

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  1. Concrete Formwork

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

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

  4. 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

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

  6. Construction Practices • Forms need tight joints • Forms need to be aligned and checked for alignment during pour • Don’t forget uplift on some types of forms • Don’t drop concrete more than 5’ • Don’t vibrate previously poured concrete too deeply – could cause form failure • Carefully remove forms – don’t want surface damage

  7. 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

  8. Formwork safety • Pg 321

  9. 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

  10. 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

  11. 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)

  12. 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

  13. Placing Reinforcing • Rebars kept in place by ties • F 11-30, 11-31

  14. 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

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