Concrete Formwork General Requirements Safe must hold concrete

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 – Must be braced to withstand load (concrete weighs 150 pcf)

– 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

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

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

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

Formwork safety • Pg 321

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

Reinforcing Steel • Welded wire fabric – Common for slabs – Smooth or deformed wire – WWF is identifier – WWF 6 x 6 -4. 0 x 4. 0 is a welded wire fabric with 6 inch spacing longitudinally and transversely made of W 4 size (0. 04 x section area) wire

• 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)

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

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

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