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 150pcf)

– 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 1/8th 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 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

• 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