403A Concrete Formwork 3 — Questions and Answers
Question 1: What is a kicker (or brace) in wall formwork and where is it positioned?
- A diagonal brace from the top of the form to an anchor on the ground to prevent the form from tipping (Correct answer)
- A wedge driven under the form to level it
- A horizontal member at the base of the form to seal the bottom
- A vertical post inside the form to support walers
Correct answer: A diagonal brace from the top of the form to an anchor on the ground to prevent the form from tipping
Kickers are diagonal braces running from the upper portion of the form down to ground anchors or floor anchors. They prevent the form from tipping outward under the lateral pressure and weight of the concrete and prevent overturn.
Question 2: What is the purpose of a grout stop (or base seal) at the bottom of a wall form?
- To prevent cement paste from leaking out at the form base during the pour (Correct answer)
- To anchor the form to the footing against uplift
- To provide a construction joint between the footing and wall
- To level the form base on uneven footings
Correct answer: To prevent cement paste from leaking out at the form base during the pour
Fresh concrete is fluid and cement paste can leak out through gaps at the base of the form. A grout stop (foam strip, rubber seal, or mortar) seals the bottom to prevent leakage, which would create voids, honeycombing, and grout loss at the bottom of the wall.
Question 3: What is 'honeycombing' in concrete and what causes it?
- Voids in the concrete surface caused by inadequate consolidation or cement paste leakage (Correct answer)
- A decorative exposed aggregate finish on concrete
- Cracking caused by thermal shrinkage
- Surface scaling caused by freeze-thaw cycles
Correct answer: Voids in the concrete surface caused by inadequate consolidation or cement paste leakage
Honeycombing appears as rough, porous, void-filled areas on the concrete surface after form stripping. It is caused by inadequate vibration (air and voids not consolidated), concrete mix that is too stiff, reinforcing steel that blocks flow, or leakage of cement paste through form joints.
Question 4: What is the difference between a control joint and an expansion joint in a concrete slab?
- Control joints are tooled or sawn to induce cracking at planned locations; expansion joints allow thermal movement between separate concrete sections (Correct answer)
- Control joints are filled with sealant; expansion joints are left open
- Control joints go through the full depth; expansion joints are only 25 mm deep
- There is no difference — both terms describe the same joint
Correct answer: Control joints are tooled or sawn to induce cracking at planned locations; expansion joints allow thermal movement between separate concrete sections
Control joints (contraction joints) are weakened planes that cause the concrete to crack at a predetermined location rather than randomly — they do not allow movement. Expansion joints use a compressible filler to allow adjacent slabs to move toward each other without cracking.
Question 5: What is the maximum allowable slump for structural concrete placed in wall forms under normal conditions per CSA A23.1?
- 100 mm (Correct answer)
- 200 mm
- 50 mm
- 150 mm
Correct answer: 100 mm
CSA A23.1 typically specifies slump limits of 80-100 mm for wall concrete without superplasticizers. Higher slump increases segregation and bleed water, reducing concrete quality. Actual slump limits depend on the mix design and project specifications.
Question 6: When building column forms, what is the purpose of a yoke (column clamp)?
- To resist the lateral pressure of concrete and hold the form panels tightly at correct dimensions (Correct answer)
- To lift the column form into position with a crane
- To align the column with plumb and prevent it from shifting
- To create the architectural reveals on the column face
Correct answer: To resist the lateral pressure of concrete and hold the form panels tightly at correct dimensions
Column yokes (or clamps) are external clamping devices placed around square or rectangular column forms at regular vertical intervals. They resist the outward bursting pressure of the fresh concrete, holding the form panels at the exact specified dimensions.
403A Concrete Formwork 3
What is a kicker (or brace) in wall formwork and where is it positioned?