CSLB General Building (B)Site Work, Foundations and ConcreteMedium
A concrete finisher is placing rebar in a slab-on-grade and uses plastic rebar chairs before the pour. What is the primary purpose of these chairs?
- ATo hold the rebar at the correct height, ensuring proper concrete cover
- BTo prevent the rebar from corroding during transport and storage
- CTo increase the tensile strength of the reinforcing steel
- DTo create expansion joints at regular intervals in the slab
Show answer & explanationAnswer & explanation
Correct answer: A. To hold the rebar at the correct height, ensuring proper concrete cover
Rebar chairs suspend reinforcing steel at the specified height within the formwork so that the required concrete cover is achieved on all sides once the concrete is poured. Without chairs, rebar can settle onto the subgrade, resulting in inadequate cover and corrosion risk.
Why the other options are wrong
- B. Corrosion prevention is unrelated to the chair's structural function during placement.
- C. Chairs do not alter the steel's material properties or strength.
- D. Expansion joints are a separate slab feature unrelated to rebar chairs.
Rebar Chairs (Spacers)
Small supports made of plastic, metal, or concrete used to hold reinforcing steel at a specified height and position within formwork prior to concrete placement.
- Ensure correct concrete cover for corrosion protection and structural performance
- Prevent rebar from resting directly on subgrade or form face
- Available in various heights matched to design cover requirements
Memory trick: Chairs lift the bars so cover isn't scarce.