Importance of Rebar Chairs during Concrete Pouring

During concrete works, one detail that often goes unnoticed by non-engineers is the rebar chair. These small supports hold reinforcement bars at the correct height before and during concrete pouring.

To many workers, rebar chairs seem insignificant, but to engineers, they are essential for ensuring structural strength, durability, and accurate reinforcement. Without proper chairs, reinforcement shifts during concreting, altering the designed cover, and weakening the structural element.

1. Rebar Chairs Maintain Correct Concrete Cover

Concrete cover is the protective layer of concrete over the reinforcement. It protects steel from corrosion, fire, and weathering. During pouring, reinforcement cages tend to sink or float if not supported. Chairs hold rebar at the exact height needed for:

1. Bottom cover
2. Top cover
3. Side cover

Without chairs, the cover becomes inconsistent. Even small reductions in cover expose reinforcement to moisture and air, eventually causing corrosion and spalling.

2. Chairs Prevent Rebar Movement During Pouring

Concrete pour involves vibration, heavy tools, and significant movement. Reinforcement shifts easily if not fixed firmly. Chairs:

1. Prevent sinking due to worker weight
2. Stop rebar lifting while placing concrete
3. Maintain spacing when vibrators touch the bars
4. Keep bar alignment stable despite flow pressure

Once the cage moves, it is impossible to correct it after the concrete has been placed. Chairs eliminate this risk.

3. Chairs Help Maintain Structural Depth

Structural depth is the distance between the top and bottom reinforcement layers. This depth determines:

1. Load-carrying capacity
2. Flexural strength
3. Crack control
4. Deflection limits

If bars sink during pouring, the effective depth reduces, weakening the slab or beam. Chairs keep both layers at the designed positions, preserving structural performance.

4. Chairs Improve Concrete Consolidation

Proper chair spacing ensures the reinforcement is elevated and concrete can flow around and under the bars. When bars sit directly on formwork without chairs:

1. Concrete cannot fill beneath reinforcement
2. Honeycombing occurs
3. Voids form at the bottom surface

Good consolidation around rebars enhances bonding, durability, and strength.

5. Chairs Ensure Accurate Spacing Between Rebars

Rebars require proper spacing for concrete flow and structural behaviour. Chairs (especially spacers and supports in beam cages) help maintain:

1. Clear spacing
2. Uniform load transfer
3. Proper anchorage and lap development

Incorrect spacing leads to congestion or wide gaps, both of which affect structural integrity.

6. Chairs Improve Quality Control on Site

Rebar chairs make it easy for engineers to verify reinforcement placement. Without them, it is difficult to confirm that bars are at the correct height or are properly aligned. Chairs provide:

1. A consistent support system
2. Clear visual confirmation
3. Better reinforcement layout tracking

This improves inspection outcomes and ensures the structure matches drawings and code requirements.

7. Chairs Reduce Long-Term Corrosion Risk

Incorrect concrete cover is the most common cause of reinforcement corrosion. When bars touch formwork directly, moisture, chemicals, and air can easily reach the steel. Chairs prevent steel from contacting:

1. Shuttering
2. Soil
3. Masonry
4. Plastic sheets

Proper cover achieved through chairs slows corrosion and extends the life of the structure

8. Chairs Support Worker Movement on Rebar Cage

During reinforcement tying and concreting, workers step on rebar mats. Without chairs, the cage flexes and sinks, disturbing alignment. Chairs:

• Transfer weight to the formwork
• Prevent displacement under foot pressure
• Provide a stable walking surface indirectly

They help keep reinforcement undisturbed during site activities.