Construction Process of RC Column

A reinforced concrete column is a structural member of an RC frame building. It is a vertical member which transfers loads from slabs and beams to the foundation, and the foundation transfers these loads to the soil.

A whole building depends on its columns. Therefore, it is important to know the proper construction process. Good design alone is not enough. Wrong column location, displaced bars, insufficient cover, weak formwork, poor consolidation, and early form removal can reduce the capacity and durability of the completed column.

The main construction stages are:

1. Column layout
2. Reinforcement fixing
3. Formwork erection
4. Pre-pour inspection
5. Concrete placement and consolidation
6. Curing, form removal, and final inspection

1. Column Layout Work

Start with the latest approved structural and setting-out drawings. Establish the grid lines using a total station, theodolite, or another approved surveying method. Then mark the centerline and faces of every column.

Do not locate a column only by measuring from an unfinished wall or slab edge. Check it from at least two control lines and confirm the offset dimensions shown on the drawings.

Before reinforcement work continues, verify:

• Column identification and grid intersection
• Column cross-section and orientation
• Starter-bar location and projection
• Top-of-concrete and construction-joint level
• Any change in column size between floors

2. Column Reinforcement Work

After marking the column location, place the reinforcement exactly as shown in the structural drawings and bar bending schedule.

A note such as:

C1: 12 bars of 16 mm diameter; ties: 10 mm diameter at 150 mm center to center

means that column C1 has 12 longitudinal bars, each 16 mm in diameter, and 10 mm transverse ties at the stated spacing. However, the drawing may require closer tie spacing near joints, lap zones, or the ends of the clear column height. Read all general notes and column schedules before fixing the cage.

Reinforcement Checks

• Number, diameter, grade, and location of longitudinal bars
• Tie diameter, spacing, hook details, and tie arrangement
• Lap-splice or mechanical-coupler location and length
• Required concrete cover and approved spacers
• Clear distance between bars for concrete flow and vibrator access
• Column cage alignment, stability, and connection to starter bars
• Beam-column joint reinforcement and any embedded items

3. Column Formwork

Column forms must be strong enough to resist the fresh-concrete pressure and all construction loads without excessive movement or leakage. They also need enough bracing to keep the column plumb during placement and vibration.

Before closing the form:

1. Remove wire pieces, sawdust, loose concrete, and standing water from the base.
2. Apply the approved form-release agent in a thin uniform coat. Do not contaminate reinforcement or the construction joint.
3. Check the inside dimensions and concrete cover.
4. Install chamfers, blockouts, inserts, and sleeves shown on the drawings.
5. Provide a cleanout opening when required, especially for tall or congested forms.
6. Close, tie, brace, and seal the formwork.
7. Check plumbness in two directions and recheck it during the pour.

The column casting height is determined from the actual levels on the drawings. For example, a 3.00 m floor-to-floor height minus a 0.45 m downstand beam depth gives 2.55 m to the beam soffit, not 2.65 m.

4. Pre-Pour Inspection Checklist

• Latest approved drawings available
• Grid location and orientation checked
• Column dimensions checked
• Longitudinal bars checked
• Ties and hooks checked
• Laps or couplers checked
• Cover blocks secured
• Embeds and sleeves secured
• Base cleaned
• Construction joint prepared
• Form joints sealed
• Forms braced and plumb
• Concrete access confirmed
• Vibrator and backup available
• Concrete testing arranged
• Pour sequence and crew briefed

5. Pouring Concrete Into the Column

Ready-mixed or properly controlled site-batched concrete can be used when it meets the approved mixture and project specification. The choice should be based on quality control, required volume, access, placing rate, and the available equipment. Site mixing is not automatically better than ready-mixed concrete.

1. Check the delivery ticket, mixture designation, batch time, and any project acceptance requirements.
2. Carry out the specified fresh-concrete tests and make strength specimens as required.
3. Place concrete as close as possible to its final position using a pump hose, elephant trunk, tremie, chute, or other suitable method.
4. Control free fall and placing rate so the concrete does not segregate and the form pressure stays within the formwork design.
5. Place the concrete in manageable lifts and consolidate each lift with the selected method.
6. Insert the internal vibrator vertically at regular spacing. Penetrate slightly into the previous lift, then withdraw slowly.
7. Do not use the vibrator to drag concrete sideways through congested reinforcement.
8. Watch for grout leakage, form movement, cage displacement, and loss of plumbness while pouring.
9. Complete the planned column lift continuously unless the drawings or method statement show an approved construction joint.

6. Consolidation Without Honeycombing

Consolidation removes entrapped air and helps the concrete flow around the bars and into the form corners. The method must match the workability, reinforcement congestion, and form geometry.

Too little vibration leaves honeycombs and voids. Too much vibration, poor insertion spacing, or using the vibrator to move concrete can cause segregation. When a joint is highly congested, solve the access and mixture problem before the pour rather than hoping extra vibration will fix it.

7. Curing and Form Removal

After placement, protect the top surface and start curing as soon as the surface condition permits. After the side forms are removed, continue the curing method required by the project. Suitable methods may include wet coverings, water application, plastic sheeting, or an approved curing compound.

Do not remove formwork only because a fixed number of hours has passed. Removal must follow the project requirements, the formwork plan, and confirmation that the concrete has enough strength for the loads and construction operations that will follow.

8. Inspection After Removing the Forms

• Check column dimensions, location, and plumbness.
• Inspect for honeycombing, exposed bars, voids, cold joints, fins, and surface cracking.
• Check the top level and the beam-column joint area.
• Record defects before patching.
• Do not cover a structural defect with mortar. Obtain an approved repair procedure and engineer review when required.

Common RC Column Defects and Causes

References and Related Articles

• ACI 347R, Guide to Formwork for Concrete.
• ACI 309R, Guide for Consolidation of Concrete.
• OSHA 1926.703, Requirements for Cast-in-Place Concrete.
• Basic Types of Stirrups for Concrete Work.
• Concrete in Compression.