A Guide on How to Construct a Reinforced Concrete Column

aguideonhowtoconstructconcretecolumnThe reinforced concrete column is an important type of concrete element in a concrete building, especially a high-rise structure. It is highly recommended that in a building project, the design of concrete columns should be prioritized before the design of other concrete elements.

Perhaps you have noticed that there have been some concrete buildings which collapsed during their construction, and this may have happened because of design failure or lack of proper supervision. There are many possible reasons why reinforced concrete structures collapse during their construction. Therefore, it is vital to check every detail of a column before it is cast with concrete. Extra care should be taken during the inception of reinforced concrete column construction.

It is advisable to employ qualified construction staff such as a site structural engineer, a technical engineer, a construction manager, a project engineer and site engineer as these are the first experts on hand to check the soundness of the building design and eventually its on site application, in order to ensure the integrity of a completed (finished product) concrete element.

Qualified site crews are also required to do several critical tasks on site, especially concrete columns. The foreman, chargehand and steel fixers should have gained enough experience before they can be authorized and chosen to do the job of constructing vertical reinforcements, as it requires a highly knowledgeable team to interpret every detail of the structural plan.

So, to obtain a high-quality reinforced concrete column, here are 17 steps to follow for the construction of the concrete column.

1. Check the structural plan and install the reinforcing bars. Ensure that the proper bar diameter, grades of steel, and spacing are all inclined as per plan.

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2. Check which other trades like the electrical, sanitary, plumbing and mechanical trades are to be embedded along the column. If applicable, have them installed before the installation of formworks. Make sure that the openings of other trades are completely protected and closed from the wet concrete during the actual pouring.

3. Check the plan and install the formworks, properly braced, and tightened with the approved accessories and scaffolds. If necessary, a professional like a formworks engineers should certify that the formworks installed are credible enough to carry the load brought by the wet concrete and the pressure of the concrete pump (if pump is to be used).

4. Ensure that the plumb line is in-place on two adjacent sides. As a quality engineer or consultant, you have to check using steel tape if the plumb line is parallel to the column as it will show verticality.

5. Check the coordinates. Have the survey team check the placement of installed column formworks with respect to the gridlines to avoid deviations. Double check if necessary.

6. Ensure that the installed formwork is clean and free from laitance. Recheck if all the dowels, electrical, sanitary and plumbing provisions have been installed alongside with the formworks to avoid chipping work and rectification later on.

7. Prepare or batch the concrete. Concrete may be ready-mix concrete or in-situ mix. Recheck the designed strength needed and required for the structure. Should the concrete be in situ mix, make sure that the cement and aggregate mixtures is premium so as to get the designed strength.

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8. Collect samples for maturity testing. Normally, eight cube or cylinder samples are taken for a 7 day and a 28 day compression test, including spares. Check whether slump and temperature are in line with what was designed. Concrete should not be to “freshen up” with water or needed to be re-tampered in any way. Approved admixtures may be added as per specifications.

9. The inner surfaces of the formwork should be thoroughly wet, and free from laitance and deleterious substance before pouring fresh concrete.

10. For the actual casting, introduce the concrete continuously. A quality inspector must ensure that the concrete is cast as smoothly as possible and avoids the considerable height difference that promotes aggregate segregation. It is advisable to use steel chutes or plywood portable chutes whenever necessary. A quality inspector shall make sure that no concrete is used that has already hardened or does not meet the required quality control limits.

11. Concrete pumps must be lubricated using grout before starting the work. Grout shall be of 1 to 2 cubic meters of quantity.

12. Concrete mix shall be discharged within 1 and 1/2 hours after the water has been added to the dry mix, or after the concrete has been batched in the concrete batching plant.

13. If the weather will not permit the ongoing concreting works, a proper construction joint should be set up as per specs, and at the location where the stress is minimal. Check the structural plan and specs for reference.

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14. Whenever you can, avoid cold joint parts by putting the concrete in layer by layer, while the concrete continues to be in plastic form.

15. Take away the temporary spreader (if used) in the formworks when the concrete placing has already reached the elevation of the spreader.

16. The concrete should be compacted using a mechanical vibrator. The use of vibrators should be {limited to the time essential for consolidation. Avoid vibrating reinforcement and steel reinforcement for no reason should they be permitted to cause aggregate segregation. Provide a spare vibrator in case the one breaks down, to ensure the concrete pouring can continue.

17. Strictly speaking, concrete should be cast 1 and 1/2 hours after leaving the batching plant (for ready-mix concrete) and has a tolerance of up 2 hours. For an in situ mix, place the concrete as soon as possible.

After the concrete has settled and has attained its allowable strength on the specified day the safe stripping or removal of formworks may commence. Should there be any defect or noticeable bulges or honeycomb after the removal of formworks, it should be rectified by means of chipping, grinding or any approved tools. Burlap clothes or any approved similar materials are to be used for the reinforced concrete column curing. This is to ensure that the column will attain its designed strength at the right time.

Do you inspect column reinforcements before pouring concrete?  What can you suggest to avoid out of plumb concrete column after casting?

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