The reinforced concrete column is a pillar that stands as the carrying channel for the structure above it. Thus, expect for immense compression stress this member comes across. Highly compressed plus the shear stress due to live load and wind load a building encounters, this member has to be planned thoroughly before casting.
Proper protocol is followed to attain the design strength of the concrete columns. Generally, quality assurance and control engineer checks the spacing, bar diameters, splicing, dowel provisions if it followed the specifications and plan.
Furthermore, as columns are vertical structure, formwork engineers should strictly check the credibility of formworks and support before the pouring. So with the shoring and anchorages if it can carry the pressure and load of the wet concrete. Once approved, concreting engineer then prepares the manpower and the equipment to be used for the actual casting.
The casting procedure is as follows.
1. Collect samples for maturity testing. Check slump and temperature if inclined with what’s designed. Concrete should not be “freshen up” with water or re-tampered in any way.
2. The surfaces of construction joints should the thoroughly wet, free from laitance before pouring fresh concrete.
3. For the casting, deposit concrete continuously. Make sure that concrete is cast as neatly as possible and avoid considerable height difference that promotes aggregates segregation. Use chutes if necessary. Make sure that no concrete that has already settled or “unworkable” is used, or does not meet the required quality control limits.
4. Concrete pumps (lubricated using mortar before starting the work) may be used if necessary.
5. Concrete mix should be used and cast within one and one-half hour (1 1/2) after water has been added to the dry mix.
6. Should the weather does not permit the ongoing concreting works; proper construction joints should be established as per specifications and at the location where the stress is minimum.
7. As much as possible, avoid cold joints by placing layer by layer while the concrete is still in plastic form.
8. Remove the temporary spreader (if used) in the formworks when the concrete placing has reached the elevation of such spreader.
9. The concrete should be compacted using a mechanical vibrator. The use of vibrators should be limited to the time necessary for consolidation. By any means, do not vibrate forms or reinforcement. Under no circumstances should they be allowed to cause aggregate segregation. Prepare for spare vibrator should the other one malfunction.
10. Strictly speaking, concrete should be cast max 0f 2 hours after leaving the batching plant (for ready-mix concrete).
After the concrete has settled and has attained its designed strength safe for stripping, removal of formworks may commence. Should there be any defect or noticeable bulges after the removal of formworks, it should be rectified by the means of chipping, grinding or any approved tools.
Burlap clothes or any approved equal materials are to be used for the column curing. This is to ensure that the column will attain its designed strength at the right time.
Hi, if I have 5 m concrete column in length and I cast the first meter and after 30 minutes I cast 2 m and after 30 minutes I cast the last 2 m is there any risk or any mistake in this procedure?
Yes. The concrete setting time is almost achieved at that time. You will have most probably cold joint then. I prefer to always plan your castings so that you will not arrive in this similar case.