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Reinforced Concrete Multi Story Construction 2

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CivilSigma

CivilSigma

Structural
Nov 16, 2016
100
I understand that cold joints can form at the interface between two batches of concrete that are allowed to cure at different times. I also understand that as structural engineers we do not like cold joints as they alter intended design behavior (from moment to pin behaviour).

In multi-story reinforced concrete construction, you do not obviously cast your columns in one shot. I often times see rebar from already cured (half?) portions of concrete columns. So my question is, when the contractor goes to build the story above, how do they mitigate cold joints at the interface of the top of the cast column and new concrete that will be poured?

Thank you.
 
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Cleanout thoroughly, apply grout or bonding agent.
 
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CivilSigma said:
they alter intended design behavior (from moment to pin behaviour)
Click to expand...
If detailed properly you can maintain moment transfer across a cold joint.
Review the Shear-Friction provisions and check out ACI 224.3R-95.

My Personal Open Source Structural Applications:

Open Source Structural GitHub Group:
 
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Is it common practice to use grout or bonding agent when adding a new column lift? I have never seen it done. The new column lift is normally poured on a floor slab, often with lower strength than that of the column. A higher strength concrete could be used in the slab at each column location, but that is usually not necessary because confinement is much better in the slab than the column, justifying a lower strength. Also, mixing concrete strengths in a floor slab is a recipe for disaster.



BA
 
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Nor I... They generally clean the top of the columns to make sure there is no laitance or debris (or snow or ice depending on where you are) and simply pour the slab over making sure the column does not project into the slab. the column above is then cast onto the slab. Sometimes with high strength concrete columns you have to look at the column-slab interface.

Dik
 
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Grout here is just cement mortar, I call it all the time for high lift with cold joint in between lifts.
 
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Perhaps it is regional terminology, but a cold joint to me implies that it happens during the same pour and is not intentional - previously placed concrete has become semi plastic and has fresh concrete placed against it due to some delay in the placement sequence. The situation described by the OP is a construction joint, which are planned and detailed for.
 
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Dauwerda is correct. Examples of poorly prepared joints.

j_owcpj1.png
 
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