Cold joint vs Construction Joint 1

[WWTEng]

What time lapse between two concrete pours makes the joint in-between a cold joint? Consider 60-80 F temperature, normal weight 3000-4000 psi concrete with standard type 1 cement. The question for SOG as well concrete one metal deck (elevated slab).

I am guessing that ideally one should strive to prepare every cold joint as a construction joint. This way the next pour could be placed almost anytime.

 

[OHIOMatt]

The time frame is dependent upon too many factors to provide any real answer. These include, but are not limited to; relative humidity, exposure to the sun, exposure to wind, temperature of the raw materials, time in the truck, admixtures, aggregate type etc. We state that any placement be made in a continuous manner while the concrete is still in the fluid state. If an interuption in placement is required due to unforeseen conditions, then the placement shall be stop at a bulkhead or verticall form per the construction joint details provided.

 

[TXStructural]

Cold joints are characterized by the inability of cement to form its connections across the interface. If the concrete has set, you should plan on it being a cold joint. Cold joints will form accidentally between trucks in some situations (we had a major explosion and fire here in Dallas a few years ago, and there was no way to continue a large placement due to proximity of the fire itself and no roads being open to reach the site.) However, few reinforced concrete members truly rely on the tensile capacity of concrete for adequate performance, with tension in sections relying on reinforcement. Shear capacity could be a critical factor in some members, but that depends on where the cold joint happens and its geometry.

Specific to your question, slabs could be an issue if crack location will be critical or shear capacity is a controlling variable in the design.