Cold Joint Timeframe

[cancmm]

Is there any guidance on the maximum allowable amount of time that can elapse between consecutive pours in a monolithic structure? The purpose is to see if a cold-joint has formed after a significant delay between concrete trucks. The allotted time would obviously depend on the type of mix, admixtures, weather, etc. but I'm not sure of how to quantify the time in any way.

 

[SlideRuleEra]

This is a good question. I don't believe that there is a direct answer because of the factors you mention. However, for the "guidance" you requested there may be a way around those details:
In the US, concrete must be placed within 90 minutes per ASTM C94, as referenced by ACI. Therefore, IMHO, 90 minutes is the MAXIMUM allowable delay.
See these threads for discussion of the 90 minutes time frame (120 minutes in the UK).
thread581-82924
thread167-225769

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[dkite007]

The above reference is to "place" concrete. After placement there could still be a considerable time before the next lift.

Ambient temp and mix design are your two main factors determining when a cold joint will form. Are additives used to delay the set time?

As a rule of thumb, if the concrete can no longer be easily vibrated and mixed with the new concrete, a construction joint should be considered. It's really a judgement call, which is why you probably don't find too much info for exact specifications.

BTW, with certain admixtures, you can easily go up to 120 minutes prior to "placement".

 

[HeavyCivil]

I agree that it will vary greatly and that the condition of the concrete should dictate.

If it is still plastic and the vibrator sinks to the bottom, mixing lifts (or sequential pours in flatwork) then I dont think there is a problem.

Unfortunatley, in flatwork anyway, by the time the concrete is no longer workable its way too late to install a bulk head and come out with a clean joint.