Time Limit Between Concrete Placements

[abusementpark]

Is there an allowable time limit for successive placements of concrete during a monolithic pour to prevent a cold join? Are there any standards for this?

I know that it will depend on the mix, curing conditions, and whether the present concrete is being properly agitated to prevent it from setting. But I would like to get a feel for what the possible range this time limit would be.

 

[BAretired]

To prevent a cold joint, I would think you would have to place the next lift prior to initial set of the previous lift. However, it is permissible to have a cold joint by roughening the surface and providing sufficient reinforcement across the joint to resist shear.

BA

 

[Ron]

abp...check the mix design and cement certificates....don't let them go past the initial set time of the cement (usually about 2 hrs from first introduction of water to the mix). Not a hard and fast rule, but works for bonding purposes.

 

[bridgebuster]

Agree with Ron. Also, when they vibrate the upper layer make sure they penetrate about a foot into the lower layer.

 

[beton1]

Good points; nothing significant to add except it may depend somewhat on application. Say you are pouring a slab for a basement versus a bridge slab or structural elevated slab.

 

[racookpe1978]

Temperature?

Colder weather lets you a longer delay time, or a shorter?

 

[amorrison]

I think there are concrete additives that greatly extend the time before hardening.
Check with concrete suppliers.

 

[ron9876]

When the in-place concrete has set up to the point that you can't vibrate it and mix in the new pour it is too long. The time depends on many factors including humidity and wind speed. Not sure how you would come up with a time limit.

 

[ATSE]

ACI 301 doesn't provide a hard cutoff, probably due to the very many variables of fresh concrete. However, that doesn't mean you can't provide a number.
Our spec says 90 minutes max, except 60 minutes for hot weather conditions, which I believe is generous to the benefit of the contractor in most circumstances.