staggered pour for liquid retaining structure

[AskTooMuch]

Where can I get this reference about staggered pour and to wait 7 days between pours for water retaining concrete tank that is long (200+ ft)?

I tried looking for it online but can't find where it came from.

 

[hokie66]

I respect the opinions and experience of engineers like JedClampett and Rabbit12 who use waterstopped joints at 25' centres, but my opinion differs. What I have experienced is that the joints are the main problem. In a 100' long tank, if you use 0.6% reinforcement, the cracks stay water tight.

As to the table above, a construction joint is not a "full contraction joint" if reinforcement continues through the joint.

My other argument with the table is the distinction between Grade 40 and Grade 60, as regards the amount of reinforcement to control shrinkage cracking. Both grades have the same modulus of elasticity, so stretch the same amount due to applied force. If the reinforcement yields, you don't have enough reinforcement.

 

[r13]

I've just went through a concrete crack control/reducing webinar (for AIA CE credit).

Weapons for crack defense:
1) Quality mix design
2) Admixture
3) Reinforcement
4) Good construction practice
5) 1 photo provided for a long shrinkage crack parallel to a control joint on concrete pavement, with a few seconds mentioning - concrete cracks whether there is a control joint or not. Solutions - see 1 to4 above.

 

[hokie66]

AIA? Are you an architect?

 

[r13]

No. Just it is free, and "in time" of the need to refresh my mind I am pure "civil-structural".

 

[AskTooMuch]

Hookie66, you mentioned in your previous post the longer the wait the worse for shrinkage. Rabbit12 said they wait 14 days between pours instead of just 7 and I'm guessing because they think it's better for shrinkage. Completely opposite of what you said.
I'm just trying to understand this better not pointing who is right or wrong.

 

[hokie66]

My reasoning is that the first pour does most of its shrinking early, then the rate reduces. Then the adjacent pour is cast, and it shrinks. Because the first pour restrains the second, tensile stress in the shrinking second pour, which is still green, builds up to the point where cracking occurs. So one parameter in controlling shrinkage cracking is to minimise the time between pours. To clarify further, the cracking I am addressing is the cracking normal to the construction joint due to shrinkage parallel to the joint. If the concern is about shrinkage in the other direction, the answer is more reinforcement.

 

[r13]

Shrinkage won't stop at 7 or 14 days. Though the majority of plastic shrinkage is gone, then the new poured concrete will shrink for its own. For durability, uses methods mentioned above will yield better result - finer crack, if any, which is critical for water containing structures. Albeit non-technical, stretched construction time and crew schedule conflict could also be concerns.

 

[hokie66]

retired13, you need to be careful about terminology. Plastic shrinkage occurs only before the concrete hardens. We are discussing drying shrinkage.

 

[r13]

Yeah, there is no plastic shrinkage after hardened. Thanks for the reminder, correction made.