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.

 

[r13]

I suggest to provide keys and water stops to prevent leakage from crackjoint.

 

[oldestguy]

Whether or not you find the reference, keeping your w/c ratio down will minimize the shrinkage. Seven days generally refers to when you can place load on it, since a good portion of the ultimate strength is there by then.

 

[hokie66]

There is no reason to wait 7 days between placements at a construction joint. To the contrary, if shrinkage cracking is the issue, the longer you wait, the more differential shrinkage.

 

[AskTooMuch]

See response from similar thread. I'm not basing this question from this response alone.
I've been told about it although the engineer who told me can't say where it came from except it's "common" practice in the liquid retaining structure design.

"JedClampett (Structural)
12 Jun 14 16:11
I would leave out control joints, too, unless the reinforcing passes through them.
Pour in 25 ft long sections. Pour the slab in a checkerboard and wait 7 days between adjacent pours. Same for the walls."

 

[AskTooMuch]

By the way, I'm not doing the actual engineering/design. This is just for my information.

 

[r13]

If concrete pour can't finish by the same day, I think you guys need to plan ahead, may need to add joints, which is not desirable for water retention tank. I suggest look into ACI and PCA for recommendation on concreting.

 

[AskTooMuch]

Absolutely no relation to not being able to pour same day. You can line up concrete trucks and can pour long walls or slabs in one day. I've personally seen this done.

This is a crack/shrinkage thing.

 

[HTURKAK]

AskTooMuch (Petroleum)
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)?

Although it is not clear whether it is a construction joint or not but 'staggered pour and to wait 7 days between pours' implies the concern is the construction joint at slab . In order to provide adhesion between the two concrete faces , the face of first placed section shall be prepared (the surface laitance will be removed ) with sand blasting, scabbing ,or ultra high pressure water jetting.This treatment should be carried when concrete is 7 days old.

In case of EJ, Contraction J...(with water bar provided ),it is not necessary to wait..pouring the next day is possible.

 

[r13]

AskTooMuch,

That's how we did for a hydroelectric powerplant construction - setup onsite mixing plant and pump concrete around clock until a flat lift (3'-4') is finished, no cold joint is allowed. Lift keys and water stops are installed around perimeter to seamlessly connect the upper lift. Same setups for the vertical lift that has lift height limit.

But it seems you are challenging, or to confirm, someone said something like "wait 7 days for the next pour won't have bad consequence", I can only say it is wrong, since the cold joint is the primary source of cracks and leaks, not to say you have two pours with different shrinkage rate.

 

[AskTooMuch]

Retired13,

If I have a 100' long wall that construction confirmed can be poured monolithic, do I need construction joint? I was told I need it.

If you see Jed Clampett reply, he limits to only 25' long between construction joint.

This is new to me because I thought you put construction joint because you can't do one pour. Not as a sort of equivalent to "contraction" joint for liquid retaining structure to prevent cracking.

 

[Rabbit12]

AskTooMuch, we limit our pour lengths to 25' too but we require 14 days between adjacent pours. I would highly recommend not pouring a 100' long wall in one continuous pour.

I'm not sure if these requirements are from some code or if it's just years of experience.

 

[HTURKAK]

If I have a 100' long wall that construction confirmed can be poured monolithic, do I need construction joint? I was told I need it.

If you see Jed Clampett reply, he limits to only 25' long between construction joint.....

Dear AskTooMuch (Petroleum), what are the dimensions and thickness of slab and walls of the tank? you said (200+ ft) first then 100 ft...
Is the tank buried? What is the ambient temperature? ..

My first suggestion was for the slab...In order to provide structural continuity , the reinforcement shall be fully continuous across the construction joint and shear friction check shall be performed at a construction joint.As per ACI 318 -14 ( 22.9.4.2) nominal shear strength across the shear plane shall be calculated:
Vn = μAvf fy
μ is the coefficient of friction in accordance with Table 22.9.4.2. (which is shown below).

The table clearly shows that, concrete placed against hardened concrete that is clean, free of laitance, and intentionally roughened is better than other options if construction joint is provided.

My suggestion will be, if the dimensions 100ft W X 100ft L, the base slab could be single pour , provide PE film below the slab..and regarding the walls;considering 100 ft wall ; 25 ft pours suitable. One of the vertical joint should be EJ. The others CJ.and waterstop shall be provided for vertical CJ, EJ ,and horizontal CJ with slab..

 

[r13]

AskTooMuch,

I don't know where is the 25' joint rule came from, and the reason why the 100' wall can't be poured by one lift (to the lift high limit), if the form work is capable of taking that pressure, and properly/continued vibration can be practiced. Our practice is to pour the wall on one segment to allow time for adequate vibration, the pour continues at adjacent location, then come back to finish/bring the earlier segment to the specified lift high limit, the staggered pour sequence continues until finish. Sometimes the return is delayed, and the previously poured concrete surface appears dry, then mortar with the same strength should be added, and vibration must penetrate a few inches beyond the joining surface to ensure the two concrete pours form an integral product. I would love to know the source of the lateral lift length/distance limit though.

 

[Rabbit12]

The same reason you wouldn't pour a 25'x100' slab without cutting in control joints. Shrinkage cracks aren't a good thing in a water retaining concrete wall.

 

[r13]

There are ways to compensate for shrinkage effect, by additives, low W/C ratio, concrete temperature control during placement to slow down rate of heat hydration, better/proper curing, closer spaced reinforcement, and lastly, cutting control joints. It is admittedly the horizontal lift length has a practical limit, but number of joint should be kept to the minimum, or avoid, for water retention tanks.

 

[Rabbit12]

retired13, I'm not going to argue with you because you seem to think you're an expert with everything.

My last thought on this subject. My company has literally done 100's maybe even 1000's of water retaining structures and this is the practice we use. We limit wall pour lengths to 25', provide a waterstop at the joints and require a wait time of 14 days between adjacent pours.

AskTooMuch, sorry I don't know where our requirements come from. If you really need a source I can try to ask around and see if there is something codified or if this was just developed based on years of experience.

 

[JAE]

Rabbit12 - with your typical practice - how do you deal with ACI 350 where they require higher levels of horizontal reinforcing depending on distance between expansion joints? (section 7.12.2.1).

It seems that your practice of using 25 ft. segments "sort of" circumvents the basis of the table outlining higher and higher reinforcement ratios for longer lengths.
So if you had a 100 ft. wall and built it with the 25 ft. segment method, do you still use Table 7.12.2.1 and 100 ft. to determine rebar?

Granted - a 25 ft. spaced construction joint is not a "movement joint" per se, but it does remove a lot of the shrinkage. If this table is based on thermal response only then perhaps the 25 ft. CJ spacing is more a common sense response to reducing initial shrinkage only.

 

[Rabbit12]

JAE, good questions. For our 25' wall segments, we use a minimum reinforcing ratio of 0.0030 per the table. The note says the table applies to "full contraction" joints so in our interpretation our construction joints are contraction joints.

If I had to guess why we limit the pour length to 25', I'd say it's so we can provide minimal reinforcing (0.0030 unless more is required per analysis) and not be at the upper limit of these requirements.

 

[r13]

retired13, I'm not going to argue with you because you seem to think you're an expert with everything.

No argument here. You are the expert on this topic. But I wonder where is the shots coming from!