Reinforced Concrete Crack Control 1

[ypzhang]

Hello Everyone!

I am working on a project related to the reinforced concrete water tank crack control recently, the concrete tank is not allowed to have any crack.

Does anybody have related examples about calculation of crack control? (examples that no crack is allowed)

Thank you very much!


Best regards,


Tom

 

[civilperson]

All concrete cracks, small cracks are superior to large cracks.

 

[msucog]

"All concrete cracks, small cracks are superior to large cracks."...lol...i may need to borrow that quote...i believe that's the funniest thing i've heard all week.

contact a material engineer, local batch plant and/or local testing firm for assistance with controlling the mix to help minimize cracking. as far as design and calculation of cracking, i'll have to defer that to someone else since i'm not familiar with a reference that thoroughly discusses this concept.

 

[dochardnose]

1. Consider post tensioned concrete.
2. Consider the use of a shrinkage reducing admixture, "SRA". SRA's are available from BASF Admixtures (Master Builders) or WR Grace.
3. Consider installing joints with waterstop and sealant. (Geni or Watson Bowman Acme).

 

[SlideRuleEra]

See "Watertight Concrete", an out-of-print document from the Portland Cement Association. A .pdf version is on this page of my website

http://www.slideruleera.net/PCA-Page.html

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[JedClampett]

Who says the concrete can't crack? Just because there are cracks don't automatically mean leaks.
If there is a quarter inch crack clear through the wall, it will leak. If there is a .001 inch surface crack, it won't leak. And if the cracks have waterstop, they won't leak.
And here's a dirty little secret. Sometimes initially leaky walls stop leaking through clogging or calcification.

 

[asixth]

I would get a hold of a water retaining design guide, this should give some recommendations on reinforcement ratios. It is my understanding that providing more reinforcement will minimise the width and frequency of cracking.

 

[patswfc]

What design code are you using?

In the UK the code for concrete water-retaining structures allows cracks up to 0.2mm. With cracks of this size there may be some initial leakage, but these will self seal through the process of autogenous healing.

If your code/client permits no cracks what so ever then you'll have to use a prestressed concrete solution.

 

[asixth]

AS3735 'Liquid Retaining Structures Code'...

I'll have to read it tomorrow to see what the crack width limits are? I never understood why crack widths are codified because there are a lot of uncertainties when it comes to calculating crack widths. I think a lot of it comes down to an experienced engineer who has been lucky enough to inspect their design's to get a good understanding on what crack widths should be expected.

 

[nuche1973]

You could look into using fiber reinforcing to controll suface cracks. Companies like Propex have several different sizes and lengths of fiber reinforcement. Although I believe that they are intended for use in slabs-on-grade. Just a thought.

 

[edwin17th17]

Aci 350 has provisions for crack control.. i wonder why no one has mentioned it..

 

[JedClampett]

The reason no has mentioned ACI 350 is that there is a difference between crack control and crack elimination. If you go around promising your design won't crack at all, you're going to have to do some back tracking after construction. I heartily recommend using the provisions of ACI 350. JUST DON'T EXPECT THAT A TANK ISN'T GOING TO CRACK. IT MIGHT NOT LEAK, WHICH IS DIFFERENT.
I'll rephrase something that has been said numerous times in this thread:
"Concrete is going to crack. The best we can do as structural engineers is to plan for the cracks like we know where they're going to occur."