leaking concrete watertank 4

[structural87]

Hi,

I am facing a problem with a circular concrete watertank which is leaking (diameter around 10 meters and height around 20 meters).
Many longitudinal cracks are visible from the exterior.
No as built drawings for the stucture are available with the client.
The cracks measured looks between 0.4 and 0.6mm.
It will be a big mess to repair the cracks from inside and outside since there are really many and it will mean emptying the watertank for a long period of time.
The contractor is proposing, instead, to apply a PVC membrane in the interior instead of doing the repair works. The type of the membrane and its thickness are under study right now.

I would like to have your opinions.

On a side note, for water retaining structure equipped with a waterproofing membrane, what is the maximum allowable crack width ? 0.10mm without liner and 0.4mm if liner is provided ?

Thak you.

 

[dik]

Can you use a liquid rubber like material similar to Ames Blue Max? I've not used it, but have used 'Blue Stuff' from Bakor in past and I don't know if it's still available. Was an excellent product.

Dik

 

[briancpotter]

How old is this tank? If it's new and being filled for the first time, the smaller cracks may self-seal.

Brian C Potter, PE
Simple Supports - Back at it again with the engineering blog.

 

[structural87]

It is almost 20 years old. The cracks were always there. a Thick membrane was applied initially at the time of construction.
Looks like that they were doing some renovation works for the membrane and used a new one which was not successful.

 

[briancpotter]

JedClampett is a good source of information on concrete tanks, liners, and repairs.

Here's a couple threads discussing possible solutions: Thread1, Thread2

Brian C Potter, PE
Simple Supports - Back at it again with the engineering blog.

 

[JedClampett]

When you say longitudinal cracks, do you mean horizontal? Because normally, tanks crack vertically. But my approach below will work either way.
Well, as far as applying a PVC membrane, that is going to require emptying the tank for a considerable time. Plus with a liner, you need to provide details to seal any outlets, which is a nuisance and takes more time.
If emptying the tank is not an option or is just a pain, I'd use divers. The tank is not that large, it's probably a couple day job for two divers. They go in with dye wands, and if there's a leak, they can immediately follow with a hydrophilic injection material like SikaFix HH. The flowing water will draw in the injection material and it will swell up almost immediately. The diver can check with the dye wand if the leak is stopped. The results should be noticeable right away. You can have them wear video cameras and watch the whole thing, like a football game.
Note that any swelling material has a lifetime, but as long as it's not disturbed, you should get 10 to 15 years from it.
If the cracks were vertical, you could post tension the tank from the outside and shotcrete it. This would likely eliminate 90% to 95% of the problems. But I'd want the tank to be empty during post tensioning.

 

[structural87]

i meant vertical cracks Jedclampett ! thank you for your answer !
Post tensioning isnt an option ! I will try with the divers thing !
regarding my question of limiting the crack width, is 0.4mm an acceptable crack width if the tank is equipped with a liner ?

 

[JedClampett]

Well, a .4 mm crack all the way through will leak. A lot. But if you have a liner, the liner is the leak proof membrane, so the crack size is not really applicable, except that the liner needs to span over any really wide cracks. And .4 mm is not that wide.

 

[structural87]

Thank u again Jedclampett !! A liner can be a coating or a membrane, right? I mean that i dont think any difference exist between a coating or membrane as long as it is correctly applied !

 

[JedClampett]

You'll find that a membrane installer will stay until it's right and a coater will have excuses until you're tired of them.
They should work the same, but if all else is equal, I'd prefer a membrane.

 

[epoxybot]

224R-01: Control of Cracking in Concrete Structures (Reapproved 2008) supplies a chart of tolerable crack widths for various exposure conditions. I no longer have even an old set of ACI Manuals, so I can't say what written guidance accompanies the chart. You can see the chart in this thread. Link