Autogenous Healing Limits

[Stl63]

A concrete tank was hydro-tested, damp spots appeared along the entire circumference of the exteranl base of the tank. A few spots built up enough water to trickle to the trenchs. The contractor states that this is normal and will disappear within 30 days as the concrete hydrates. The tank and foundation it sets on have been finished for 2 months prior to the test. A 6" water stop is in the foundation keyway.
Is there enough information here to state that autogenous healing will take care of the minor cracks causing these "damp spots"? From what I've read there isn't a lot of research on this topic. Any help/advice is appreciated.

 

[LittleWheels]

Autogenous healing depends on the crack width, leakage velocity and concrete mix. Wider cracks will take much longer (up to forever beyond about 0.3mm) to heal, excessive leakage velocity will prevent healing, some mixes tend not to heal (lacking unhydrated cement). There is a fair bit of research out there but it is obscure.

 

[kelowna]

At present I am working on a project with concrete that needs to be watertight. We have had and have damp spots and leaks through shrinkage cracks and construction joints. I tried to find some information on autogenous healing and ended up with some articles, not much, not very useful, I agree that the research was lacking and obscure.

However, in my case damp spots are disappearing and cracks healing (up to 0.2 mm, you can actually see cristalization inside the crack with a crack microscope) although depending on the location and problem it took quite a bit of time (up to a couple of months). I agree with DaveMinter, it seems to depend on the concrete (ours is low w/c and fly ash). It also seem to depend on the mineral content of the water and water pressure. If there is no more than a water trickle, most likely it will seal, if there is a lot of water flow it might not.
We used a couple of waterproofing products but I am not totaly sold on them.

Good luck with your water tank!

 

[Ussuri]

You could try CIRIA report C660 - Early age thermal crack control in concrete. It has a bit about autogenous healing.

or The Concrete Society Advice Note, Autogenous healing: The self sealing of fine cracks

 

[jheidt2543]

Rather than wait for the autogenous healing, I think I would coat the interior of the tank (you don't say how big it is) with a dampproofing/waterproofing agent like Thoroseal. It is realatively inexpensive, applies easily with a brush or roller and dries quickly. You don't say what the tank holds, is it potoable water? The contents may make a difference in what material you choose to coat the tank with.

It is a trade off between waiting to use the tank and getting it in service.