Waterproofing Underground Tank for Wastewater 2

[Struct_Dre]

Hello All

I'm working on the design of a few underground tanks and I need to know how to specify what kind of waterproofing should be used. Could someone provide the requirements for waterproofing an ACI 350 underground tank? After some googling, I found that ACI 515.1R-79(85) probably has what I need, but I don't have access to it.

Any help is appreciated!

 

[JStephen]

I thought the idea was that the waterproofing was built in via reduced service level stresses and limitations on bar spacing, detailing, etc.. Section 4.7 addresses liners and coatings, but seems to be intended for corrosive products, not for waterproofing in general.

 

[Struct_Dre]

@JStephen Thanks for the quick response! That would definitely explain why I haven't been able to find much information on it. I've done waterproofing before, but on a much larger structure.

 

[Struct_Dre]

Ok! So I did some more digging and talked to a senior engineer at my firm. The rule of thumb is "include waterproofing when you need to stop water from getting in or out of the structure." Haha which seems very obvious. ACI 350 structures are supposed to be watertight so I assume waterproofing is needed. Also, my tanks hold raw water which absolutely should not leak - so waterproofing is required. I was able to find a specification used on another job.

I hope this helps anyone who had the same question as me!

 

[JoelTXCive]

Try this link....... you can hopefully view the ACI document on the Scribd website. I think to download requires a membership:

https://www.scribd.com/document/148398991/ACI-515-1R-pdf

Link

 

[EDub24]

I’ve designed many tanks for wastewater treatment plants and I don’t think I’ve ever used waterproofing membranes. I usually have PVC waterstops at all joints and a tight rebar spacing to control cracking. Sections 6.4.7 and 6.5.2 direct you to use waterstops when the structure is supposed to be watertight. In my experience, waterproofing membranes degrade over time so you shouldn’t use it as your main means to have a watertight tank.

 

[Struct_Dre]

@EDub24 Thanks for the help! I am using PVC waterstops as well. You're right, I've done a lot of tanks and I've never used waterproofing, but I was told by a senior engineer at my job that it may be necessary due to the raw water. I was hoping I could find a definite answer in some code, but I haven't had much luck.

I'[m thinking that waterproofing may not be needed, but I'd rather be conservative.

 

[AskTooMuch]

Being conservative is not always good. It could drive construction cost up and make client angry because of "over engineered"/ expensive design.
I checked an existing raw water pump station concrete sump drawing we have and didn't find any type of waterproof membrane.

 

[Struct_Dre]

@AskTooMuch Thanks so much! Ok, it sounds like I won't be using a waterproofing membrane. I'm a newer engineer, so I sometimes second guess myself when senior engineers at my job tell me something different than what I know. This forum is super helpful.

 

[JLNJ]

For a rather minimal cost you can specify admixtures in the concrete mix to help lower the concrete's natural porosity.

We have spec'ed Xypex products in the past for things like industrial waste lift stations.

 

[TehMightyEngineer]

It helps to know what the use of the structure is? For many precast concrete structures I can easily meet ACI 350 and get a nice waterproof structure without anything fancy; just nice dense high-strength concrete and plenty of reinforcement.

However, depending on the job, I've also had plastic membranes used, interior coatings, exterior coatings, joint wrap, PVC water stops combined with hydrophilic waterstop, joint sealants, silane coatings, etc. It really depends on the usage, durability requirements, flow, what's being contained (is it acidic?), budget, etc.

All said, 80% of the ACI 350 structures I've designed are just plain, high-density concrete.

Ian Riley, PE, SE
Professional Engineer (ME, NH, VT, CT, MA, FL) Structural Engineer (IL, HI)

 

[TehMightyEngineer]

For a rather minimal cost you can specify admixtures in the concrete mix to help lower the concrete's natural porosity.

This is probably the simplest budget way to ensure better liquid retention and durability for an ACI 350 structure in my opinion. Go precast or use an admixture like JLNJ mentioned. If you want to be really fancy add specification requirement for concrete permeability testing; but of course such testing adds cost to a project. I'd probably just specify minimum w/c ratios to target a low-permeability concrete.

Ian Riley, PE, SE
Professional Engineer (ME, NH, VT, CT, MA, FL) Structural Engineer (IL, HI)

 

[GC_Hopi]

JStephen and others hit the head of the nail. ACI 350 is the go to for design on water containing structures. In the summary it states "Such structures are used for conveying, storing, or treating liquid or other materials such as solid waste...produce serviceable concrete that is dense, durable, nearly impermeable, and resistant to chemicals, with limited deflections and cracking. Leakage must be controlled to minimize contamination of ground water or the environment, to minimize loss of product or infiltration, and to promote durability."

Coating are a specialized product and as such are used in particular circumstances mainly when the reinforcement needs protection from chemical attack. They are not end all/be all solution for environmental structures.