Saltwater pool

[bnickeson]

Has anyone ever done the structure for a saltwater pool before? We were tasked with designing the containment walls for a rooftop pool, where the EOR already designed a big tank for it and we designed the supplemental walls for the pool that sit inside the main tank. The owner just changed this to a saltwater pool, where salt is converted into chlorine and it results in a salt content in the water about 10% of what you'd find in the ocean. So it's not terrible but it's still present.

I am wondering if there's anything additional I have to do for this pool design now that saltwater has been added. I already used ACI 350 as a guide for the wall design, so I'm using a fairly tight rebar spacing, 4500 psi concrete, and 0.42 w/c ratio. Are there additional additives I should use in the concrete? Sacrificial anodes? The pool will have a plaster coating if that makes a difference.

Thanks.

 

[XR250]

Isn't chlorine just as corrosive?

 

[Tomfh]

Sufficient cover is the main thing. Standard is 65mm (2.5 inches) or thereabouts, eg 150 wall with a central layer of steel. Plaster whilst not counted as cover does provide additional protection, especially at cracks, where water and chlorides can get to the steel.

Pools tend to rust where the cover requirements have not been achieved. Sacrificial anodes are fairly uncommon, at least in Australia, where most pools are salt.

 

[Tomfh]

XR250,

Chlorine pools are corrosive, however salt pools are more corrosive, followed by sea water, which has 10x as much salt again.

 

[bnickeson]

Isn't chlorine just as corrosive?

From everything I've read, no, saltwater is worse. Of course, most of these write-ups I've found are addressing the pool parts and components rather than the concrete and reinforcing, but I'm assuming that the same applies to the structure.

 

[hokie66]

‘Salt pools’ are sanitized with chlorine. The chlorine is produced by electrolysis from a relatively low level of salt in the pool. The key thing in preventing deterioration of the concrete and to maintain the health of the pool is to control the pH. Look after the chemistry, look after the pool.

 

[lexpatrie]

It's so odd that thinks I run across somehow show up as a question like a week later.

I suppose it depends on if you're trying to do a standard effort design or going beyond that. You didn't mention the extra load factors but you did mention ACI 350 already. I'm not positive this code applies, it's intended to be for water and wastewater treatment facilities, and some of the things in it are about crack control to prevent/reduce leakage, which given the location, might be wise to consider, but perhaps not strictly necessary if you're willing to let it leak more than an ACI 350 structure (and in a not quantifiable way, I'm not convinced they ever compared a non ACI 350 leak rate to an ACI 350 leak rate, but I wasn't involved in the standards process, I just ran into it for WTP/WWTP back around 2000.

If I recall correctly there's a list of chemicals that affect the mix design, I had a project with (I think) potassium permanganate and that's mean to concrete. I think that list was in ACI 350.

This might be useful - but it's pretty old - Suprenant has had some articles I've considered in the past.
Designing concrete for exposure to seawater, Suprenant, Concrete Construction, December 1, 1991.

There are a fair number of additional articles, I searched for "seawater" and got guite a bunch. Sounds like what you have is "less" than seawater, but it may be reasonable to apply it in absence of any other information that refines it.

This is sorted by relevance, if you sort by newest the first page is a lot about desalination and sustainability.

https://www.concreteconstruction.net/search?q=seawater

ETA - I forgot the article I was talking about at the top.
Corrosion of Coated and Uncoated Reinforcing Steel in Concrete - Lorentz, French, Leon, Center for Transportation Studies, May 1992.