Swimming Pool Concrete Mix

[nr123]

We are currently designing an indoor pool (3'to 6'-6' deep)and have been mulling around ideas with regards to the concrete mix. Currently the pool is proposed to be shotcreted and have 8" thick walls with integral foundations and 6" slab. We are considering a 4000 psi mix with a W/C of 0.45 (564# cement content, no fly ash) and specifying that the concrete supplier provide shrinkage test results to verify the mix has 0.04 to 0.03% shrinkage. I was also considering an admixture made by Xypex (C-500) that reacts with moisture in fresh concrete and causes a catalytic reaction that generates a crystalline formation waterproofing.

Anyone have any thoughts or recommendations from their experiences?

Thanks in advance.

 

[ash060]

For the couple indoor pools I was involved with we used regular concrete and the pool contractor submitted a finish for the pool.

The finish grout product was what kept the pool from leaking. It also rounded the bottom of the pool as well. We pretty much supplied a concrete box for the contractor to put his pool in. I do not remember the product of hand.

 

[cvg]

in Arizona, land of the pool - they use shotcrete

 

[henri2]

In So.Cal shotcrete is commonly used for swimming pool construction-typically the dry-mix variety (aka gunite) for residential pools.

I assume her you are referring to wet-mix shotcrete delivered by a ready-mix concrete company...with a slump of about 2 inches maximum. That's not uncommon.

I doubt though, the typical ready-mix company will have ASTM C157 shrinkage test results of this type of mix on file. Is this a common requirement in your neck of the woods? How long will this test take to perform and how much will it cost? I used to perform them back in the day (usually for CIP post-tensioned slabs or admix qualification tests) and recall charging a pretty penny.

 

[cvg]

you should have no trouble getting 3 - 4% shrinkage at 28 days. Probably no reason to do any testing. After the first year, you will probably have way more than 4%. If you really want to reduce shrinkage, recommend you lower your w/c ratio and optimize the coarse aggregate size. See attached document for more information.

 

[IRstuff]

The OP stated 0.03% not 3%, unless that's a typo.

TTFN

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[ATSE]

cvg probably meant 0.03% = 0.0003 for concrete shrinkage.

Unless you have a compelling reason not to use fly ash, use 15% - 25% fly ash (cast-in-place or shotcrete).

Cracking in swimming pools has more to do with the delay between end of curing and when the pool is filled.
For 100% relative humidity (water-filled pool) and a well designed concrete mix, concrete shrinkage will be very small per ACI 224 Fig 3.3.

Leaving a swimming pool unfilled (which the engineer has little control over) increases the likelihood of measurable cracks.