Intregal Concrete Admixture WaterProofing In Elevated Slabs?

[StructuralEd]

Anyone use concrete admixture "water vapor proofing" in elevated slabs?
The concern presented is in regards to flooring failures in new construction from slab moisture content.

 

[Ron]

In my experience, they don't work.

 

[TXStructural]

I have not correlated admixtures to adhesion failures of coatings and floor coverings, but if the admix retards drying of the concrete, there could be lingering moisture which would cause such a failure. I bet the RapidRH meters would work. You drill a hole, set the meter in the hole, and let it sit long enough for air in the void to equilibrate. (They reside in the hole for as long as the problem persists, or until the RH is low enough to allow continued construction.)

 

[rscassar]

Never actually specified one but xypex has a product

 

[StructuralEd]

I didn't want to list names but one product begins with a "B".
I believe that it is supposed to greatly retard moisture movement both in and out of the concrete.

A client who has had many moisture problems is interested in integrating it in all floors, both on grade and elevated.

I have concerns if it might not be metal deck friendly, both in itself and due to the retained moisture. And then there is the question of bond to composite decks.

 

[hokie66]

The title says "waterproofing", but you seem to be talking about some sort of vapor barrier. Different things.

 

[Ron]

Look at the fundamental science of this....

Water is necessary for hydration of cement. If a "waterproofing admixture" or vapor reducing admixture is used, it must be something that reacts with the remaining moisture in the concrete after hydration occurs. This is often done with calcium silicates applied to the surface of concrete after sufficient curing....they produce void-filling calcium silicate compounds from the inherent moisture in the concrete...surface "hardeners" if you will.

The other approach is something to encapsulate or isolate the moisture within the concrete as hydration occurs. This is the premise of a "waterproofing" admixture such as Xypex or similar. How much of the moisture can it bind and how much can it leave available for hydration?

Answer this question and you can decide if a "waterproofing" admixture works or is even appropriate.

 

[Forensic74]

Using the fundamentals, waterproofing can be done with an admixture that clogs the pore network. Check out soy methyl ester.

OR if you dont want to risk weird reactions with metal or the surrounding environment just use a hella low water to cement ratio. It's as good as waterproofed. Permeability goes way way down. Sounds like this is a good job for a concrete consultant to recommend the right mix.

 

[hokie66]

Quality concrete is reasonably water-resistant until it cracks. Xypex and other similar crystal forming admixtures can clog small cracks, but only in the presence of water. So you need a leak first, then the crystals form. This philosophy always seems backwards to me.

 

[StructuralEd]

The issue is not water resistance when talking about elevated slabs.

This is about the moisture content of recently poured slabs creating floor finish bond failures. Apparently there is concern for potential problems long (6 plus months) after placing the concrete. Widely variable test results have elevated the insecurities.

 

[Forensic74]

At 6 months I would be more concerned with the RH of the ambient air rather than anything you could do with the mix design. If its curing in Florida or some humid environment, then the internal RH of the concrete will equalize to that unless you have a low enough w/c to self desiccate.

 

[StructuralEd]

What I read one one admixture: fills the capillary system with calcium silicate hydrate by reacting with water and alkali eliminating moisture migration.

Would this have long term effect on the concrete, metal deck or reinforcing materials or bond?

 

[mfrad]

The pH of concrete is high causing an alkaline environment to occur that is not friendly to floor adhesives generally causing debonding. Metal deck is impervious especially if there are no vents (hanger tabs) provided to release moisture downwards. The flooring is also has low perm ratings so the excess water from the concrete mix drying out can't escape and is trapped causing floor failures.We generally wait six months before applying finishes. Longer if you use lightweight concrete aggregate.

 

[SkiisAndBikes]

Coatings have successfully been put on elevated slabs for years without "water vapour proofing" admixtures. I would be more inclined to look towards the concrete mix, placement/finishing procedures, surface preparation and timing of coating installation. All have been implicated in past coating failures.

We have bond tested waterproofing coatings on concrete slabs and achieved bond strengths in excess of 1.0 MPa (145 psi). If you have good surface prep and good environmental conditions during installation and can achieve at least a 0.6 MPa bond strength at installation it unlikely to debond due to vapour pressure in the future. Vented deck may reduce the chance of vapour pressure building up behind the membrane/coating.

In the past, we have specified vented decking, however, see below link from the Steel Deck Institute which tends to discount the effects of venting and hanger tabs.

http://www.sdi.org/papers/PPVENT.pdf

 

[Brad805]

Kryton and Xpex both work very well for waterproofing. They work for cracks up to 0.5mm wide, so you do need all the rebar you do for any watertight design if waterproof is the goal.

Both versions retard your set time greatly even though neither manufacturer wants to talk about that. I even used it in my own personal elevated slab, and the finisher waited from 8am until 2am the next day before he could get on it. The set time is a bit problematic for wall forms as we have learned.

Brad

 

[hokie66]

Brad,
Setting time is not the only thing these manufacturers don't want to talk about. The necessity for extensive crack control reinforcement, as you pointed out, was formerly emphasized, but now is not. I have investigated several leaking decks where dependence had been placed on Xypex, only to have big problems with leaks onto the expensive cars below. The crack control had been neglected.

 

[Brad805]

hokie, so many times I have come in after one of the so called wonder products have been applied. None of them fix the structural problems related to inadequate bar.

I recently received the new Kryton magazine and was surprised to see they are suggesting using the KIM in an ICF form. We get involved in a lot of ICF's and know how important the form pressure is. I cannot imagine how they can do this for an ICF form. Form blowouts will be a huge problem if they fill an 8' tall form, and it will only get worse after that.

Brad

 

[Ron]

When silicate forming admixtures are used in the mix, they must be weaker than the silicate forming additives placed after hardening and curing. The formation of calcium or sodium silicates results in expansion, so if the concentrations are high enough to fill all voids (assuming adequate and consistent dispersion of the material), they will damage the concrete in the early stages of curing (typically causing dusting/scaling).

If the dosage is low enough to prevent damage, it will not fill the voids appropriately.

Use other means to "waterproof" concrete.