Air Entrainment with Waterproofing Admixtures

[bgsmith]

I have an exterior concrete wall that is specified to have a waterproofing admixture in the mix design. The contractor built a mock wall and with the air entrainment added they can't get a finish that the owner will accept. Does anyone know of an alternate method of waterproofing (either with admixtures or sealant and painting) that eliminates the requirement for air entrainment? Several contractors have told us that they do it but we can't find any code language or admixture approvals that would allow that method.

 

[TXStructural]

I'm guessing that the air entrainment is for frost/freeze exposure. What is the nature of the surface defects or characteristics which are unacceptable?

 

[bgsmith]

Yes, the air entrainment is for frost/freeze exposure as required for severe exposure with 3/4" aggregrate by ACI 318 section 4.4.1. The air entrainment used is approx 6%.

I have not seen the surface in question personally but the pictures indicate and the contractor is saying that the air pockets caused by the air-entrainment are visible. From the pictures there are "bug holes/rock pockets" approx. 1/8" in diameter on the face of the wall.

 

[hokie66]

Waterproofing admixture? Is this Xypex or a similar product? But to directly answer your question, you can apply waterproofing/tanking to the external face of the wall. Then you can eliminate the admixture, but not the air entraining if you need the AE for freeze/thaw conditions.

 

[bgsmith]

The admixture being used is Rheomac. Lots of local contractors are using concrete sealant or admixtures similar to Rheomac in place of air entrainment. The thought being that water won't be able to get into the concrete so it is not considered an exterior surface. I was looking for a code reference that would allow air entrainment to be eliminated if water could not penetrate into the concrete but could not find any.

 

[hokie66]

Is this the one? BASF has a number of concrete admixtures called Rheomax, with different numbers and different uses.

http://www.saudi-basf.com/en/products/Admixturesforconcrete/rheomac707/Pages/default.aspx

This one is a water reducing and plasticising agent, but is not a cure all, because no such admixture exists. The literature emphasizes that good concrete practice must be observed, and no claim is made that the admixture eliminates the need for air entraining. It does say that overdosing can increase the air content.

 

[concretemasonry]

If you are looking for a code solution, you will not find it, but many other documents can give recommendation for general use and applications.

As far as the surface appearance, that is just a matter of opinion and if it was critical, it should have been spelled out in the design criteria along with sample wall samples and panel sizes.

Apparently, you are not familiar with air entrainment. It is used for freeze-thaw resistance and and not used for "waterproofing" or create a specific architectural appearance.

Air entrainment creates very small voids and not large enough to be voids that are visible to the naked eye. It sounds like a problem with the concrete placement and vibration.

Surface coatings have a short enough life for a contractor to walk away and let the natural conditions confuse the decision where the fault lies.

Dick



Engineer and international traveler interested in construction techniques, problems and proper design.

 

[bgsmith]

Thanks for all of the input. I thought it wasn't an air entrainment problem but wanted to see if anyone else has had that problem.

I agree that using a coating may work at the time of construction but you don't have any guarantee it will be maintained.

 

[TXStructural]

Good quality concrete, which is formed, placed and consolidated is quite waterproof through the thickness. One way way to improve this in a normal placement is by using a surface-applied product, such as a silane/siloxane.

It sounds like the forms may not have been prepared properly (the right release agent is critical) and/or the mix design needs work. Appearance-grade concrete mix design should not be left to a supplier without experience with such projects. Aggregate choice and grading, and the use of SCMs and admixtures can help get a better finish. Large ready mix suppliers generally have (or have access to) personnel who can work out why the appearance is not up to requirements.

 

[Ron]

As noted, the voids are ENTRAPPED air, not ENTRAINED air. That's a placement issue, not an admixture issue.

As for waterproofing admixtures in lieu of air entrainment, they are not equal. Waterproofing admixtures will dissipate with time...air entrainment does not. The effectiveness of waterproofing admixtures to prevent freeze-thaw damage is also "hit or miss". Stick with air entrainment and add a waterproof coating on the outside if you must meet some specification for such.