Precast panel drying zone

Michael Hurd · Post by **Michael Hurd** » Mon Mar 14, 2011 11:32 am -1100

OK, I'm going to try submitting this as a new topic to see if someone will respond to me???I am trying to model an exterior precast wall panel where the panel sandwiches the insulation between two sections of concrete. Here is the actual make-up: 3/4" thin brick (placed in the panel form before pouring the concrete) followed by a 2" face panel concrete, Then 2" of extruded polystyrene and finally 4" of concrete to form the back of the panel. In light of the paper written regarding the hygrothermal properties of concrete exposed to weather, I'm wondering if this concrete panel will behave in the manner described in that paper or if having a thin face brick on the precast panel would prevent the precast panel from forming the "drying" zone described in the paper on your website. A second question would be if the precast will develop the "drying" zone, the dimensions of the face portion of the panel do not really allow for the 70 and 80mm zones described in the paper, so I wonder how to treat this condition. As always, I look forward to your input!
The paper I refer to is on your website titled Hygrothermal properties and behavior of concrete by Kunzel Holm and Kruz -WTA almanach 2008

Daniel · Post by **Daniel** » Wed Mar 16, 2011 6:16 am -1100

Dear Michael,

I'd assume that the concrete layer is too thin to get a "self sealing effect" in the pores.

Did you try to simulate the wall with and without liquid transport - maybe the difference is not that big? Please use the concrete w/c 0.5.

What problem do you fear in case of some moisture accumlation? Corrosion of the conrete reinforcment or increased heat conductivity in the Polystyrene boards?

best regards
Daniel

Michael Hurd · Post by **Michael Hurd** » Wed Mar 16, 2011 7:13 am -1100

Daniel, I did not try simulating the wall with and without liquid transport, that is an excellent suggestion. I guess I was concerned that increase diffusion without the drying zone could lead to some moisture build up inside the steel stud and gyp board furring that will be placed on the inside face of the precast wall assembly - I will model as you suggest and see what happens. Just out of curiousity, why do you suggest concrete w/c 0.5? Others have suggested to me that the C35/C45 concrete is a better selection for simulating precast panel concrete. Thanks for the response by the way.

Daniel · Post by **Daniel** » Wed Mar 16, 2011 9:20 am -1100

The liquid transport of concrete is always difficult to measure due to the swelling of the pores.

The measurements for the C34/C45 seem to be a little bit on the safe side (with a stronger liquid transport). But in comparison to field tests we found a good agreement by using the w/z 0.5 concrete.

But in fact it's maybe the best idea to use both concretes for your simulation - then you should be on the safe side for all scenarios. It's always a good approch to vary all uncertain input data to check their influence.

best regards
Daniel