What is the capillary tendency of concrete?
I was at a seminar the other day and the presenter, who is a civil engineer and self-proclaimed building science expert, made a statement that caused me concern. He was contending that a vapor barrier is not necessary under a concrete slab on grade because in order to get vapor transmittance through the slab, the vapor pressure would have to be greater than the compressive strength of the concrete (i.e. 4000 psi concrete would need greater than 4000 psi of vapor pressure to move vapor through it). I would like more opinions on that please.
He also dismissed the need for a capillary break for similar reasons but moved on to other topics before explaining it much. I am assuming (which I shoudn’t) that he supposes a course aggregate base to relieve any capillary action before it reaches the slab, but I am not sure. In the end he specifically said a capillary break between the footing and the foundation wall was pointless. Comments on that are welcomed also.
So what I would really like to know is how prone to capillary action is concrete, and is it affected at all by the design strenght of the concrete?
Lots of questions in there actually, but opinions (or science) would be appreciated.
Elden in Duluth.