[TowerTalk] Concrete; Abosrbs water? Porous?

[Jim Lux]

At 03:38 PM 4/28/2005, Pat Barthelow wrote:
>Jim Said:
>>Almost all standards call for the rebar to be completely inside the
>>concrete for just this reason.  You don't want a small crack exposed to
>>allow water to infiltrate with capillary action.
>>
>>Jim, W6RMK
>
>I may learn somethng here.....It is my gut level impression that buried 
>concrete in wet or damp ground absorbs moisture.  Isn't concrete porous, 
>easily absorbing water thorugh it's contact surface with wet ground?
>
>73, Pat aa6eg at hotmail.com
>
There's a difference between interstitial pores and a continuous crack.  In 
a continuous crack, capillary action can draw liquid into the crack.  Some 
theories of weathering of rock maintain that this is more significant than 
the oft mentioned "freeze/expand/crack" mechanism.

The thin crack problem is particularly pernicious if there's any ability 
for flow, because a continuous flow (in the over the years sense) can 
continuously leach minerals out, or bring fresh water in to corrode metal.