[TowerTalk] Rebar

[David Gilbert]

I could be wrong, but I don't think it is the water infiltration by 
itself that causes the problem.  Concrete is inherently porous and there 
are typically thousands of microcracks in it anyway.  In the open, steel 
progressively rusts in the presence of moisture because iron oxide 
requires a significantly greater volume than the iron beneath it, 
causing the oxide flakes away from the iron which then exposes more bare 
iron.  Some oxides are somewhat self-limiting, but iron oxide isn't one 
of them.  When contained within  an envelope of concrete, however, rebar 
is semi-protected from rusting by the high alkalinity of the cement.  I 
believe the problem with the larger cracks is that where they reach the 
rebar, the steel is no longer "protected" by the alkalinity of the 
cement at that spot and the steel is free to rust and expand, making the 
problem progressive.

73,
Dave   AB7E


Jim Lux wrote:
> Somewhere in between, you'll have a failed structure that is structurally OK today, but won't have the life or longevity in the future.  That's the situation where water infiltrates and causes corrosion of the rebar, then, perhaps lightning induced spalling.
>
> Jim, W6RMK