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
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|