[TowerTalk] AN Wireless tower

Mon Sep 17 01:01:30 EDT 2012

So in a nutshell moisture passes through concrete, right??  And if you 
don't think that concrete doesn't absorb moisture in the absence of 
significant microcracks, just
drop a chunk of it in a container of water for a short while and see 
what happens.  Hint:  lots of bubbles and it's heavier when you take it 
out than it was when you put it in.  How do I know this?  I've done it 
when I needed to cut pieces of concrete and didn't have a wet saw.  It 
works very well.

Regarding the treated wood against concrete slabs.  Code requires that 
for all interior walls as well, not just the exterior ones, and it 
requires it for the reasons I stated.

Just curious ... what discipline is your P.E. for anyway?

Dave   AB7E

On 9/16/2012 9:30 PM, KR7X wrote:
> Dave:
>
> The comment was meant to make you think about what you purport to say is
> true when it is not, in the context you use.
>
> Concrete does indeed have pores and they are very small in relationship to
> the volume of the sample you consider and do not necessarily line up to form
> a conduit for moisture intrusion. Concrete is also alkaline which tends to
> inhibit acidic attack and sulfate ion corrosion. The full reason that there
> is a requirement for the spacing of the reinforcement is to help with the
> moisture intrusion from micro cracking which takes place when the concrete
> cures and resists loads. This is also the reason that the code clear cover
> differs from concrete cast against soil (3"), cast in form exposed to
> atmosphere (2"), and cast in form and indoor exposure or top of slab
> (varying from 1 1/2" to 1" depending on bar size).
>
> The moisture does not travel through pores, it will travel through micro
> cracks. These cover  values were determined over the years by examining the
> in place behavior of real work concrete in various climates, locations, and
> types of structures or purposes. Curious thing about concrete is for it to
> work as a design intends it has to crack (very small and not always in
> organized pattern), this means that the load is being resisted and the
> forces ( stresses) are be resisted. It is these cracks that the cover
> requirements are meant to mitigate so that free air and moisture do not
> reach the reinforcing which would tend to corrode. When the bars corrode
> they swell and further crack the concrete exposing more and more surface to
> the free air and moisture and so on.
>
> Not pores (or porosity as you allude to).
>
> Your treated wood example is also not quite accurate, treated wood for floor
> plates is due to the fact that the inside of stud walls have varying
> humidity due to the moisture content of the wood framing members when it is
> originally constructed. The inside wall covering and the more modern used of
> a vapor barrier (TyWrap) on the outside over the base exterior siding under
> the outside finish effectively seal the wall cavity and there is (due to
> temperature differentials) a tendency for the moisture to collect at the
> base of the wall. The treated plate  helps the wall maintain is integrity at
> the base by resisting rot (dry and otherwise) and/or  softening so the wall
> does not pull away from the required hold down anchors or bolts when loaded
> laterally.
>
> I see that you have your beliefs and concepts about why things are required
> and I have mine and it is probably best that this discussion be taken off
> this reflector so a more tower specific topic can be addressed.
>
> Regards
> Lonberg Design Group, Inc.
> H. Lonberg, P.E.,S.E.
> Principal
>
>
> -----Original Message-----
> From: TowerTalk [mailto:towertalk-bounces at contesting.com] On Behalf Of David
> Gilbert
> Sent: Sunday, September 16, 2012 8:17 PM
> To: towertalk at contesting.com
> Subject: Re: [TowerTalk] AN Wireless tower
>
>
> That's kind of a silly extrapolation, don't you think?  We're talking
> "moisture" here, not volumes of water.  What was the point of that
> comment???  As a P.E., do you seriously think that concrete is indeed not
> porous to moisture?  Why do you think that all building codes require
> treated wood for wood that is in permanent contact with concrete floors
> (i.e., plates at the bottom of frame walls)??  In case someone spills water
> on the floor?  Nope ... it's because moisture can propagate through a
> concrete slab from the ground beneath it.
>
> Dave   AB7E
>
>
>
> On 9/16/2012 6:45 PM, KR7X wrote:
>> In that case you had better tell all those concrete dams that have
>> been built that they should not be holding back those reservoirs as they
> do.
>> Regards
>> Lonberg Design Group, Ltd.
>> H. Lonberg, P.E.,S.E.
>> Principal
>>
>>
>> -----Original Message-----
>> From: TowerTalk [mailto:towertalk-bounces at contesting.com] On Behalf Of
>> David Gilbert
>> Sent: Sunday, September 16, 2012 4:20 PM
>> To: towertalk at contesting.com
>> Subject: Re: [TowerTalk] AN Wireless tower
>>
>>
>> Sorry, but that's an old wives tale.  Concrete itself is porous as
>> hell and will pass moisture almost as easily as any cinder block.
>> There is no way on this earth that concrete will keep moisture away
>> from the iron, but the alkalinity of the concrete will indeed keep the
>> iron from rusting and that's why our bridges hold together and our towers
> don't fall over.
>> 73,
>> Dave   AB7E
>>
>> p.s.  The specs for my tower called for 16 yards of concrete (9' by 9'
>> by 5' deep), but it was impossible to carve a hole with straight sides
>> into this rocky hillside so I ended up with over 20 yards myself.
>>
>>
>> On 9/16/2012 4:02 PM, Edwin Karl wrote:
>>> Do NOT use cinder blocks or red brick to support iron for the pour
>>> Use concrete material, block pieces, curb stop etc. The purpose is to
>>> keep moisture away from the iron. Cinder and red brick pass the
>>> moisture through.
>>> At least that's what we were told in the before time when I worked as
>>> an iron worker.
>>> I have an HD-90, it's a tough tower. The base got away from me and we
>>> used 22 yds of concrete. It ain't going nowhere.
>>>
>>> 73
>>> ed K0KL
>>> _______________________________________________
>>>
>>>
>>>
>>> _______________________________________________
>>> TowerTalk mailing list
>>> TowerTalk at contesting.com
>>> http://lists.contesting.com/mailman/listinfo/towertalk
>>>
>> _______________________________________________
>>
>>
>>
>> _______________________________________________
>> TowerTalk mailing list
>> TowerTalk at contesting.com
>> http://lists.contesting.com/mailman/listinfo/towertalk
>>
>> _______________________________________________
>>
>>
>>
>> _______________________________________________
>> TowerTalk mailing list
>> TowerTalk at contesting.com
>> http://lists.contesting.com/mailman/listinfo/towertalk
>>
> _______________________________________________
>
>
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk at contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
>
>