JC:
I believe there is a liquid product that is applied to the first-poured
concrete that will enhance adhesion to the later pours. I can't recall it's
name; maybe someone else on the reflector knows?
However, this pier and pad foundation is a common design for cellular
tower legs (one foundation PER LEG!) So there is obviously some solution
(answer) to this problem. Also, I'd recommend using a concrete vibrator on
the second pour to ensure that the new concrete contacts all of the first
pour surface.
I didn't have to get under the undercut while either digging or placing
rebar. I was able to do both from the <safety> of the larger excavation.
But this risk is certainly something that must be carefully considered.
BTW: I looked for you guys on Sunday around 14.160 but there were too
may Q's going on and I couldn't spend much time listening (headed out to
church.) Maybe next Sunday.
73 de
Gene Smar AD3F
----- Original Message -----
From: "JC Smith" <jc-smith@comcast.net>
To: <ersmar@comcast.net>; "'Kelly Johnson'" <n6kj.kelly@gmail.com>;
<towertalk@contesting.com>
Sent: Tuesday, July 05, 2005 3:13 PM
Subject: Re: [TowerTalk] Pad and Pier Foundations
> Hi Gene,
>
> As you know, I'm planning on this type of tower. I've been looking at the
> foundation options and I really don't want a 9' x 9' (or even an 8' x 8')
> concrete pad under the tower (the Solid Block option) but I don't like the
> idea of forming and compacting either. Seems to me that if you do two
pours
> you will have a cold joint between the pad and the pier. Moisture would
> eventually get in there and rust the rebar (which is where most of your
> strength is... or all of your strength with a cold joint) and at some
point
> you would have a weakened foundation. I suppose it would take a long
time,
> and there are rebar coatings to mitigate this, but it seems to me a
> monolithic pour would be better. It would seem that a variation of the
> Drill and Bell that Rick posted might be an answer. You could still dig
the
> 5' x 5' hole with a backhoe and then dig the "square bell" pad section by
> hand or with the aid of some yet-to-be-determined mechanical device.
You'd
> still have to build the rebar cage inside the hole and to the same
> specification but at least you'd have some clearance to work with when
tying
> the rebar. I really can't see lying on my back in the hole while working
> under the ledge of the undercut tying rebar. It would be hard enough with
a
> sloped, bell X-section. It would take more concrete, but so what, and not
> as much as with the Solid Block.
>
> If one is going to go with two pours then I heartily agree with you that
> digging out enough that you can fit a mechanical tamper is the way to go.
I
> recently did my own underground utility conversion (beneath a new driveway
> we subsequently installed) and the compactor we rented was worth its
weight
> in gold. We used the type that looked like hand truck with a gas engine
on
> it (or a square lawn mower with no wheels) and backfilled about 6" at a
> time, watering the fill as we went. We purchased fill (sort of a crushed
> rock mixture) rather than try to use the clay we dug out of the trench. I
> think the width of the footprint of the tamper was about 18", but of
course
> you'd have to dig out enough to be able to turn the corners. I believe
> there are other types of compacters as well. They look sort of like a
> jackhammer with a big foot where the bit should be. They wouldn't be any
> fun to use on a long trench (ours was well over 100 yards) but on a 6' x
6'
> rectangle they might not be that bad.
>
> As was suggested by others on here, I plan to post photographs of the
entire
> process in my Photo Bucket as it happens, so anyone interested will get to
> see the whole thing. Someone suggested a video. I think a time-lapse
video
> would be really neat, but I'm not sure I'll be able to pull that off.
>
> Missed you on Sunday BTW.
>
> 73 - JC, k0hps@amsat.org
>
>
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|