[TowerTalk] Rebar Cage Question

[Donald Chester]

> I think the main thing to remember is that the purpose of the welding or 
> wire for that matter is to keep the rebar cage in tact until it has been 
> covered in concrete. Once the concrete cures, it makes NO difference. I 
> welded a few cages myself and if you can weld, this is no big deal. If 
> you cannot weld, buy a roll binding wire and get it over with.
> 
> Either way, as long as you cage can be kept in tact until you done the 
> pour, you are OK
 
> de KR5DX
 
That's pretty much my take on it.  I built mine almost 30 years ago, and tack welded the rebar together using a homebuilt arc welder.  I don't see how that would weaken the rebar, since it didn't thoroughly heat both the entire joined pieces to a glow in order to solidly weld across the entire diameter of the bar, but just enough to keep it together until the concrete was poured, much in the manner of spot welding.  I first tried wiring it together, but never could make it stable enough to my satisfaction.  

I have built reinforced concrete foundation piers under my house, where I didn't even bother to tie the rebar together at all, but simply submerged pieces of bar into the concrete, poured in some more, laid more rebar, and then finished filling in the hole or the form.  The rebar won't sink to the bottom in concrete the way it will in water, but will remain suspended exactly where you place it if it doesn't get bumped aside.  The main thing to watch out for is to make sure that all the  rebar is thoroughly covered with concrete.  You don't want any steel sticking out through the concrete in direct contact with the soil, since that may set up electrolysis and cause the steel to rust or corrode.  If that happens, the rusting rebar may actually expand enough to crack the concrete.

I don't plan to build any new towers any time soon.  I was curious about this as the result of an over-the-air discussion with another ham whose tower is still in the planning stage.  I told him that I tack welded mine together, but that some experts claim you should use wire.

I suspended my cages in the hole, using steel wire and a temporary supporting stucture while the concrete was being poured, paying close attention to the placement as the concrete went in.  Once the concrete was poured, I used wire cutters to clip off the support wires an inch or two below the surface of the concrete, to assure that all the steel was completely covered.

The tower is still up and giving good service after nearly 3 decades, so I must have done somethig right.

Don k4kyv
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