Dan, in my previous tower base as well as the 3 basses I currently have & 1
planned, I used rebar cages AND the course fiber with #4000 concrete. Let me
explain why “I did it this way”
The reason I use fiber fill is to help prevent cracks and fractures in the
concrete when it cures. I also use reduced water in the mixture and exchange
20%
of the sand for pea gravel to further reduce the water required in the mix
(has to do with surface area of sand/surface area of pea gravel)……the less
water in the mix means lesser shrinkage during curing. Expansion and
contracting
in the concrete will induce cracking. HOWEVER, reduced water (less slump) means
the concrete wont “flow”. It will me harder to move around the rebar, will
reduced curing times and more difficult to finish the top.
The rebar cage is electrically bonded to the tower section planted in the
concrete with #4 solid copper in 3 places on the tower faces to the rebar
(covered in concrete). I have also tied my tower above the concrete level to
ground
rods about 16’ (2x ground rod lengths to prevent the electrical saturation of
the grounds)
The rebar cage and the concrete base is called a UFER ground (google it). Dr.
Ufer found out that concrete absorbs moisture fairly quickly and releases it
slowly. The releasing of the moisture to the sourrounding soil improves the
conductivity of the soil from electrolytes in the concrete mix. Even though the
concrete base is not a perfect conductor-it will conduct “some” of the strike
energy. My theory is if I can dissipate any portion of the strike energy, USE
IT to my advantage.
Ufer grounding is required in many local building codes per NEC. I don’t have
a NEC book with me but google “NEC UFER”…….there should be no reason to NOT
use all available sources to decrease the possible damage due to a lightning
strike…..ie air terminals, ground rods, salt wells, Ufer ground, spark gaps
on window line and open wire feeders, arrestors for coax and rotor cable
isolators.
If you ask 10 hams their opinion on the subject of grounding you will get 11
different responses (somebody will give you 2 answers). Im not saying we are
all 100% correct or we are 100% wrong…..we are just hams enjoying our hobby and
trying to give information to someone else since most of us had an elmer to
advise us at one time or another. Im not paying for your damaged equipment and
your not paying for mine…I got a few pics to send if you want to see
de david, k5qwo, el2rl, yi9qwo (ex: kd5qwo)
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