I shall be installing a base for 100' of Rohn 45 by hauling in
Portland Cement and using mostly materials found on site. This
will essentially be a CB2, a BPC45G base, and a pier pin. I am
designing do-it-yourself (DIY) concrete and will use this project
as hands-on experience from which I wish to write an article on
the subject. For reference, two other towers here were done with
ready mix.
The DIY design will be based on available materials to the extent
that I can meet or exceed standard designs. I would like to be
able to discuss what results can be expected by various
deviations from standard designs. What I'm looking for here via
TT is to build a bibliography of reference books, web sites, and
messages as a basis to write this research paper.
Here are some of my early thoughts.
1. The sand will come from the hole and elsewhere in the yard.
(I live on a historic sand bar!). A county septic system
inspector tested sand by squeezing a hand full and if a ball
results it's mud and if it falls apart it is sand. Hmmm. I'll
need to build a sluiceway to wash the sand and use a REAL test
method.
2. The stone aggregate will be of various sizes. Concrete from
old highways is pulverized and reused so I'm looking at using
pieces of crushed building block and a sidewalk along several
sizes of gravel left over other construction projects.
3. I have plenty of 8" building block. Precast concrete is a
big buzz phrase in construction. Perhaps I could build about
three courses of block, mortar them together, and build a cage in
and around them. When the mortar has cured, I could pour in and
around the block. I may need to soak the block before the final
pour so it won't blot moisture from the mix before it hydrates.
4. More about the rebar. I have more iron that Rohn specifies
consisting of rebar and iron construction frames that I can cut.
I may be able install an impressive and expensive (using free
material) metal reinforcement. I am looking for literature about
the contribution reinforcing iron to the strength and durability
of concrete.
5. The Roan catalog specifies the concrete to be four feet deep
regardless of location. The county inspector says my code
freeze depth here is 2'6". Of course, I need to get down into
undisturbed soil. Are there other depth considerations?
6. What PSI rating should the concrete have? The vertical
vector of the guys pulling the tower into the base plus the less
significant weight of the tower, equipment, and climbers come to
some 5,000 pounds. What safety multiplying factor should I
apply?
7. On a prior pour, the driver of the ready mix truck added
water based on his experience. The DIY designer lacks that
experience, so I plan on describing how to build a slump tester.
(A slump test is the measurement of the time for a cone of
concrete to slump down to a specified height.)
8. I need to find a reference about the impact, if any, of
thermo coefficients of the various materials. Will the heat from
the hydration be a problem with strange metal stuff in the
concrete? How much will prestressing help?
9. Finally, I need to learn more about keeping the concrete
moist after it has been poured for so that it can cure before it
drys. I can erect a tent over the pour to protect it from sun
and rain and allow me to mist it on schedule, whatever that
schedule is.
I look forward to receive comments from TT readers with or
without a reference source in the literature or on Internet. I'm
finding lots of civil engineering stuff on dot-EDU sites.
I'm really after a learning experience so I know that I should
hand mix. But, it's not a perfect world; I'll use a powered
mixer.
73, Dick Wilder, K3DI k3di@arrl.net
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