A couple of notes on bases:
1; Concrete tales 30 days to reach 90% ultimate strength under average
conditions. Heat, dryness, and mix will vary this time but usually to the
longer side. The so-called high/early will reach the 65% to 80% quicker but
still take as long to reach the ultimate strength. Putting stress on concrete
too early with a tower is a sure way to develop cracking and prevent the
concrete to achieve a homogeneous mass as desired.
2: Just a layer of 4 or 6 mill plastic stapled over form boards will prevent
sticking and the plastic is available everywhere.
3: Concrete poured over undisturbed soil will give you the load bearing
capacity that the base size was based on. Any soil or added gravel must be
compacted to at least 90% of its compact-ability to be equal to undisturbed
4: The "drying" of concrete is actually a curing process. The cement in the
concrete mix is reforming the crystal formation it had as limestone before it
had all the water baked out of it in the kiln at the concrete plant. Its more
of a chemical process that yields a crystal and some heat . The heat is a enemy
of concrete curing and in larger pours must be accounted for. In the warmer
temps of summer you should never allow concrete to dry out for the first week
at least. All good companies that pour large slabs us some form of retardant on
top of slab to slow evaporation. In our context this means just keep everything
wet, the soil should be saturated (sand and gravel in bottom should be covered
with plastic) and water sprayed at regular intervals on finished concrete.
Just don't spray hard enough to erode surface.
5: I agree whole heatedly with others who have stated that compacting the
soil around base after form removal is difficult and often skimped on believing
that all will settle in somehow. I hope that no one will skip this crucial step
and that they will used some form of mechanical compaction and not just stomp
it down and call it good.
I"m sure that with all the fine information on this group we will all have
safe bases under our towers that are sprouting this summer.
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