In article ,
Leon Fisk wrote:

Ahh... but what if you purposely built/added strategically
placed threaded rods and such. I'm sure they would have to
be somehow enclosed in a sleeve, a bit protected from the
cement mixture. After the cement has setup/cured, slap on
plates/washers over them and then add tension to provide for
cyclic operations.

Yup - that's post-tensioning, an extremely effective (and adjustable)
method for reinforcing concrete by placing it in compression. Works
great right up until some idiot decides to cut a hole in the floor and
chops though a tensioning cable (Third hand at best, but I gather it
happens occasionally)

In mulling this a bit more, one thought for dealing with differential
expansion on long embedded metal parts (ie, ways that you are "beefing
up" with concrete) is to arrange so that the part is only locked in at
one point, and is physically captured by shape (a dovetail, say) but
free to slide (even hit with some mold release wax before casting)
elsewhere.

One thing mentioned rather early in the referenced thread was effective
damping by casting epoxy granite (I think) inside innertubes or rubber
bags inside hollow section steel. While it would not add much to
strength, the simplicity of fabricating a frame from large square
section steel and then damping it by stuffing the box sections with
material might be a worthy low-end route. IIRC the rubber-encased was
better than direct cast, probably due both to damping from the rubber,
and not having the voids that will develop due to differential expansion
of direct-cast material in a steel tube - the rubber would allow for
slippage with expansion/contraction.

Then there are the granite tools which slide granite over granite on air
bearings...but those seem rather far out for DIY. What I read (I don't
claim to have read every post) of the threads at CNCzone seemed to have
a lot of churn and not much experimenting, at least not in a functional
way. The guy who's still fussing over epoxy formulations 2 years on and
has evidently never even made a test sample with aggregate is over-fussy
or something like that. The one guy participating in the thread
(Walter?) who seemed to be willing to toss some stuff in a form and see
what happened evidently gave up and moved on. AFAICT the guys in Germany
that were doing this and inspired the 2-year, 3000+ post thread have
been happily making actual stuff with the process while CNCzone has
pondered its perfection at length...but I could have missed something.

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