[TowerTalk] Using old concrete in new pour

Jim Lux jimlux at earthlink.net
Thu Oct 23 10:13:23 EDT 2014


On 10/23/14, 6:01 AM, Brian Amos wrote:
> I would ask your friend where he got his civil engineering degree. I would
> be interested to know. Bad, bad, bad idea, unless you know what you are
> doing (he doesn't).

One doesn't need a degree to know that this is a bad idea.  And not just 
because it violates the "do what the plans say" rule (aka LXC prime 
directive)

The education would allow you to do:
1) know *why* it's a bad idea
2) potentially turn a bad idea into a good idea, with some extra work 
(as you outlined later)
3) explain why one person doing it once might get lucky, but that 
doesn't mean you should do it. anecdote is not data.


As far as grinding and reusing, I drive by a freeway rebuild every day 
and they are grinding up the old concrete to make new roadbed and 
aggregate for the new concrete alongside the road.  From a very, very 
casual inspection of the equipment (traffic doesn't move that fast 
sometimes, so you can watch the processing at your leisure), it looks 
like they're turning it into 1" or so gravel as well as a pile that is 
much finer.  I was wondering whether this grinding, sifting, and grading 
process is actually making chunks of concrete, or more about reclaiming 
the original aggregate gravel, after removing the cement matrix around it.

In this particular case, I haven't seen them making the concrete from 
the piles (although I'm sure they do, I've seen it on other projects, 
other freeways), but a lot of what that huge pile of "gravel" is used 
for is the substrate underneath the new concrete, and I suspect that the 
requirements for that material may not be as stringent as for the 
aggregate going into the concrete for the actual road.


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