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). Doing this could likely turn 4000 psi concrete into
2000 psi concrete or worse. Each individual part of the mix is calculated
based on an amount per yard. You probably need around 6 bags (94 lbs) of
Portland cement and then a certain amount of water per yard to meet the
water-cement ratio. If using ready-mix then the dry ingredient quantities
are already done for you and you add water and go. If ready mix from a
batch plant you don't even mess with that. Some bigger projects use the
crushed concrete as part of the aggregate (as a cost saving measure) but it
still has to meet the gradation and other requirements for the aggregate
portion of the mix. If you want to do that I would say its possible but you
will have to batch the concrete onsite and you will want a good materials
testing company to get involved. Once you do that then it starts getting
expensive for a small project. Much more so than buying the extra yard of
mud from the batch plant. While prices vary across the country, here in
southern Utah we are paying about 100 bucks a yard delivered if the pour is
within 25 miles or so of a batch plant. And then there is a surcharge on
top of that for additional mileage. If I buy ready mix from home depot I
will pay about 90 bucks for a yard and then I have to mix it. Not mixing 5+
yards by hand in a wheel barrow is worth that 50 bucks to me, considering a
wheel barrow holds about 1/9 of a yard. Mud is cheap, it is the steel and
labor that isn't cheap. Sometimes "saving" a bit of money isn't worth the
extra costs of time and sore muscles. Just 2 cents from someone with an
expensive degree in civil engineering, who understands how and why concrete
works and how changing it will affect the overall product. Its not worth
saving a few bucks when you will have to redo it all down the road. Some
have talked about lawyers changing things. They dont. They get involved
when someone tries to make an extra buck by cutting corners. Don't cut
corners and don't hire people who do and you shouldn't need a lawyer.
Brian Amos, PE
KF7OVD
On Oct 21, 2014 5:53 PM, "David Gallatin via TowerTalk" <
towertalk@contesting.com> wrote:
> Hello everyone,
> A ham friend today suggested using concrete from an old pad that's broken
> into small (maybe fist size or a bit smaller) pieces and using it in
> a new pour, specifically for my new 30 foot aluminum tower. He said you
> make the new mix "a little soupy" and toss the old chunks in as you go, the
> idea being less new concrete is used (and paid for) and when it dries you
> can't tell a difference "concrete being concrete". He did not specify what
> kind of ratio of old to new is used but he does have two pads of his own he
> has done this with that hold 60' steel self supporting towers.
> I have tried to research this and come up with nothing. I did find
> reference to concrete being recycled (crushed) into aggregate size and used
> as such in new pours but what he is talking about does not seem to be the
> same thing.
>
> Obviously I am a tad concerned about doing this. Has anyone heard of this
> technique before?
>
> 73,
> David, AA9G
>
> ex W5DCG and KC9EEV
> _______________________________________________
>
>
>
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