"Robert Allison" wrote in message
news:fkPtj.36007$we5.12736@trnddc02...
MiamiCuse wrote:

I have a trench about 4; wide and 10' long in my slab that was opened up
for plumbing drain relocation and now I am ready to close it up. I will
put the sand back in and compact it real well, then termicide, then
moisture barrier, then I plan to add dowels to both sides of the existing
slab and pour new concrete.

It is very difficult to do the dowels because the trench width it
irregular. As I did the first two I started to think if I position the
dowels differently would it make the job easier and actually more
effective?

Instead of drilling holes on existing edges, why put the end of the dowel
at the bottom of one slab, then pound it deep into the sand as far as it
will go at an incline, when the dowel is shortened to be about the same
width as the trench, start pounding it down until it wedges into the
existing concrete on the other side. So basically the dowel will bridge
the trench from below one slab to the middle of another slab, sort of
pushing up the existing slab.

If I continue this pattern, alternating the dowels say every 16 inches, I
will have an even number of dowels on each side, angled up. If I pour
concrete in and embed it into the new concrete, would it not be like
pretensioning it? Seems to me logically would hold the new concrete up
better...or am I nutz?

MC

No. Bad idea. The rebar is supposed to be protected from exposure to
earth or even air, because the most common problem for rebar is failure
due to rust. Embedding the rebar in the dirt will drastically accelerate
its deterioration due to oxidation (rust). Your rebar should be no closer
than 2" to the dirt (or at the center of the slab, vertically).

In addition, the rebar in this instance is not to strengthen the concrete,
but to tie the old concrete to the new. This is to keep the new and the
old from settling differently. You want both to act as a unit, therefore
the dowels.

To make the job easier, instead of trying to drill straight into the
concrete, drill at a 45 degree or less angle (on the horizontal axis) .
Then install your rebar and bend it straight. This allows you to get your
hammer drill into tighter spaces.

--
Robert Allison
Rimshot, Inc.
Georgetown, TX

Thanks Robert did not think about that...ok

although I think they will rust anyways. The original slab I broke has wire
meshes in the concrete and they were all rusted, the cast iron drain below
that I replaced has exterior corrosion. The water table in Miami is very
high.

Install the rebars eccentrically and bent it straight? What size rebar?

MC