On Feb 16, 9:09 pm, Robert Allison wrote:
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

MC-

Robert hit all the important points....follow his advice & your slab
will easily outlast you.

Don't & the slab will fail in a few years.

A variable speed rotary hammer will make drilling easier.

cheers
Bob