Shattering concrete floor?

[bluechip]

He needs to break through a concrete floor in an outbuilding to sink
wooden fence posts in for a construction project. Up until now he's
been using an electric 29 kg jack hammer to break through the concrete
perfectly. However the jack hammer is gone now and there are still a
few holes to sink. He considers it a perfect opportunity to actually
do something useful with explosives that works out cheaper than hiring
the drill again for a whole day.

Anyway he needs to know what people's opinions are on how much
explosive to use and how to position it properly for the most
efficient blast.

The specs are :

AN/NM is the only medium/high velocity 'shattering' explosive he has
available.

The floor is about 2 - 3 inches of non reinforced conrete poured onto
about a foot of semi compacted hardcore of various sizes. This is
sitting on dry clay.

He needs to simply shatter the concrete over about a 12 inch diameter
circle. This is what he was doing with the drill and it was a
relatively simple matter afterwards to dig the shattered bits out and
dig through the hardcore.

He plans to simply contain the AN/NM charge in a ziplock bag, place
the charge on the floor and tamp it from above with a heavy, wet
sandbag.

So how much will he need to use to shatter the concrete? And is his
thinking on the placement and containment correct? Obviously he wants
to minimise the noise and use as little explosive material as he can.

Note - there is no way to drill into the floor as the equipment isn't
available - the charges must be placed onto the floor. Also, anything
involving shaped charges is too overkill/time consuming/advanced. He'd
be better just getting the jack hammer back.

Thanks in advance
bluechip

[Edward Hennessey]

Explosives aren't the way to accomplish your friend's goal, unless his
aim is to have a wayward pretext for using explosives.

Go rent a cut-off saw with a gasoline engine and a diamond blade with
a wet kit to both cool the blade and keep the rock dust from becoming
airborne.
Saw out your holes. Dig out your footings to a sufficient dept for
heavy-duty
4"x4" or 8"x8" metal brackets for mounting posts. I would dig a hole at
least 18"
deep and 14" square depending on what you are going to construct on the
posts.
By the way, 2"-3" of unreinforced concrete as a floor slab is just a bit
substandard for anything but the lightest loads and traffic, especially if
temperature complications
are a factor. Overbuilding is less consequential and amusing than skimping
on your work: decide whether you want to invest a bit more effort initially
or have a lot
more laughs and rework later.

Put a few inches of broken rock or gravel at the bottom of your hole.
Lightly roughen
and clean your cut, moisten your hole, apply concrete adhesive to the
slab and make your pour. If you are thinking about laying concrete in frozen
conditions, think how
much easier and wiser it would be to work when the birds are back to
serenade you When your
pour starts to set sufficiently, put in your metal post anchors. Plumb and
level the anchors. Keep the
concrete moist using saturated rags for a period of 2 weeks if you want it
to reach the practical
maximum strength. You can bolt your posts in as early as 7 days after laying
your concrete but
waiting until the concrete has cured more is better.

Putting wood into direct contact with concrete invites deterioration and the
eventual necessity
of breaking up your work and doing everything over again. Once you have your
posts bolted into
their metal anchors, all you need to do is keep things painted and tight. If
a post becomes compromised,
unbolt and replace it...quick and simple.

Bagged charges on concrete will shatter it all right. How you are going to
get contained, precision shattering
in the thin slab might merit consideration along with things like flyrock,
filth, noise, legality and safety,etcetera.
Concrete saws are readily available and unless there are a forest of posts
to install, you should
be able to do what you need rapidly, safely and accurately. If your aims are
otherwise, explosives would
be an option.

Regards,

Edward Hennessey

Post by bluechip
He needs to break through a concrete floor in an outbuilding to sink
wooden fence posts in for a construction project. Up until now he's
been using an electric 29 kg jack hammer to break through the concrete
perfectly. However the jack hammer is gone now and there are still a
few holes to sink. He considers it a perfect opportunity to actually
do something useful with explosives that works out cheaper than hiring
the drill again for a whole day.
Anyway he needs to know what people's opinions are on how much
explosive to use and how to position it properly for the most
efficient blast.
AN/NM is the only medium/high velocity 'shattering' explosive he has
available.
The floor is about 2 - 3 inches of non reinforced conrete poured onto
about a foot of semi compacted hardcore of various sizes. This is
sitting on dry clay.
He needs to simply shatter the concrete over about a 12 inch diameter
circle. This is what he was doing with the drill and it was a
relatively simple matter afterwards to dig the shattered bits out and
dig through the hardcore.
He plans to simply contain the AN/NM charge in a ziplock bag, place
the charge on the floor and tamp it from above with a heavy, wet
sandbag.
So how much will he need to use to shatter the concrete? And is his
thinking on the placement and containment correct? Obviously he wants
to minimise the noise and use as little explosive material as he can.
Note - there is no way to drill into the floor as the equipment isn't
available - the charges must be placed onto the floor. Also, anything
involving shaped charges is too overkill/time consuming/advanced. He'd
be better just getting the jack hammer back.
Thanks in advance
bluechip

[Richard Casady]

On Wed, 17 Dec 2003 21:54:19 GMT, "Edward Hennessey"

Post by Edward Hennessey
Explosives aren't the way to accomplish your friend's goal, unless his
aim is to have a wayward pretext for using explosives.
Go rent a cut-off saw with a gasoline engine and a diamond blade with
a wet kit to both cool the blade and keep the rock dust from becoming
airborne.
Saw out your holes. Dig out your footings to a sufficient dept for
heavy-duty
4"x4" or 8"x8" metal brackets for mounting posts. I would dig a hole at
least 18"
deep and 14" square depending on what you are going to construct on the
posts.
By the way, 2"-3" of unreinforced concrete as a floor slab is just a bit
substandard for anything but the lightest loads and traffic, especially if
temperature complications
are a factor. Overbuilding is less consequential and amusing than skimping
on your work: decide whether you want to invest a bit more effort initially
or have a lot
more laughs and rework later.
Put a few inches of broken rock or gravel at the bottom of your hole.
Lightly roughen
and clean your cut, moisten your hole, apply concrete adhesive to the
slab and make your pour. If you are thinking about laying concrete in frozen
conditions, think how
much easier and wiser it would be to work when the birds are back to
serenade you When your
pour starts to set sufficiently, put in your metal post anchors. Plumb and
level the anchors. Keep the
concrete moist using saturated rags for a period of 2 weeks if you want it
to reach the practical
maximum strength. You can bolt your posts in as early as 7 days after laying
your concrete but
waiting until the concrete has cured more is better.
Putting wood into direct contact with concrete invites deterioration and the
eventual necessity
of breaking up your work and doing everything over again. Once you have your
posts bolted into
their metal anchors, all you need to do is keep things painted and tight. If
a post becomes compromised,
unbolt and replace it...quick and simple.
Bagged charges on concrete will shatter it all right. How you are going to
get contained, precision shattering
in the thin slab might merit consideration along with things like flyrock,
filth, noise, legality and safety,etcetera.
Concrete saws are readily available and unless there are a forest of posts
to install, you should
be able to do what you need rapidly, safely and accurately. If your aims are
otherwise, explosives would
be an option.
Regards,
Edward Hennessey

Post by bluechip
He needs to break through a concrete floor in an outbuilding to sink
wooden fence posts in for a construction project. Up until now he's
been using an electric 29 kg jack hammer to break through the concrete
perfectly. However the jack hammer is gone now and there are still a
few holes to sink. He considers it a perfect opportunity to actually
do something useful with explosives that works out cheaper than hiring
the drill again for a whole day.
Anyway he needs to know what people's opinions are on how much
explosive to use and how to position it properly for the most
efficient blast.
AN/NM is the only medium/high velocity 'shattering' explosive he has
available.
The floor is about 2 - 3 inches of non reinforced conrete poured onto
about a foot of semi compacted hardcore of various sizes. This is
sitting on dry clay.
He needs to simply shatter the concrete over about a 12 inch diameter
circle. This is what he was doing with the drill and it was a
relatively simple matter afterwards to dig the shattered bits out and
dig through the hardcore.
He plans to simply contain the AN/NM charge in a ziplock bag, place
the charge on the floor and tamp it from above with a heavy, wet
sandbag.
So how much will he need to use to shatter the concrete? And is his
thinking on the placement and containment correct? Obviously he wants
to minimise the noise and use as little explosive material as he can.
Note - there is no way to drill into the floor as the equipment isn't
available - the charges must be placed onto the floor. Also, anything
involving shaped charges is too overkill/time consuming/advanced. He'd
be better just getting the jack hammer back.

Use the jackhammer.[ At one time it was JackHammer[TM] for Ingersoll
Rand's 90 pound vertical drilling hammer, but whatever]. on the other
hand, it is harder to fish with a drill.

Casady