Concrete cracks either because of settling or shifting in the earth
below from the time when the concrete mix was originally laid

Read mo How to Mend Cracks in Concrete | eHow.com
http://www.ehow.com/how_7195102_mend...#ixzz2RbnjwWG7

Is there a way to tell if the cracks are caused by geology or if the
driveway was not properly packed before the concrete?

The tennis courts at our recreation department also have some pretty
significant cracks.
----------
entropy sucks

On Fri, 26 Apr 2013 17:57:04 -0400, Metspitzer
wrote:

Concrete cracks either because of settling or shifting in the earth
below from the time when the concrete mix was originally laid

Read mo How to Mend Cracks in Concrete | eHow.com
http://www.ehow.com/how_7195102_mend...#ixzz2RbnjwWG7

Is there a way to tell if the cracks are caused by geology or if the
driveway was not properly packed before the concrete?

The tennis courts at our recreation department also have some pretty
significant cracks.
----------
entropy sucks

Average concrete that has no joints is going to crack roughly every 15
feet due to normal shrinkage. How wide are the tennis court slabs
between construction joints?

Metspitzer wrote in
:

Concrete cracks either because of settling or shifting in the earth
below from the time when the concrete mix was originally laid

Read mo How to Mend Cracks in Concrete | eHow.com
http://www.ehow.com/how_7195102_mend...#ixzz2RbnjwWG7

Is there a way to tell if the cracks are caused by geology or if the
driveway was not properly packed before the concrete?



It's probably both. Plus poor drainage.

Most of the time driveway cracks are caused by poor bed-preparation, often
combined with poor drainage (who has ditches on either side of his
driveway?).

Residential driveways basically consist of whatever ground the home-
building equipment drove over while the house was built, plus a couple of
inches of gravel spread around afterwards. And the lawn will be level with
the pavement.

Nobody builds a driveway the way a road is built -- unless he works in
road-construction, and takes two months to prep and build his driveway
(I've seen this done, many times!).



The tennis courts at our recreation department also have some pretty
significant cracks.



Poor drainage and/or poor bed-prep. What's the drainage like? Drainage is
probably more important than bed-prep.



----------
entropy sucks



Mine increases as the week goes on. Always.



--
Tegger

On Sat, 27 Apr 2013 00:09:41 +0000 (UTC), Tegger
wrote:

Metspitzer wrote in
:

Concrete cracks either because of settling or shifting in the earth
below from the time when the concrete mix was originally laid

Read mo How to Mend Cracks in Concrete | eHow.com
http://www.ehow.com/how_7195102_mend...#ixzz2RbnjwWG7

Is there a way to tell if the cracks are caused by geology or if the
driveway was not properly packed before the concrete?



It's probably both. Plus poor drainage.

Most of the time driveway cracks are caused by poor bed-preparation, often
combined with poor drainage (who has ditches on either side of his
driveway?).

Residential driveways basically consist of whatever ground the home-
building equipment drove over while the house was built, plus a couple of
inches of gravel spread around afterwards. And the lawn will be level with
the pavement.

Nobody builds a driveway the way a road is built -- unless he works in
road-construction, and takes two months to prep and build his driveway
(I've seen this done, many times!).



The tennis courts at our recreation department also have some pretty
significant cracks.



Poor drainage and/or poor bed-prep. What's the drainage like? Drainage is
probably more important than bed-prep.


Lets not forget that in many cases the concrete that is supplied is
crap, far far below the quality that would be used in any commercial
project.

If I were building a driveway, I would pour it 8 inches thick instead of 6 or 4 and put two layers of rebar in; one an inch below the top of the slab and the other an inch above the bottom of the slab.

The reason why drywall is as strong and rigid as it is (considering what it's made of) is because paper is very strong in tension. Try folding up a sheet of paper so that it's 11 1/2 inches long an 1 inch wide and pulling it apart by straight tension (rather than by tearing it) and you'll see how strong paper actually is.

In order for drywall to bend, the paper on one side of the gypsum or the other has to stretch to conform to the new shape, and it's the strenth of the paper on each side of the drywall and it's resistance to stretching that gives drywall it's strength and rigidity.

Reinforced concrete is designed exactly the same way. "Reinforced" concrete consists of ordinary concrete with rebar inside it. If you imagine a slab of concrete with two layers of rebar inside the concrete; one near the top of the concrete and one near the bottom, then for that slab to bend, the rebar on either side would have to stretch to conform to the new shape.

But, since steel is very strong in tension, it's the steel's resistance to stretching that would prevents the slab from bending, and therefore cracking. That is, the slab could support very much MORE weight or force on it before it bent far enough for the concrete to crack. The steel rebar carries the load so that the reinforced concrete slab DOESN'T bend far enough for the concrete to crack, and that's why reinforced concrete is so much stronger than unreinforced concrete. It's exactly the same reason why drywall is considerably stronger than the gypsum core itself.

The problem is that when they pour a typical garage pad or drive way, THEY DON'T put the rebar where it's needed, which is at the top and bottom surfaces of the slab so it's in the proper location to resist bending of the slab. Instead, they just put a layer of rebar in the MIDDLE of the slab; equidistant from the top and bottom of the slab where it's unable to prevent the slab from bending. So, the slab bends easily to the point where the concrete cracks, and for $50 more for a second layer of rebar and $100 more in labour to install that second layer of rebar before pouring the concrete, you could have prevented that driveway slab from cracking.

Really, when they put a layer of rebar in the middle of a slab, the purpose is NOT to strengthen the concrete like it would if you had two layers. The purpose of that single layer of rebar in the middle of the slab is simply to hold the pieces of slab together AFTER it cracks. The idea is just to prevent any cracks from spreading. TWO layers of rebar would also prevent any cracks from spreading, but two layers properly located would go a far sight further to prevent the slab from cracking in the first place.

If you made drywall the same way they pour your average driveway, what you'd have is a layer of paper sandwiched between two 1/4 inch thick layers of gypsum. Something like that is gonna break if you breathe on it too hard. Putting the paper on the outsides makes the drywall strong and rigid because it takes a lot of force to stretch paper. Ditto for steel, and putting steel on the outsides of a concrete slab would make for a very much stronger and more rigid slab of concrete; one much less likely to bend to the point where it cracks.

On Apr 27, 2:28*am, nestork wrote:
If I were building a driveway, I would pour it 8 inches thick instead of


The problem is that when they pour a typical garage pad or drive way,
THEY DON'T put the rebar where it's needed, which is at the top and
bottom surfaces of the slab so it's in the proper location to resist
bending of the slab. *Instead, they just put a layer of rebar in the
MIDDLE of the slab; equidistant from the top and bottom of the slab
where it's unable to prevent the slab from bending. *So, the slab bends
easily to the point where the concrete cracks, and for $50 more for a
second layer of rebar and $100 more in labour to install that second
layer of rebar before pouring the concrete, you could have prevented
that driveway slab from cracking.

Really, when they put a layer of rebar in the middle of a slab, the
purpose is NOT to strengthen the concrete like it would if you had two
layers. *The purpose of that single layer of rebar in the middle of the
slab is simply to hold the pieces of slab together AFTER it cracks. *The
idea is just to prevent any cracks from spreading. *TWO layers of rebar
would also prevent any cracks from spreading, but two layers properly
located would go a far sight further to prevent the slab from cracking
in the first place.

If you made drywall the same way they pour your average driveway, what
you'd have is a layer of paper sandwiched between two 1/4 inch thick
layers of gypsum. *Something like that is gonna break if you breathe on
it too hard. *Putting the paper on the outsides makes the drywall strong
and rigid because it takes a lot of force to stretch paper. *Ditto for
steel, and putting steel on the outsides of a concrete slab would make
for a very much stronger and more rigid slab of concrete; one much less
likely to bend to the point where it cracks.

--
nestork

The above is true.
Plus expansion/movement joints at intervals.
Easiest to put in when the job is finished with a diamond disk cutter.
It only takes one delivery truck on your driveway to crack it.

On Sat, 27 Apr 2013 03:28:14 +0200, nestork
wrote:


If I were building a driveway, I would pour it 8 inches thick instead of
6 or 4 and put two layers of rebar in; one an inch below the top of the
slab and the other an inch above the bottom of the slab.


If I were using 8" thick concrete for a driveway I would not put any
rebar in it. You don't need it unless you are planning on landing
commercial jet aircraft and the rebar will eventually corrode and
crack the concrete. Just saw joints every 12 feet about 12 hours
after it's poured.

On Sat, 27 Apr 2013 01:22:06 -0700, Ashton Crusher
wrote:

On Sat, 27 Apr 2013 03:28:14 +0200, nestork
wrote:


If I were building a driveway, I would pour it 8 inches thick instead of
6 or 4 and put two layers of rebar in; one an inch below the top of the
slab and the other an inch above the bottom of the slab.


If I were using 8" thick concrete for a driveway I would not put any
rebar in it. You don't need it unless you are planning on landing
commercial jet aircraft and the rebar will eventually corrode and
crack the concrete. Just saw joints every 12 feet about 12 hours
after it's poured.

If it were me, I'd still put some rebar in it just for any possible
flexure or tension. Besides, the cost of rebar is minimal when added
to concrete costs.

On Apr 27, 7:09*am, "Doug" wrote:
On Sat, 27 Apr 2013 01:22:06 -0700, Ashton Crusher
wrote:

On Sat, 27 Apr 2013 03:28:14 +0200, nestork
wrote:

If I were building a driveway, I would pour it 8 inches thick instead of
6 or 4 and put two layers of rebar in; one an inch below the top of the
slab and the other an inch above the bottom of the slab.

If I were using 8" thick concrete for a driveway I would not put any
rebar in it. *You don't need it unless you are planning on landing
commercial jet aircraft and the rebar will eventually corrode and
crack the concrete. *Just saw joints every 12 feet about 12 hours
after it's poured.

If it were me, I'd still put some rebar in it just for any possible
flexure or tension. *Besides, the cost of rebar is minimal when added
to concrete costs.

interstate hiwghways are built with multiple layers, gravel bed well
drained, a 6 inch concrete surface, that will never be driven on, then
more gravel etc, then the 12 inch or so finished driving surface, with
rebar.

for driveways this is expensive overkill.

even interstates crack......

Metspitzer wrote:

Read mo How to Mend Cracks in Concrete | eHow.com
http://www.ehow.com/how_7195102_mend...#ixzz2RbnjwWG7

Read more intelligently:
http://www.concretenetwork.com/concr...ys/basics.html
quote headings
A properly prepared subgrade
The correct concrete mix
Correctly placed joints
Reinforcement
Placing concrete at the proper thickness
Proper finishing
Proper drainage
Proper curing techniques
/q

Is there a way to tell if the cracks are caused by geology or if the
driveway was not properly packed before the concrete?

Yes (see above)

Additional reading: Concrete basics and more ("Outer view of the Roman Pantheon, still the largest unreinforced solid concrete dome."):
http://en.wikipedia.org/wiki/Concrete


Susan

On Sat, 27 Apr 2013 01:22:06 -0700, Ashton Crusher
wrote:

On Sat, 27 Apr 2013 03:28:14 +0200, nestork
wrote:


If I were building a driveway, I would pour it 8 inches thick instead of
6 or 4 and put two layers of rebar in; one an inch below the top of the
slab and the other an inch above the bottom of the slab.


If I were using 8" thick concrete for a driveway I would not put any
rebar in it. You don't need it unless you are planning on landing
commercial jet aircraft and the rebar will eventually corrode and
crack the concrete. Just saw joints every 12 feet about 12 hours
after it's poured.

When the mix is ordered, it can be ordered in PSI (pressure sq. inch).
Higher is better for a slab.

On Sat, 27 Apr 2013 04:28:17 -0700 (PDT), bob haller
wrote:

On Apr 27, 7:09*am, "Doug" wrote:
On Sat, 27 Apr 2013 01:22:06 -0700, Ashton Crusher
wrote:

On Sat, 27 Apr 2013 03:28:14 +0200, nestork
wrote:

If I were building a driveway, I would pour it 8 inches thick instead of
6 or 4 and put two layers of rebar in; one an inch below the top of the
slab and the other an inch above the bottom of the slab.

If I were using 8" thick concrete for a driveway I would not put any
rebar in it. *You don't need it unless you are planning on landing
commercial jet aircraft and the rebar will eventually corrode and
crack the concrete. *Just saw joints every 12 feet about 12 hours
after it's poured.

If it were me, I'd still put some rebar in it just for any possible
flexure or tension. *Besides, the cost of rebar is minimal when added
to concrete costs.

interstate hiwghways are built with multiple layers, gravel bed well
drained, a 6 inch concrete surface, that will never be driven on, then
more gravel etc, then the 12 inch or so finished driving surface, with
rebar.

for driveways this is expensive overkill.

even interstates crack......

You are correct of course but I'd still use some rebar if it were me.
Actually I might use steel wire mesh instead if the rebar doesn't have
enough cover. Overkill probably but I'd do it.

As a side note that agrees with you from many years ago....... my dad
was a builder / carpenter and when I was young he poured a long
driveway with no rebar except near the end of the driveway where it
met the street and from the driveway connecting on an incline to the
garage slab. This driveway was built upon Long Island sand and per
Google Maps, I can still see the driveway slab exist today g.

"nestork" wrote in message
...

If I were building a driveway, I would pour it 8 inches thick instead of
6 or 4 and put two layers of rebar in; one an inch below the top of the
slab and the other an inch above the bottom of the slab.

Thank you for the laugh.


Reinforced concrete is designed exactly the same way. "Reinforced"
concrete consists of ordinary concrete with rebar inside it. If you
imagine a slab of concrete with two layers of rebar inside the concrete;
one near the top of the concrete and one near the bottom, then for that
slab to bend, the rebar on either side would have to stretch to conform
to the new shape.

There is no such thing as "ordinary" concrete. Concrete is specified or
"spec'd".

The problem is that when they pour a typical garage pad or drive way,

Concrete is never poured, it is placed.


Really, when they put a layer of rebar in the middle of a slab, the
purpose is NOT to strengthen the concrete like it would if you had two
layers. The purpose of that single layer of rebar in the middle of the
slab is simply to hold the pieces of slab together AFTER it cracks. The
idea is just to prevent any cracks from spreading. TWO layers of rebar
would also prevent any cracks from spreading, but two layers properly
located would go a far sight further to prevent the slab from cracking
in the first place.


Relief/control joints are made to "crack". You are only partially correct
about single sticks of rebar. You are absolutely wrong about your
hypothetical reasoning.

Where in the heck did you get your ideas from?

I got them pounded into my head at the University of Manitoba,
specifically, the Dept. of Mechanical Engineering.
http://umanitoba.ca/faculties/engine...ts/mechanical/

And they're not my ideas.
They're engineering principles.

Or, do you figure that whomever designed the first I-beam



was just stealing my ideas?

Notice that for an I-beam to bend, then the top or bottom flange has to stretch.

And notice that, everything else being equal, a beam with an "I" cross sectional shape is harder to bend than a beam with an "O" cross sectional shape:



(Harder to bend in the direction that would cause the top or bottom flange of the I-beam to stretch, that is.)

And that's because in the case of the I-beam, more steel has to stretch for the I-beam to bend. That makes it "harder to bend".

If they were my ideas, I'd have already patented steel I beams and drywall and reinforced concrete and engineered wood joists, and I'd be rich and cruising around the Carribean on my yaucht instead of posting on this lousy stinking Home Repair newsgroup.

"nestork" wrote in message
...

Chomper;3054199 Wrote:
Where in the heck did you get your ideas from?

University of Manitoba
Dept. of Mechanical Engineering
http://umanitoba.ca/faculties/engine...ts/mechanical/

They're not my ideas.
They're common sense.

If you're trying to convince me, this is what they teach for residential
concrete placing, you can go **** up a rope. Maybe you're an unemployed
engineer, and I can understand why.

Now if you would say you were ACI certified, we may have something in
common. But then, you would have never made the ludicrous statements you
made, and I wouldn't have had the laugh that I did.

bob haller wrote:
On Apr 27, 7:09 am, "Doug" wrote:
On Sat, 27 Apr 2013 01:22:06 -0700, Ashton Crusher
wrote:

On Sat, 27 Apr 2013 03:28:14 +0200, nestork
wrote:

If I were building a driveway, I would pour it 8 inches thick instead of
6 or 4 and put two layers of rebar in; one an inch below the top of the
slab and the other an inch above the bottom of the slab.

If I were using 8" thick concrete for a driveway I would not put any
rebar in it. You don't need it unless you are planning on landing
commercial jet aircraft and the rebar will eventually corrode and
crack the concrete. Just saw joints every 12 feet about 12 hours
after it's poured.

If it were me, I'd still put some rebar in it just for any possible
flexure or tension. Besides, the cost of rebar is minimal when added
to concrete costs.

interstate hiwghways are built with multiple layers, gravel bed well
drained, a 6 inch concrete surface, that will never be driven on, then
more gravel etc, then the 12 inch or so finished driving surface, with
rebar.

for driveways this is expensive overkill.

even interstates crack......

....and when they do, I've yet to see one repaired in such a manner that I'm
not subjected to thump...thump...thump...for miles.

Most of the time they cut out a section and fill it with asphalt. It's
never level and the asphalt usually comes out after awhile leaving bigger
holes and sharper edges than the original crack.

I understand the concept of a concrete roadway lasting longer than asphalt,
but once they need repair they seem a lot worse than a repaired asphalt
roadway.

On Sun, 28 Apr 2013 06:59:51 +0200, nestork
wrote:


Chomper;3054199 Wrote:
Where in the heck did you get your ideas from?

University of Manitoba
Dept. of Mechanical Engineering
http://umanitoba.ca/faculties/engine...ts/mechanical/

They're not my ideas.
They're common sense.


Just curious where in this link? I can't speak for Canada but here
in the states, it would be under Civil / Structural Design.