If you were Registered and logged in, you could reply and use other advanced thread options
|
Posted by ** Frank ** on October 10, 2007, 4:14 pm
Contractors and DIY use groovers or saw cut control lines so that the
concrete will break at the joints. That's the plan but more lightly the
concrete slab will crack everywhere except at the joint lines. For the
concrete slabs I saw on patios, driveways and sidewalks, it seems pointless
to have control joints. Expansion joints excepted, off course.
So the question is, when concrete cracks then how do you make it break at
the control joints more often than elsewhere?
|
| |
Posted by Malcolm Hoar on October 10, 2007, 5:51 pm
>Contractors and DIY use groovers or saw cut control lines so that the
>concrete will break at the joints. That's the plan but more lightly the
>concrete slab will crack everywhere except at the joint lines. For the
>concrete slabs I saw on patios, driveways and sidewalks, it seems pointless
>to have control joints. Expansion joints excepted, off course.
>
>So the question is, when concrete cracks then how do you make it break at
>the control joints more often than elsewhere?
It really depends on the specific situation but in general terms:
1. Prepare a proper foundation for the pour. If you pour concrete
on dirt, it'll likely crack all over the place.
2. Add steel mesh and/or rebar to each slab.
3. Use the appropriate mix and provide it with an opportunity
to cure properly (pay attention to temperature and moisture
levels).
4. Agitate and otherwise ensure a complete lack of large air
or water bubbles within the concrete itself (esp, around
any steel reinforcement).
If you do those things right, correctly sized slabs will not
crack.
--
|~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~|
| Malcolm Hoar "The more I practice, the luckier I get". |
| malch@malch.com Gary Player. |
| http://www.malch.com/ Shpx gur PQN. |
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
Posted by on October 10, 2007, 8:47 pm
On Wed, 10 Oct 2007 13:14:31 -0700, "** Frank **"
>Contractors and DIY use groovers or saw cut control lines so that the
>concrete will break at the joints. That's the plan but more lightly the
>concrete slab will crack everywhere except at the joint lines. For the
>concrete slabs I saw on patios, driveways and sidewalks, it seems pointless
>to have control joints. Expansion joints excepted, off course.
>
>So the question is, when concrete cracks then how do you make it break at
>the control joints more often than elsewhere?
>
>
>
If you aren't using steel the best chance is if you cut the joints
when the concrete is still green, certainly within 24 hours on a cool
day.. Stresses get relieved earlier while the concrete is still a
little elastic, but this still will not do anything if the substrate
you poured on is bad. Once it sets, if the ground shifts, the concrete
cracks. Steel will tend to pull that stress to a controil joint but
YMMV.
|
|
Posted by BobK207 on October 10, 2007, 9:43 pm
> Contractors and DIY use groovers or saw cut control lines so that the
> concrete will break at the joints. That's the plan but more lightly the
> concrete slab will crack everywhere except at the joint lines. For the
> concrete slabs I saw on patios, driveways and sidewalks, it seems pointless
> to have control joints. Expansion joints excepted, off course.
>
> So the question is, when concrete cracks then how do you make it break at
> the control joints more often than elsewhere?
Depends the slab thickness but for a 5" slab......place cuts such that
you have 150 sq ft max panel size (try to keep the panels somewhat
squarish) & cut depth 1/4 to 1/3 of slab thickness, cut as soon as
concrete can be worked upon without damaging surface.
Too much water in the mix can cause shrinkage cracks that cuts will
not totally help avoid.
This should work out pretty well.
cheers
Bob
|
|
Posted by DanG on October 10, 2007, 9:50 pm
I don't know that I agree with Malcolm.
Good subgrade prep and compaction - yes. Nothing wrong with the
right kind of dirt, select fill preferred. No sod, no loam,
Mesh does not reinforce concrete.
Rebar in a 4" slab does not help, actually hurts.
Avoid re-entrant corners.
Concrete wants to be square, not rectangular.
Never exceed 12' in any direction without at least a contraction
joint, closer preferred.
Cut all contraction joints a minimum of T/4, that is, 1/4 or more
of the slab thickness. Most lumberyard jointers cut 1/4" deep.
Make sure the keel is at least 1" or you're wasting your time, I
prefer 1 1/2. If the contraction joints are sawed into the slab
(my preference) they must be sawed the same day as the pour as
soon as the concrete doesn't ravel under the blade. You CANNOT
wait and cut them the next day.
Curing the concrete is crucial. If you use a curing compound,
make sure it is compatible with potential floor
finishes/adhesives. A 3 day minimum full wet cure is the best.
--
______________________________
Keep the whole world singing . . . .
DanG (remove the sevens)
dgriff237@7cox.net
> Contractors and DIY use groovers or saw cut control lines so
> that the concrete will break at the joints. That's the plan but
> more lightly the concrete slab will crack everywhere except at
> the joint lines. For the concrete slabs I saw on patios,
> driveways and sidewalks, it seems pointless to have control
> joints. Expansion joints excepted, off course.
>
> So the question is, when concrete cracks then how do you make it
> break at the control joints more often than elsewhere?
>
>
>
>
|
Page 1 of 2 1 2 > last >>
| Similar Threads | Posted | | How to cut control joints | June 29, 2006, 12:48 am |
| Concrete expansion joints | August 12, 2005, 8:16 pm |
| concrete contraction joints | December 13, 2006, 12:02 pm |
| replace expansion joints in concrete | January 3, 2006, 1:04 am |
| Filling concrete joints with cement | July 14, 2007, 10:19 am |
| Questions on joints for 4" concrete slab | March 3, 2008, 9:17 am |
| Repairing concrete driveway expansion joints | July 10, 2005, 8:38 pm |
| concrete job lacking expansion joints against foundation | August 12, 2005, 5:29 pm |
| Filling in concrete driveway expansion joints | September 21, 2005, 1:36 am |
| Deck-o-joint expansion joints and acid-etched concrete | October 7, 2006, 11:33 pm |
|
|
Yahoo! 
Google 
Windows Live 
del.icio.us 
digg 
Netscape 
XML Sitemap