Create joints on existing jointless concrete driveway?


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Old 01-25-10, 07:38 PM
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Question Create joints on existing jointless concrete driveway?

I have a concrete driveway in Texas measuring about 100 x 20 ft on a slope built in 2007. I don't know what the foundation looks like or the thickness, but have a call in to the builder to find out. It doesn't have a single joint, so of course now it has 4 cracks that each span with width of the drive.

I want to seal these cracks to a smooth finish and create proper clean straight control joints and would welcome and ideas or experience from readers. I have no experience with this.

One idea was to clean out the cracks fill with cement and then about 6 feet away create a straight control joint using a rotary cutter (not sure what the proper name is for this tool and whether or not it's something you can rent). Would that work? Is it possible to repair cracks to a smooth finish if you now have proper control joints? Is it possible to cut control joints? Can that tool cut deep enough (if the concrete is say, 6 to 8 inches thick?).

Another idea which sounds more expensive was to cut out a 1 to 2 foot wide strip out of the concrete to include the crack (using the rotary cutting tool and back hoe) and then re-pour using one of those edges as the new joint). Is this a better idea?

Any suggestions appreciated. Thanks in advance,

Jim

PS. When do you use a contraction joint versus an expansion joint?
 
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Old 01-26-10, 05:16 AM
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It's too late for joints now. They need to be placed when the concrete is poured, or the concrete will create its own joints by cracking. Simply filling the existing cracks in will not fix them. In fact, there's no way I know of to actually "fix" a crack in concrete. Temperature fluctuations will cause the concrete to expand and contract a bit, which will open and close the cracks as they move.
The only way the new joints would do anything at all is if they are cut entirely through the slab. (Joints that are cut or tooled at the time of the pour are only 1/4 of the way through the slab, not all the way through.)
By the way, all cut or tooled joints in a slab are contraction joints, not expansion joints. They are also called crack control joints, because they create a weak place in the slab to make it crack there instead of randomly when the concrete shrinks as it cures.
Expansion joints on the other hand, are those which go all the way through the slab and are filled with a compressible material like the black fiber strips, closed cell foam, rubber, or wood. They are usually used where the new slab butts up against an existing rigid structure like a brick facade, garage slab, or concrete curb and gutter. An expansion joint acts as a shock absorber because the compressible material takes the force of any movement in the new concrete instead of the slab taking it and cracking.
A typical driveway is 4 inches thick. You can cut all the way through it if you rent a concrete saw with a DIAMOND BLADE, not a fiber blade. It would take forever with a fiber blade and you would go through several of them before the jobs was done because they keep wearing down. The blade must be a 14 inch blade, because a 12 inch blade will not cut all the way through a 4 inch thick slab. If your plan has even a chance of working, you need to cut entirely through the slab and fill the resulting gaps/joints with backer rod and caulk. That way, your existing crack patches may possibly hold up. This is because there will be a 1/4 to 3/8 inch gap (width of the saw cut) between each sawed section. When the concrete expands and contracts with temperature fluctuations, the backer rod and caulk will take the pressure instead of the existing cracks. If your concrete is actually thicker than 4 inches, you'll need to hire a concrete cutting company to come out and saw it with one of the larger walk-behind saws.
In reality, a 20 foot wide drive should also have a joint running lengthways up the center in addition to those running across its width every 10 feet. On your driveway, the sections should all measure 10ft x 10 ft. Sections larger than that are too big.
Good luck.
 

Last edited by Pecos; 01-26-10 at 05:25 AM. Reason: more info
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Old 01-26-10, 11:28 AM
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Thanks

Thank you Pecos.

So contraction joints that extend only a quarter of the way through the concrete only control cracking during curing, not cracking from expansion/contraction from temperature/weather changes over time, correct?

If I cut expansion joints all the way though to create sections, then

1. Do you think I could repair and finish the cracks to a clean finish so that it doesn't look like a patch up job? (right now the color of the drive is a bright yellowish white color)

2. If yes to 1, will the cracks repair continuously break down needing repair over and over? Would this justify considering removing a strip of driveway around the crack and repouring and having one edge of the strip be a control joint? Is that an expensive job to hire a contractor to do?

3. There's a about 35 feet between the cracks. Could I get away with larger sections than 10 x 10?

Thanks - Jim
 
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Old 01-26-10, 01:23 PM
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Control joints are primarily to control shrinkage cracks during curing, which is why they are meant to be placed as soon as possible. Shrinkage cracking usually occurs within the first few days after the pour. But they also create weak places for the slab to crack during other movement as well. These other movements could be from freeze/thaw cycles, concrete expanding and contracting from extreme heat-ups and cool downs, extremely heavy loads placed on the concrete, or other types of ground movement.
It's doubtful that you could patch the cracks so they don't look patched. Not even professionals can do so. This is because patch materials are typically different colors than the existing concrete. Even if you got it to match initially, as the concrete ages and turns more of a tan color, the patches would likely show up again. And yes, the patch material would most likely have to be replaced/repaired on an ongoing basis.
Cutting out the cracks is certainly an option, but the new concrete probably wouldn't match the old colorwise either. You may consider using stamped or stained concrete instead, to give it a more decorative look. You'd be creating bands of color and texture between the existing plain concrete sections. It would look like it was supposed to be that way instead of a patch job. Pricing is completely dependant upon the individual contractor and the finish chosen.
Based on the size of your driveway, it's likely to crack in some more places over time. The joint spacing I described would be best to control future cracking, especially the one up the center of the drive. Depending on where the cracks are located though, the 10 foot sections up the drive may or may not fit in with the cut- out places and joints being consistently spaced.
 
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Old 01-29-10, 06:57 PM
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Create joints on existing jointless concrete driveway?

That was a good & accurate description offered by Pecos.

However, my factory training in decorative concrete suggest correcting the control joints, to help control where future cracks may occur. Recommended at least every 15' and cut 1/3 of the depth of the concrete.

A concrete crack repair system will need an overlay of some type as they will show as a repair. No way to blend with existing concrete.

Pecos suggestion using decorative bands would be the most economical solution.

Instead of replacing 1ft' to 2' of concrete, I would suggest applying a concrete crack repair system and an overlay, a decorative band across the driveway.

The challenge would be a uniform placement of the bands.
U are not limited to 1' or 2' bands, U could use 6' or 12, or any size to work out the uniformity of the placement of the bands.

You could use an overlay with stencil's to create the look of bricks, cobblestone, random stone, etc.

You could us a simple concrete dressing with concrete Grey for a blended and less decorative look.

or apply a concrete dressing over the whole driveway.

Visit the link below for concrete dressing information and other concrete driveway resurfacing information

Resurfacer

Ardex Technolocial Pioneering Self Leveling Self Dryng Cements
 
 

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