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Old 07-18-2012, 01:54 PM   #1
MichaelD
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Default Why do they cut lines in concrete?

The sidewalk outside my building was recently redone by the city. They poured like a 50-foot long slab and then they cut "lines" in it to make it look like individual 5-foot sections. The lines don't go all the way through; they are only about 1/4" deep.

Why do they do that? Just for aesthetic reasons? Sounds like a waste of manpower to me. What's wrong with a 50-foot slab of concrete that looks like a 50-foot slab of concrete? Confusing concrete construction is confusing.
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Old 07-18-2012, 01:54 PM   #2
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So that when it cracks, the cracks follow the geometric lines rather than make ugly jagged lines.
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Old 07-18-2012, 01:55 PM   #3
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Localizes cracking and allow for expansion.

Last edited by rcpratt; 07-18-2012 at 01:58 PM.
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Old 07-18-2012, 01:56 PM   #4
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Are you guys on crack?
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Old 07-18-2012, 01:57 PM   #5
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But...how do they know that the cracks will follow the line they cut? I've seen concrete cracked in the corner. :???:
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Old 07-18-2012, 01:58 PM   #6
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Quote:
Originally Posted by oldsmoboat View Post
Are you guys on crack?
Ah, here it comes.

"This thread is now about crack."

Two days later:

"Did you hear MichaelD was banned? Yeah, he started a thread about CRACK that got outta control!!! Dumb bastard!"
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Old 07-18-2012, 01:58 PM   #7
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it's more likely to crack where the concrete is thin - where they cut
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Old 07-18-2012, 01:59 PM   #8
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Quote:
Originally Posted by MichaelD View Post
But...how do they know that the cracks will follow the line they cut? I've seen concrete cracked in the corner. :???:
Expansion and contraction will /tend/ to follow the path of least resistance. It isn't guaranteed cracks will follow the joint, but they will enough times to make the small amount of work worthwhile.
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Old 07-18-2012, 02:01 PM   #9
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Expansion and contraction will /tend/ to follow the path of least resistance. It isn't guaranteed cracks will follow the joint, but they will enough times to make the small amount of work worthwhile.
That does make sense. Thanks. Now, maybe I should come back at night with my cordless rotary tool and carve out all kinds of squiggly lines and see what kind of awesome cracks happen this winter!
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Old 07-18-2012, 02:03 PM   #10
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Quote:
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But...how do they know the crack line they cut? I've seen crack in the corner. :???:
wait...wut? you get crack off the corner and cut it? do you use a razor and a mirror like they do on TV?
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Old 07-18-2012, 02:04 PM   #11
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maybe helps with drainage also?
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Old 07-18-2012, 02:04 PM   #12
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I've thought about why they did it. I wasn't really sure. But, localizing cracks makes a lot more sense than them just trying to fuck with OCD people.
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Old 07-18-2012, 02:06 PM   #13
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Is this thread about crack?
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Old 07-18-2012, 02:06 PM   #14
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I thought it was so when the concrete settles the cracks would happen in the lines?
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Old 07-18-2012, 02:06 PM   #15
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So you have something to blame when your mother breaks her back.
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Old 07-18-2012, 02:07 PM   #16
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Quote:
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I've thought about why they did it. I wasn't really sure. But, localizing cracks makes a lot more sense than them just trying to fuck with OCD people.
It does..Unless you are Gary Busey.
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Old 07-18-2012, 02:09 PM   #17
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This thread cracks me up!
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Old 07-18-2012, 02:10 PM   #18
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Quote:
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But, localizing cracks makes a lot more sense than them just trying to fuck with OCD people.
Hahahahahahaha!!
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Old 07-18-2012, 02:19 PM   #19
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My guess is they act as expansion/cracking points as well as drainage to some degree. Instead of water sitting on the surface it is more likely to fill the crack, when it freezes it is more likely to crack in that one spot instead of randomly. If the ground is not well prepped it's still possible for cracks to appear elsewhere, but these lines limit it.

They also provide kids with something to do by trying not to walk on them.
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Old 07-18-2012, 02:22 PM   #20
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Quote:
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But...how do they know that the cracks will follow the line they cut? I've seen concrete cracked in the corner. :???:
the same way scoring glass works. cracks will follow wherever is weakest, even if it's only 5% weaker than the surrounding area.
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Old 07-18-2012, 02:23 PM   #21
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Quote:
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That does make sense. Thanks. Now, maybe I should come back at night with my cordless rotary tool and carve out all kinds of squiggly lines and see what kind of awesome cracks happen this winter!
sure, and when you get arrested for vandalism of city property, be sure and tell them that you did it for the future!
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Old 07-18-2012, 02:26 PM   #22
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Quote:
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But...how do they know that the cracks will follow the line they cut? I've seen concrete cracked in the corner. :???:
Concrete slabs will move in respect to each other based on weather conditions, soils, moisture, traffic, loads, etc.

Because of all of these factors, there will be stress concentrations in the pavement. By cutting the pavement, you try to limit the area and extent of cracking. If the pavement wasn't cut, the pavement would likely crack in random areas.

Also, it is quicker and cheaper to pour a 100' section of concrete, then make nine relief cuts than to put together 10 slabs compared to forming and pouring 10 individual panels.

Corner cracks are usually and indication that there are poor soils under the pavement, the road gets more traffic than designed, or poor load transfer. As the panels move in respect to each other, they tend to concentrate the loads at the corners. That's where the slabs will break.
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Old 07-18-2012, 02:30 PM   #23
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Quote:
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wait...wut? you get crack off the corner and cut it? do you use a razor and a mirror like they do on TV?
i believe crack is for smoking. coke is for snorting off a mirror. i could be wrong.
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Old 07-18-2012, 02:33 PM   #24
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<--is definitely a bit OCD. I guess it shows?
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Old 07-18-2012, 02:34 PM   #25
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Originally Posted by Red Squirrel View Post
My guess is they act as expansion/cracking points as well as drainage to some degree. Instead of water sitting on the surface it is more likely to fill the crack, when it freezes it is more likely to crack in that one spot instead of randomly. If the ground is not well prepped it's still possible for cracks to appear elsewhere, but these lines limit it.

They also provide kids with something to do by trying not to walk on them.
Some pavements are tined allong the travel direction to improve the friction of the road, but not for drainage, per se.

Highway departments try to seal the joints between slabs. The water carries sand and other materials that limit how well the slabs move against each other. If too much sand gets stuck in the joint, the slab can lock up, which leads to faulting and other bad things.
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