Does cement (Quickcrete, specifically) expand when it cures?

[MichaelD]

I don't know. Ergo this post.

Thinking of filling some PVC pipes (3" diameter, 24" long) with cement. I plan on assaulting my next door neighbor...er, filling some speaker stands I'm building.

If the cement is going to expand, I'll need to leave some "room" at the top and not fill the pipes completely.

Get busy and answer me. Please. :beer:

 

[Jmmsbnd007]

Yes. No. I don't know. I'm tired

 

[KK]

whats it say on the bag?

KK

PS. I dont think it expands or you'd have some funky sidewalks.

 

[HappyPuppy]

Dude, cement is not like water. It does not freeze and expand, it cures chemically. You would have no problem putting it in your PVC.

I still think you should consider the insulating foam, though.

 

[vi edit]

If anything, it shrinks a bit. I've help my Dad pour countless foundations and footings and I've never seen concrete expand. The only time it would expand is if it got water seeped into it and it got cold enough to freeze the water. That can make it expand.

 

[Amorphus]

wait, you're filling the PVC tubing? that just brings the center of gravity up. make a hollow base and fill that.

 

[MichaelD]

Originally posted by: Amorphus
wait, you're filling the PVC tubing? that just brings the center of gravity up. make a hollow base and fill that.

That's exactly what I thought when I first started researching building my own stands.

But many folks have explained that since the weight is concentrated straight up and down, and "focused" on one small point (i.e. the end of the PVC) that it makes it more stable.

 

[RagingBITCH]

Are the pipes going to be in direct sunlight by chance? Concrete does expand and contract, just minimally though.

 

[MichaelD]

Originally posted by: RagingBITCH
Are the pipes going to be in direct sunlight by chance? Concrete does expand and contract, just minimally though.

Hmm...nah, not really. I'm assuming the room will have windows, but it will be climate-controlled. Shouldn't be a problem.

Quickcrete is sounding better and better. :beer: That's the stuff you just mix with water and be done with it, right? I'll buy one of those disposable "Homer buckets" from HD and a trowel. Done.

 

[huesmann]

The weight being concentrated doesn't make it stable at all. In fact, if the things tip over, they're more likely to go down than if you didn't fill 'em with concrete simply due to the bending moment of the additional weight.

 

[MichaelD]

Originally posted by: huesmann
The weight being concentrated doesn't make it stable at all. In fact, if the things tip over, they're more likely to go down than if you didn't fill 'em with concrete simply due to the bending moment of the additional weight.

That DOES make sense. But then how come every stand you can buy, including the VERY expensive "pro" ones are fillable?

 

[Shockwave]

Dont fully fill it, fill like the bottom 1/3.

 

[NutBucket]

Originally posted by: Shockwave
Dont fully fill it, fill like the bottom 1/3.

Agreed. Make a fillable base instead

 

[NokiaDude]

You know why they have spaces in-between each slab of concrete on sidewalks? IT'S BECASUE IT EXPANDS WHEN WARM!!!

 

[Sukhoi]

Originally posted by: MichaelD

Originally posted by: huesmann
The weight being concentrated doesn't make it stable at all. In fact, if the things tip over, they're more likely to go down than if you didn't fill 'em with concrete simply due to the bending moment of the additional weight.

That DOES make sense. But then how come every stand you can buy, including the VERY expensive "pro" ones are fillable?

They probably get filled with stuff to dampen vibrations.

 

[RagingBITCH]

Originally posted by: NokiaDude
You know why they have spaces in-between each slab of concrete on sidewalks? IT'S BECASUE IT EXPANDS WHEN WARM!!!

Very minimally though. That's under 12 hours of direct sunlight. You do see huge cracks in the street sometimes but rarely the driveway. I did mention it above and direct sunglight/heat will not be a problem for Michael. Just chill out.

 

[silverpig]

Concrete doesn't expand as it hardens. The spaces in the sidewalk are to account for expansion/contraction that it undergoes with the temperature swings of 2 am in January with 1 pm in July.

 

[WinkOsmosis]

Originally posted by: RagingBITCH

Originally posted by: NokiaDude
You know why they have spaces in-between each slab of concrete on sidewalks? IT'S BECASUE IT EXPANDS WHEN WARM!!!

Very minimally though. That's under 12 hours of direct sunlight. You do see huge cracks in the street sometimes but rarely the driveway. I did mention it above and direct sunglight/heat will not be a problem for Michael. Just chill out.

Those cracks are from the soil moving and clay expanding and contracting.

 

[KenGr]

No, the expansion joints are for the concrete expanding and contracting, not the soil. But it's not a problem on small sections. That's why driveways and streets only have joints every 20 feet or more. Curing doesn't cause a noticeable dimensional change but it does cause a change. When you pour columns and slabs while building a building, the slabs (floors) are supported by shoring (bracing). As the concrete columns harden, some load is taken off the shoring because the columns expand very slightly.

None of thes has any bearing on speaker stands at all. Just keep the concrete only in the lower part of the stand. AND... DON'T CALL IT CEMENT!!!!

 

[MichaelD]

What happens if I call it cement? Does it crack?

Thanks much guys. It has been said that the entire cummulative knowledge of mankind can be found on ATOT. Today has proven this adage correct. :wine:

 

[Chaotic42]

Yeah, I agree with everyone, put the weight at the bottom. It would be best to have a round base filled with concrete (or sand) and then have the pipe with the speaker on it.

I'd fill the pipe, because the speaker will vibrate the pipe (especially if the pipe is fastened at the bottom) and it won't sound good.

 

[CFster]

Don't believe regular concrete expands...

But they have this stuff called "hydraulic cement" that expands to fill cracks on purpose I heard.

 

[Squisher]

The reason you want to fill it entirely is to dampen vibrations.

The only cement that expands when cured is hydraulic cement.

 

[tooltime]

i've used it a few times and don't remember that happening

 

[Jmmsbnd007]

Originally posted by: Chaotic42
Yeah, I agree with everyone, put the weight at the bottom. It would be best to have a round base filled with concrete (or sand) and then have the pipe with the speaker on it.

I'd fill the pipe, because the speaker will vibrate the pipe (especially if the pipe is fastened at the bottom) and it won't sound good.

Hollow base filled with Quickcrete and have the pipe filled with some kind of vibe-absorber.