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What is your base for concrete and your reasons?

11 replies [Last post]
Mverick
User offline. Last seen 3 years 3 weeks ago.

Figured I had some questions to ask and see what others had thought about them.

I'm in St. Louis area. So, lots of freeze thaw cycles.

Dig in 6in usually, depending on sight and put in 4in of 3/4 clean gravel.

Depending on location, will also put a pipe in the low area of the gravel, so any water under pad comes out of pad and doesn't build there.

Never use sand, it hold water.

We have a lot of clay and it will heave.

Never pour on dirt.

Our pads are basically floating pads. Floating on the gravel. Walkways the same.

MC
User offline. Last seen 3 years 5 days ago.
here we use 4" compacted abc

here we use 4" compacted abc (aggregate base course) which is sand and either gravel or recycled concrete. Concrete placed at 4" thick for mostly everything except for when heavier loads will be placed or driven on.

ronin1975
User offline. Last seen 1 year 28 weeks ago.
I have never, ever, EVER

I have never, ever, EVER poured anything on gravel.
Gravel has clay in it, clay heaves and holds water.
Sand does not hold water. I'm really not sure how you think it does. Have you ever seen anyone pour a freeway on gravel?
I'm pretty certain ACI specifies sand for a substrate.
But hey I don't know everything. There's my dissenting opinion for what its worth.

I have read two of your posts now and while I disagree with some of your methods I won't judge you.
You will NOT be allowed to date my sister though.

ronin1975
User offline. Last seen 1 year 28 weeks ago.
On another note they are

On another note they are doing some amazing things with geo membranes now adays. In situations that warrant the cost they are amazing.

MC
User offline. Last seen 3 years 5 days ago.
Highways arent poured on a

Highways arent poured on a bed of sand ..thats funny. They use the same thing we use here. ABC..aggregate base course which is a mixture of sand and rock or either sand and recycled concrete. You need to have a high level of compaction and sand alone does not compact at all. Sand/gravel mix compacts very well and is what is used under all paving. Im from the West Coast though so I dont know what goes on back East

Mverick
User offline. Last seen 3 years 3 weeks ago.
3/4 clean has no clay in it.

3/4 clean has no clay in it. It's washed gravel. Limestone that is blasted out of a quarry and sized.

It packs well. But it isn't a wall base material.

Take a 5 gallon bucket with holes in the bottom of 3/4 clean gravel and a 5 gallon bucket with holes in the bottom of sand and pour water in them. Let them drain and put in the deep freeze and see what happens.

Sand holds water. It's a good filter. But it holds water.

suntacsys
User offline. Last seen 3 years 3 weeks ago.
nysdot places conc on ' item

nysdot places conc on ' item # 4 ', manufactured gravel; ga specs ' gabc ', also manufactured,,, h/o's & diy-er's use sand,,, never saw a spec that call'd for sand - county, state, fed, private arch/eng, OR municipal.

best [the original] saw-your-sister's-pic-i'm-busy-that-nite yic-yac

EDIT NUMERO UNO - forgot to mention neither of the abovereferenced mtls include ANY clay,,, neither does pa, ct, nj, or md dot's,,, sc does use sand-clay mtl for asphalt roads but not for conc.
expect that sand/clay MAY contribute to random conc cracking but, if i had to bet, would pick incorrect jnt pattern or wrong timing to install same over base mtls & give points :-)

Mverick
User offline. Last seen 3 years 3 weeks ago.
In our area which have heavy

In our area which have heavy freeze thaw cycles.

I can show you a whole bunch of concrete pads that are broken because of using the Sand for a base.

One in front of my house is a prime example. It don't pack so large trucks turning around on it is bad. And during winter if water get's under it will freeze and heave.

We have a lot of clay soil in our area. So, we get a lot of heaving anyway. The 3/4 clean gravel, for us, allows a little shift room if it pushes hard. If I did a compacted solid base. I'd get it heaving. Unless I did it under the 42in freeze depth. And, that's a lot of concrete for a driveway. LOL...

My uncles all poured concrete on sand in the old day's too. But, I can show almost every one of theres that's heaved and cracked. They still believe in that method. Even after I bring up the Freeze thing.

ronin1975
User offline. Last seen 1 year 28 weeks ago.
I must be living in a bubble

I must be living in a bubble here in Michigan. lol My entire career, I have never seen one print that specs anything but sand. Even the few commercial jobs I've been on. Alot of the old school guys I've talked to over the years swear by it.
Show me ten cracked slabs that you attribute to using sand and I'll show you another ten that aren't cracked.
Sand is a good base for allowing water to go deeper or flow away from the slab. I've torn out alot of slabs poured on gravel because of the clay content in it heaving and holding water. As far as using rock for a base, unless it's with a sand mix how do you get good compaction? As far as Michigan DOT? When I'm sitting in a traffic jam next to a paver it sure looks like sand to me. I'm actually quite stunned, I thought everyone used sand.
Hey though, I certainly don't claim that my way is the only right way. This is just what I have experienced and been taught by grouchy old alcoholics who had way more time in then me.

ronin1975
User offline. Last seen 1 year 28 weeks ago.
When you guys say 3/4 gravel

When you guys say 3/4 gravel I'm assuming what you really mean is 3/4 crushed stone. Something like a 6a? I understand where you are coming from now. Whenever I hear gravel I think or road gravel, not crushed limestone. Pitfall of growing up on a bulldozer. My apologies for not paying attention before.
Just curious... anyone still have their aci book and care to tell us what it says for resi and com?

MC
User offline. Last seen 3 years 5 days ago.
it must be a location thing

it must be a location thing because here on the west coast I have never seen any concrete slab spec'd with a sand base. Everything is spec'd for abc (sand and rock) compacted to at least 90%.
I cant see how placing on sand would be good no matter where you are though because of it not being able to compact. Placing concrete on a fluffy subgrade can never be good .

Mverick
User offline. Last seen 3 years 3 weeks ago.
LOL, What I really mean is

LOL,

What I really mean is Gravel. I said 3/4 clean. LOL

I didn't say, grade 8. That has lots of fines. What most driveway's have when they don't want to pay money to do asphalt or Concrete. And then a cheap asphalt or Concrete guy comes in and say's I can pour for $4 a sq/ft and you have a good rock base. Which they don't. Set forms, Pour, Finish and take the money. Or, throw down sand over the gravel and then when someone drives over the corner it cracks.

We, don't pour on that. We charge the money to pour on 3/4 clean gravel. It gets great drainage. It has a solid compaction.

The Clean part means it doesn't have all the fines.

But, Gravel, is really crushed rock too. They all get run through a crusher.

A different material is SLAG. We have lots of that here too. Steel Mill in the Area.

If you also look at the commercial specs for road base, they go pretty deep. It's not a 4in base. They also have a lot more going on under those pads. They don't just throw sand/gravel/nothing down and pour over it. Highways are a prime example aren't they. Deep sub base.

If you pack on 4in of sand. How are you getting a solid base? Sand doesn't compact? Guarantee 3/4 clean gravel will shift less then sand.

If you go to the beach and pick up sand. Let water drain out of your hand and freeze the sand. It still holds enough water to expand during freezing.

Your right. A lot of the drinkin buddies and my family still believe in the sand method. Also, pouring over a old gravel driveway. It's how they learned to do it. They also have no idea of polymerized concrete's. Or Low slump with plasticizers for added strength. So, you can pour a 2in slump that finishes like a 5in slump. They also still will put water on a slab to pretty up the finish. And also seal the surface.

Just like guy's using Hardener colors in freeze zones. Simple understanding of what it does should tell you not to use it... Can you get lucky? Yes. But, how it's designed means it's a bad idea.

I'm not pouring for $4 a sq/ft. I don't pour standard concrete because guy's are way to cheap to do a proper job. I'm getting $18 a sq/ft. People want cheap. Don't call me. I tell people they can get it cheaper from others. I don't pour cheap.

If it's working for you great.