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concrete question

Started by Dan_Shade, October 24, 2014, 07:32:02 PM

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Dan_Shade

Anybody know the advantages/disadvantages of using 2000 psi or 3000 psi in a footer?
Woodmizer LT40HDG25 / Stihl 066 alaskan
lots of dull bands and chains

There's a fine line between turning firewood into beautiful things and beautiful things into firewood.

pigman

The advantage of 2000 psi concrete is that it is usually cheaper than higher psi concrete. The disadvantage is that if there is a concentrated compression load higher than 2000 psi, then the concrete could crush.
Things turn out best for people who make the best of how things turn out.

Banjo picker

I was a concrete contractor for over 20 years get the 3000 psi for the footing.... if you don't want to up it to 4000... the price per yard difference is not that much,  probably not much more than $10 more.  I will ask what is the footer for ?  Banjo
Never explain, your friends don't need it, and your enemies won't believe you any way.

POSTON WIDEHEAD

Dan, when I poured my drive way and parking area, I went ahead at poured 4000 psi. I knew I would be driving tractor and backhoes and heavy trailers across it.
When I poured my house footing, I used 3500 psi. Personally I would not go below 3000 psi. But thats just me.
The older I get I wish my body could Re-Gen.

sandhills

Ok, I've helped on many pours for friends and neighbors, I know what the fiber mesh stuff is and how to re bar the regular but never heard of concrete rated in psi.  Would someone mind enlightening my tiny little mind on this, I really hope to be pouring footings and a basement this spring, bank and God willing of course.

Ljohnsaw

And... How does that relate to "sack" mix?

Out here, they refer to the mix as to how may sacks of Portland go in a 1 yard mix.  It's been quite awhile (when concrete cost $54/yd :D) but I *think* the standard is 4 sack but I would always buy 5 sack as it was only $10 or 12 more - well worth it for the extra strength.  Never had issues with cracking.
John Sawicky

Just North-East of Sacramento...

SkyTrak 9038, Ford 545D FEL, Davis Little Monster backhoe, Case 16+4 Trencher, Home Built 42" capacity/36" cut Bandmill up to 54' long - using it all to build a timber frame cabin.

WmFritz

It's common to use 2000 psi concrete for lightweight applications, usually adding air and/or some kind of lightweight aggregate. 3000- 4000 psi should be used for footings with rebar.

Sandhills, the more Portland cement and less sand used in the mix, the higher the psi. Also, the more Portland cement in the mix, the easier it is to get a nice finish. More cement around the aggregate.
~Bill

2012 Homebuilt Bandmill
1959 Detroit built Ferguson TO35

WmFritz

Quote from: ljohnsaw on October 25, 2014, 12:27:40 AM
And... How does that relate to "sack" mix?

This is kinda rule of thumb... variables apply like aggregate size, amount of water added, etc.


Bag Mix/psi Chart

4 Bag 1500 psi

4.5 Bag 2000 psi

5 Bag 2500 psi

5.5 Bag 3000 psi

6 Bag 3500 psi

6.5 Bag 4000 psi
~Bill

2012 Homebuilt Bandmill
1959 Detroit built Ferguson TO35

Ljohnsaw

Bill,
Thanks for the list.  I'll keep that for when I pour my footing, possibly this year if the drought holds ::)
John Sawicky

Just North-East of Sacramento...

SkyTrak 9038, Ford 545D FEL, Davis Little Monster backhoe, Case 16+4 Trencher, Home Built 42" capacity/36" cut Bandmill up to 54' long - using it all to build a timber frame cabin.

red oaks lumber

i always get the 4000 psi mix, concrete is one area i won't cut corners :) the few dollars i might save won't seem like much savings if the concrete fails and i have to redo it.
the experts think i do things wrong
over 18 million b.f. processed and 7341 happy customers i disagree

ely

They had a 7 sack mix when I did my house slab and footing I went with that. 3500 is the minimum I will order.

sandhills

Thanks Bill, I've never heard of it put in psi terms before, and red oaks I can't agree more, nothing worse than a bad pour.  It's hard/expensive enough to do it the first time around.

Dan_Shade

thanks guys.  I'm putting up a garage.

How many yards are in a mix?
Woodmizer LT40HDG25 / Stihl 066 alaskan
lots of dull bands and chains

There's a fine line between turning firewood into beautiful things and beautiful things into firewood.

Banjo picker

psi = pounds per square inch....so how they test it is make a cylinder ... they are round and about 6 inches across and a foot tall....they have to be made the correct way for the test to work...(I was a certified concrete tech. for a good while)If anybody is interested I will explain further.... anyway after the cylinder has been cured preferably in a vat of water for 21 days they take it out and put it in a machine and squeeze it for both the 6" round ends...you do the math (pi r sq) to get the surface area .. A cylinder as I just described that was made out of 5000 psi concrete would have to take more than 47100 pounds of pressure before the cylinder explodes....If I did the math right.. Banjo
Never explain, your friends don't need it, and your enemies won't believe you any way.

sandhills

Banjo, the wealth of knowledge around here never ceases to amaze me, I had no clue they pressure check concrete, heck I'm just happy if I get it smooth, flat, and it cures without cracking all to heck  :D.
Dan, I'm not sure I'm answering your question right but the trucks around here haul 10 yards (legally) but you can order the amount desired per load.  The last pour I helped on wires got crossed and an extra 10 yards showed up while we were unloading what we thought was our last truck, oops  ::).

Ljohnsaw

Quote from: sandhills on October 25, 2014, 12:14:40 PM
<<snip>>
The last pour I helped on wires got crossed and an extra 10 yards showed up while we were unloading what we thought was our last truck, oops  ::).
Always have additional areas to pour the extra.  A little walkway, pad, etc.  A truck usually has 1/2 to 3/4 yard more just to be sure and is typically free (unless it's a mix-on-site truck).  If you did your math a little wrong, it might cover it or you might end up with more than a yard extra.  But having an "extra" 10 yards, YIKES! :o
John Sawicky

Just North-East of Sacramento...

SkyTrak 9038, Ford 545D FEL, Davis Little Monster backhoe, Case 16+4 Trencher, Home Built 42" capacity/36" cut Bandmill up to 54' long - using it all to build a timber frame cabin.

sandhills

ya we always have a spot to go with a "little" extra  :D  Think farm and feedlot, its easy to use up some, but a whole load is a little more time consuming when you don't have the dirt work or forms ready  :D.  We got it done though.  I hate pouring cement!  I'm sure those that do it a lot, or for a living don't think twice about it but that is hard work, I don't care who you are.

cowtipper

Quote from: Banjo picker on October 25, 2014, 09:43:53 AM
psi = pounds per square inch....so how they test it is make a cylinder ... they are round and about 6 inches across and a foot tall....they have to be made the correct way for the test to work...(I was a certified concrete tech. for a good while)If anybody is interested I will explain further.... anyway after the cylinder has been cured preferably in a vat of water for 21 days they take it out and put it in a machine and squeeze it for both the 6" round ends...you do the math (pi r sq) to get the surface area .. A cylinder as I just described that was made out of 5000 psi concrete would have to take more than 47100 pounds of pressure before the cylinder explodes....If I did the math right.. Banjo

Something like this?  https://www.youtube.com/watch?v=eAUfJ90QtDY

Banjo picker

Funny you should pick that video... I have poured a lot of concrete for Vulcan Materials... Did a complete plant for them in Cherokee Alabama and another near Searcy Arkansas...and many small additions over the southeast.  Banjo
Never explain, your friends don't need it, and your enemies won't believe you any way.

Magicman

Most times when a large pour is made such as a highway or a building, you will see those test cylinders filled and set aside for testing.  This verifies that the correct strength mix was used as specified.
Knothole Sawmill, LLC     '98 Wood-Mizer LT40SuperHydraulic   WM Million BF Club Member   WM Pro Sawyer Network

It's Weird being the Same Age as Old People

Never allow your "need" to make money to exceed your "desire" to provide quality service.....The Magicman

woodmills1

the amount of water is so very related to strength

majic man that is called the slump test  :D
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Banjo picker

If it fails the slump test...no cylinder is made.  The whole load goes back.  Banjo
Never explain, your friends don't need it, and your enemies won't believe you any way.

scsmith42

We used to require that our test cylinders be cured on site - in the exact same conditions as the pour.  That way the test results were more accurate. This is especially important when pours are made in extremely hot weather, or extremely cold weather.  Sometimes we even required that extra cylinders be poured, signed, dated and then buried next to the slab.  That way, long term if there was a problem we would have more cylinders available to check - and if necessary to use as evidence in having the quality problems corrected.

Usually if the crew handling the concrete is complaining, you have the right mix!  The more water, the higher the slump, and the more likelihood that your concrete will crack.  Personally I prefer my mix to be in the 3-1/2" - 4-1/2" slump range.  Basically, the drier the mix, the stronger it will be.

Age is another factor to consider, as concrete starts to set up once it is mixed, and if too much time passes between initial mixing and pouring it will have problems.  Most commercial sites will not allow concrete to be poured once it is 1-1/2 hours old (ie if the batch was mixed at the plant at 2 pm, you better have it all poured and placed by 3:30. 

A couple of other things to keep in mind - don't let a fresh concrete pour freeze within 3 days of when it was poured.  If so, it may lose a lot of strength. Additionally, the ideal cure temperature for concrete is around 55 degrees F, and the longer that the slab cures at a cool temperature the stronger it will usually be (and more crack free).  For this reason, I prefer large slab pours (for personal use) to take place in either fall or spring (but preferably the fall).

Grade preparation goes a long way to preventing future problems.  Get rid of all of the topsoil and make sure that the subgrade is extremely well compacted.

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and a mix of log handling heavy equipment.

Banjo picker

I had one job that required temp of the concrete to be and stay below 90 deg.  It was a summer time job.  We had ice boxes set up on the batch site and exchanged water for bags of ice.  Also had ice boxes on the job site if additional water was needed.  Trucks would show up looking like an ice cream freezer all frosted up... We never lost any concrete.  I have made bridge deck pours in winter...cover the slab with insulated blankets and cover the side with plastic and keep salamanders running for several days... inspectors use a  high-low thermometer ... registers the highest temp and the lowest temp... You are right about the slump...4 inch will give you a good product.  Banjo
Never explain, your friends don't need it, and your enemies won't believe you any way.

Magicman

Knothole Sawmill, LLC     '98 Wood-Mizer LT40SuperHydraulic   WM Million BF Club Member   WM Pro Sawyer Network

It's Weird being the Same Age as Old People

Never allow your "need" to make money to exceed your "desire" to provide quality service.....The Magicman

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