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Concrete slump question.

Started by Dave Shepard, October 22, 2008, 10:20:04 PM

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Dave Shepard

Anyone know if there is a standard amount of slump allowed for concrete? I'm sure there must be. We did a small knee wall today, and the concrete was so wet, it lifted the top row of ICFs off. >:( There is a step in the top of the form, which we made by making a blockout from blue board insulation. The 'crete was so wet, that when it flowed under the block out, it lifted right off. I don't think it would have happened if it was stiffer. This is our first experience with the ICF's. The driver had an extra two yards on, and when he dumped it in the yard, it made a pile about 12' across, and maybe a foot and a half deep.


Dave
Wood-Mizer LT40HDD51-WR Wireless, Kubota L48, Honda Rincon 650, TJ208 G-S, and a 60"LogRite!

Mooseherder

Wow, were you able to salvage the job?
That is a dirty curve ball.  Hope it worked out.

isawlogs

 I dont know much about ciment , but what I do know the driver would of stopped putting that soup mix in my forms ... theres flowing and then there is this ... ICF's are not suppose to start floating ................

Why did he have so much extra in the truck .. and why did he dump it where he did . ???
A man does not always grow wise as he grows old , but he always grows old as he grows wise .

   Marcel

Dave Shepard

As it turned out, the top of the second row was only about a 1/4" below our intended joist plate, so we leveled the form off there. We stuck some rebar into the back, and will have to form up the next step for the stud wall. Not a huge setback, but it would have been nice to get it in one pour.

The extra concrete was for another job that they were doing, but they didn't need what he had on the truck. We had him pile it so we could put a rat slab in the crawl space. We didn't have the poly sheeting, and had to do a little raking, but we got the slab in. That saved having to get a $400 short load. Unfortunately it was a bit of shoveling work, as the excavator couldn't dump the 'crete in the basement with the forms in the way, but the boss did most of the shoveling. ;D All in all we saved the job, but what a mess!


Dave
Wood-Mizer LT40HDD51-WR Wireless, Kubota L48, Honda Rincon 650, TJ208 G-S, and a 60"LogRite!

bck

25 years ago I helped pour some walls for underground tanks. I remember we had to measure slump and get it right before we started pouring walls, I dont remember how much it was though. Seems like we poured it in a sleeve and lifted sleeve off and it was only allowed to drop a certian amount.

scsmith42

Dave, there are definitely recommendations for minimum and maximum concrete slumps.

In general, slump is relatd to the amount of water in the mix.  The lower the slump, the higher the cured strength of the concrete and reduced shrinkage (due to lower water amount in the mix).  There is a huge difference in strength, too.  For instance, a mix with 8 gallons of water per sack of Portland type 1 cement will usually test out around 2,700 - 3,500 psi at 28 days.  Reducing the amount of water per sack of cement from 8 gallons to 4 gallons will over double the strength of the concrete - up to 6000 - 7,500 lbs compressive strength.

Here are some slump recommendations from one of my manuscripts:

Reinforced foundations walls and footings:  6" max, 3" minimum
Unreinforced footings, caissons, and sub-structured walls:  4" max, 1" min
Reinforced slabs, beams, and walls:  6" max, 3" min
Building Columns:  6" max, 4" min
Pavements:  3" max, 1" min
Heavy mass construction:  3" max, 1" min
Bridge Decks:  4" max, 3" min
Sidewalk, driveway, snad slabs on ground:  6" max, 3" min.

I usually specify a 4-1/2" slump for all of my mixes, and in some instances will request a lower slump with a plastisizer added once the truck arrives at the site.  For instance, a truck can leave the batch plant with a 3" slump, and by adding the plastisizer they can increase the slump on site to around 4-1/2" for 45 minutes or so, without negatively impacting strength.

It's usually up to the person who orders the concrete to specify the slump.  From what I've observed, many contractors specify way too high of a slump in order to reduce the efforts required to work the concrete. 

You don't want concrete that is aged more than 45 minutes once it arrives at your location, and you want to have it in place no more than 1.5 hours after it's batched - and less is better.  In hot weather, you need to reduce these times by at least 1/3.

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moonhill

I have heard the saying " you place concrete, you don't pour it" .  In the end the worker should be slumped. 

Tim
This is a test, please stand by...

Larry

Quote from: Dave Shepard on October 22, 2008, 10:43:18 PM
The extra concrete was for another job that they were doing, but they didn't need what he had on the truck.

They could have mixed it wet for that other job...to ease placing and or finishing.  Concrete companies don't much care what you get for residential.  They are much more attentive on commercial work where the contractor may send a truck back because of improper slump.

Scott gave a lot of good information...and I agree with all of it.

Larry, making useful and beautiful things out of the most environmental friendly material on the planet.

We need to insure our customers understand the importance of our craft.

ely

generally speaking we always used a or started with a four inch slump, this was in general construction jobs i was on. sometimes we adjusted in the field a little after the  engineer left.

Raider Bill

For my ICF pours I used 6" slump. I also glued all the courses.
The First 70 years of childhood is always the hardest.

Dave Shepard

Thanks for all the replies. Raider Bill, what did you use for glue? The problem with EPS is that the solvents in most adhesives will eat away the foam. We used some expanding foam to plug some holes in the formwork, and it didn't eat the foam. Gorilla glue is the same stuff, and I saw that it is 100% solvent free. I am going to try that and see how well it bonds.

Now that we have some slump numbers, how do we measure it? Thanks.


Dave
Wood-Mizer LT40HDD51-WR Wireless, Kubota L48, Honda Rincon 650, TJ208 G-S, and a 60"LogRite!

Gary_C

There is a standard cone made for slump tests. If I remember right, it is a cone that is 12 inches high and 8 inches in diameter at the bottom and 4 inches in diameter at the top. You also have foot holds to keep it on the ground and handles to lift it off.

The way you are supposed to do the test is to fill the cone one third full and using just a steel rod, you rod it 25 times, fill another one third full and rod it 25 more times, and then fill it full and rod another 25 times. Wait a few seconds and then lift the cone straight off and measure how far the cone of concrete slumps. Not how high it stands.

With some experience, you can usually judge the slump just as the mix comes down the chute. However for large jobs and state jobs they will run a test.
Never take life seriously. Nobody gets out alive anyway.

DouginUtah


The concrete spec'ed by the ICF manufacturers is not what is normally used for flatwork, etc. It is more of a grout consistency made with different materials. Depending on rebar placement and width of the form the slump should be at least 6 and 7 would be better, from a lack of voids perspective.

The lower the slump the greater the necessity of using a mechanical vibrator. If you do have a lower slump and don't vibrate you will have voids.
Dave may live in an area which doesn't require as much rebar as here in seismic zone D (?), but I have always found that the two horizontal pieces of rebar on the top course were enough to hold it in place. Wait! I just remembered. You must also use (24") plastic zip ties down to the course below.

I have always used foam, especially under the first course, and nylon tape (on corners).
-Doug
When you hang around with good people, good things happen. -Darrell Waltrip

There is no need to say 'unleaded regular gas'. It's all unleaded. Just say 'regular gas'. It's not the 70s anymore. (At least that's what my wife tells me.)

---

Dave Shepard

I think I need to get some training on this stuff, if we are going to do it again. I have found some info on Logix online, but not too much. I'm hoping the dealer will have better info. The advantage for us is that we are rehabbing old houses, and it's all funky custom formwork. Using ICF's, we don't have to buy real forms, and we can just chop it up to fit the circumstances. I think after I get a little training, they will be a great way to do the type of work we are doing.


Wood-Mizer LT40HDD51-WR Wireless, Kubota L48, Honda Rincon 650, TJ208 G-S, and a 60"LogRite!

Raider Bill

I just layed a line of foam down on top of the blocks then set the next course.
I used windlok low expansion foam in a adjustable gun.

The first lift I set the block then went back and foamed. this way was a pain in the butt and wasted a lot of foam so the second lift I foamed as I went which worked out great.

Just make sure the blocks are lined up as once the foam sets up they are not coming apart with out ruining them.

I didn't tape the corners or tie the top course.
The First 70 years of childhood is always the hardest.

Dave Shepard

The logix website has 15 movies regarding installation. Wish I had known about that before I used them. :-\ They offer a couple of joist systems that would have solved our problem, without the time consuming blockout disaster. They specify a 6" slump for their form systems. Thanks to DouginUtah for the tip about the videos. 8)
Wood-Mizer LT40HDD51-WR Wireless, Kubota L48, Honda Rincon 650, TJ208 G-S, and a 60"LogRite!

Engineer

I specified a 4" slump, 4000 psi mix with peastone and plasticizer for my Reward ICF's.   Scott gave a very good post on concrete so I have not much to add to it.  I vibrated them with a squre of plywood and a rubber hammer.  As for foam, I used the Windlock foam but only on the bottom course and cuts.  Everything else just locked together with zip ties and rebar.

TexasTimbers

The ICF jobs I worked on we used foam on every block, every course.

Dave make sure to have plywood bandaids ready before you pour, in case you have a blowout with concrete that wet.
The oil is all in Texas, but the dipsticks are in D.C.

Dave Shepard

We already had the blowouts before this thread. ::) It was only a three course pour, so it shouldn't have been a problem, but our blockout method didn't work out so well. In the future, I'll probably use the Simpson joist hangers designed for Logix.
Wood-Mizer LT40HDD51-WR Wireless, Kubota L48, Honda Rincon 650, TJ208 G-S, and a 60"LogRite!

DouginUtah


How much horizontal rebar are you flatlanders using? Out here I have to use horizontal rebar in every course (16"). And verticals every 32".
-Doug
When you hang around with good people, good things happen. -Darrell Waltrip

There is no need to say 'unleaded regular gas'. It's all unleaded. Just say 'regular gas'. It's not the 70s anymore. (At least that's what my wife tells me.)

---

TexasTimbers

I use 3/4" out of the slab every 8", stubbed up 12", tied into the first horizontal, and then 1/2" Grade 40 verticals up from there every 24", and horizontals for every course. Verticals within 6" of all openings (windows/doors). This is for an 11" PolySteel form and no special circumstances..

This exceeds the PolySteel minimums of 1/2" grade 40 verticals every 48" and within 12" of openings. I try not to forget that ICFs are merely forms until the concrete hardens. A steel reinforced monolithic concrete wall inside an ICF form structure is just, a steel reinforced monolithic concrete wall if the ICF forms were to be removed. ;D

The forms make the lay person see more strength than is there just because they are so thick. But remember they are just styrofoam, soy-based, or whatever they are made of. They offer insulative benefits as to conduction resistance and mositure barriers after the crete dries but no added strength.

It is possible to put too much steel in a slab or wall and thereby weaken it, but I liked the spacing I was taught by my friend and now retired PolySteel rep. Now living in Florida near you I think Tom. Anyhow, 48" was too far apart in his opinion and I agree with him.

I've said this before but it bears repeating, I am not an ICF "expert" or guru, just have my opinions based on my limited experience so anyone reading this, use any info only as a umping off point to do your own research. That's good advice when reading the advice of any and all posters IMHO.

There are MANY variables when discussing any aspect of concrete. It is an extremely  complex subject and science, and any builder who tells you there's not much to it, my advice is to avoid his advice. :)
The oil is all in Texas, but the dipsticks are in D.C.

Engineer

In my town there's no code requirements so you do what the form company says, or what the engineer says.  In my case, being the engineer, I overdid the rebar a bit.  I have three walls with rebar at 16" oc horizontal and 32" oc vertical, and my back wall is full-height backfill so I did 2 bars every course horizontal and a #5 bar every 16" vertical.  I also designed my own concrete mix and had no blowouts, not even a bulge.  Probably luck more than anything else.  Reward says you don't need to foam every course; the zip ties were my idea.

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