Concrete.... What did I do wrong?

[Circle C]

After taking great pains to make sure I had measured correctly, and prepared the base for a concrete pour, I still had problems with the volume of concrete required...   If there is anyone here that has experience with forming, calculating, and pouring concrete, I'd sure appreciate some feedback.



I used 2x4's for form boards, and sand for the base.  I was figuring on about 3" of concrete being used after some compaction of the base.

I started with the 2x4 forms, then back filled with sand, that 2.5" below the top of the 2x4. Now, this was an exact 2.5", I didn't guess, or eyeball it, I wetted and packed the sand and "screeded" with a 2.5" jig to make sure that I had a uniform base. I figured with the packed wet sand as a base, my compression would me minimal, so I guessed at 1/2".  Making the slab 3" of concrete.

Here is my math.

I had 3 footers that are 6" x 10' x 3" = .14 cu yd
        1 walkway that is 4' x 10' x 3" =  .37 cu yd
        1 walkway that is 30" x 24' x 3"= .56 cu yd
            total volume of concrete = 1.07 cu yd

I ordered a U-Cart concrete load of 1.25 yards, figuring I would have almost 20% extra in case something didn't go right.  The concrete yard says they had just calibrated their machine, so it should have been close to 1.25 cu yd....  However, when it came time to pour, I ended up not having enough to pour the footers, and had to mix sac-crete to get enough concrete to finish the job.  I ended up 10% short, when I figured on 20% over...

What gives?   Is my math wrong? should I have figured in more for compaction of the base? If so, how much more?   Did I get shorted on concrete?     

I have some more small projects coming up, and I would like to keep from running into this problem again, so any advice is appreciated.

[DangerZone]

4'x10'x.25'=10....10/9= 1.1 yd

[Circle C]

4'x10'x.25'=10....10/9= 1.1 yd

You just lost me...

[Cutter Bay Kennels]

Chris,

I always figure 80 square foot = 1 yard.  That is the typical calculation for a 4" slab.  I use 1"x4" 's as form boards.  It is always better to order .5 yards extra due to imperfections in your base, and any irregularities in your framing being square.  I figure .5 yard is $50, so it is money well spent.  Just browsing over your #'s, it looks ballpark, so I'm not certain what your issue was.  Did you place a moisuture barrier down first in your forms?  It certainly looks as though you did it as anyone else would have.   

[Circle C]

4'x10'x.25'=10....10/9= 1.1 yd

You just lost me...

The more I think about this figure, I think you are saying a 4' x 10' x 3" slab is 10 cu ft...which I agree with, but then you are dividing it by 9, shouldn't it be divided by 27?

[Circle C]

Chris,

I always figure 80 square foot = 1 yard.  That is the typical calculation for a 4" slab.  I use 1"x4" 's as form boards.  It is always better to order .5 yards extra due to imperfections in your base, and any irregularities in your framing being square.  I figure .5 yard is $50, so it is money well spent.  Just browsing over your #'s, it looks ballpark, so I'm not certain what your issue was.  Did you place a moisuture barrier down first in your forms?  It certainly looks as though you did it as anyone else would have.   

CBK,

     I did not put down a moisture barrier. Just poured over the packed sand.   I really thought ordering 20% extra would have been enough.  The other problem, is the UCart concrete only comes in trailers up to 1.25 cu yd.. I could have ordered a truck, but then I would have about a 3 or 4 yd min.    The frustrating part of this, is somewhere someone is off... either my math, my prep work, or the concrete guy.   If I had a 10 yard pour figured with these same calculations, and I figured an extra .5 yd, I'd still come up 2.5 yds short... that's how far off this job was.  30% best I can figure.

[DangerZone]

i'm wrong

[matt_aggie04]

I think you got fugged on the concrete.  There should have been plenty int hat ucart to pour what needed.

[Cutter Bay Kennels]

Chris,

I've seen your figures, but to make it real simple for guys like me that are not that smart, do you have any pics of what was poured after you poured it?  I'd like to see them.

[Circle C]

This is the only pic I have right now.  The rough looking stuff in the bottom of the pic is a pile of sand... I put a heavy broom finish on the poured concrete.

The long section is 30" x 24'
The other section at top left of pic is 48" x 10'
the three footers are 6" x 10'

[Bryant]

If your forms were correct, you should have had plenty of concrete.  Your math is correct.  I always figure 10% waste but you ordered more than that.

This is a pretty common problem we deal with all the time with batch plants.

I'm unfamiliar with the UCart your talking about, but look in the yellow pages in your area for a short-pour company.

[Cutter Bay Kennels]

This is the only pic I have right now.  The rough looking stuff in the bottom of the pic is a pile of sand... I put a heavy broom finish on the poured concrete.

The long section is 30" x 24'
The other section at top left of pic is 48" x 10'
the three footers are 6" x 10'

The picture helped.  I come up with 1.4375 yards of concrete needed based off of a typical 4" slab.  Supposing that your sand was slightly off in spots, that is the only difference I could see, as you were shooting for a 3" slab.  I think they cheated you on concrete.  I think I would invite the manager over to measure himself.  I think they can do a dog pen section on the house when you're ready for the mud.   

[tuskbuster]

their concrete wasnt right ,urs was correct ,tell they need to recalibrate their crap

[Rockin-P-Ranch]

their concrete wasnt right ,urs was correct ,tell they need to recalibrate their crap

X2 Chris

[DangerZone]

http://www.engineering.com/calculators/concrete_volume.htm

you got shorted,,,,,, I had the same ##s as you the first time i cal. it in inches,, then I brain farted it when I rechecked it in feet.

[Peachcreek]

Chris concrete is what I do for a living, As you know your math is correct. The problem comes from the ucart batch plants. They mix the concrete at somewhere around a nine inch slump because it is not being churned during transport and this keeps it from setting up to fast. The "mix" volume may have been 1.25 yrds at the plant but in this heat it does not take long for water to evaperate so by the time you got it placed you were dealing with less material. It is a fact that my yield is better during the cooler months and I think it is due to the added water to keep the concrete plastic during transport. I always figure 4% waste on my jobs and it seems like the smaller the job the more waste there is. I try not to use ucart unless it is just a strange job that i cant get a truck to. I would say you were shorted due to water or just straight up greed.

 L x W x H = cubic feet devided by 27 = cubic yards x 1.04 for waste

[dub]

I ain't smart enough but here is what I have used.

http://www.concretenetwork.com/concrete/howmuch/calculator.htm

[Circle C]

Peachcreek,

      The Ucart plant is about 10 minutes from my place, and there was about a 2" layer of water on top of the concrete when it got to the house. Mandi did the hauling, and they told her that they put extra water on top to help with the heat and to keep it from drying out in transport....    Does this sound kosher?     

FYI,  I am not looking to give the Ucart guy a hard time, and I probably won't bother contacting him, I just want to know what's up for future reference.    I do have a handful of projects coming up, and I may just go ahead and form out everything I need for all the projects, and have a truck come pour all of it. Rather than doing each job individually. But if for some reason, I can't do them all at once, I'd like to know how to plan accordingly...

[Peachcreek]

Peachcreek,

      The Ucart plant is about 10 minutes from my place, and there was about a 2" layer of water on top of the concrete when it got to the house. Mandi did the hauling, and they told her that they put extra water on top to help with the heat and to keep it from drying out in transport....    Does this sound kosher?     

FYI,  I am not looking to give the Ucart guy a hard time, and I probably won't bother contacting him, I just want to know what's up for future reference.    I do have a handful of projects coming up, and I may just go ahead and form out everything I need for all the projects, and have a truck come pour all of it. Rather than doing each job individually. But if for some reason, I can't do them all at once, I'd like to know how to plan accordingly...

sounds about like what i was talking about they use scales and water is figured in as volume. If you need a finisher or two for a day I would be more than happy to send you a couple good guys. If you pay their daily rate. PM me if ya need any help.

To me it is always better to get everything ready and make one pour, this is not always possible. It allows you to not waste as much concrete and pay for finishers one time.

[BobbyB]

When I worked for Zachry, my crew poured hundreds of yards as duct bank encasement.

In the mixer trucks, it is loaded by weight, not yards. And if the sand and gravel was wet, the load would be short on volume. If it was dry, we'd get a little more that what was ordered.

But I also found out right quick that any order under 3 yards tended to be short. and the less it was, the greater the shortage was. The concrete companies would argue with me all day, but when the ditch and the pipes is all exactly the same and I could pour say 10 yards over 65 feet and then a 10 yards truck only covered 50' of ditch, you tell me.


When I poured my kennel slab, I used a company that had a 5 yard truck and delivered on Saturdays. I had ordered extra and was still short about 3 wheel barrow loads. I jumped they guy and he told me that it was because I formed with 2 x 6's. I told him to go fork himself because I figured concrete all the time and I had figured the slab at 10 x 16 x .5 and I was shorted. There should have been enough to pours an apron across the front

I doubt they did it intentionally Chris, but I am betting you were shorted.