Hi
I am building a small adition, (basically replacing a enclosed porch with an actual addition with basement.) I formed and poured the walls and footings, and had the concrete trucked in by regular sized truck. It was only 5 yards for the walls. Since the new basement floor is so small, I arranged for a mini truck delivery, actually, a pick-up with a smaall mixer on a trailer. The delivery charge for a small load from the regular truck was more than the cost of the concrete. now, here is my problem. The floor measured 6′ 3″ by 16′ 2″ and I wanted a thickness of 3″ Acording to my calcuations, this is .9 yards, or just under three quarters of a meter. They brought me a meter, but it only did about two thirds of the floor, and I had to get another load, and used about half a meter more, according to the driver. (I had to pay for two full meters) Again, if I calculate backwards from what they gave me and the floor dimensions, the floor should be over 6″ thick, which it is not.
I feel that I calculated correctly. Other jobs I have done turned out correct. I feel that the mini truck suplier shorted me the corect amount in the mixer. The drum was heavily coated in set concrete.
Do they load the mixers by weight, or by actual volume at the plant. Any thoughts on what I can do to claim back some money? Or did I really goof on the calculations?
Thanks for any comments
Stemreno
Replies
FWIW, I calculate 0.72 cubic meter.
I've thought about using the new, local 'mix at site' truck for a small job I am planning. I'll be interested to see how your situation resolves itself. One of the concerns I have is how you know they are metering accurately.
In my job, it's a 5x9 porch on top of a concrete block wall, and I want to fill the block cores - which seems difficult to accurately estimate.
Edited 8/10/2007 10:44 am ET by woodturner9
Metered truck are notorious for being innaccurate around here. Coarse, fine aggregate and cement are loaded in hopper bins on the truck. Mix ratios are determined by gate sttings on the hoppers, then water is added after the dry mix is mixed and as it it is augered down the shute. From my experience with them the only measurable is the metering of the water, making a wet mix meter out to more actual yards than it acctually is. Makes for a hell of an argument with the driver and dispatcher when you have to pay for more concrete than you know can fit in your form. BTDT. If you keep the mix dry you get closer to your calculated usage.
The only time I have won the battle with a metered concrete supplier is when I have taken pictures of the formed flat work, with appropriate screed and folding rules shown, before the pour. Show them to the driver before the pour and stay on them about the water they add.
QC on batch strength is another issue. If you want to really get thier shorts in a knot take some test cyclinders.
Dave
Metered truck are notorious for being innaccurate around here. Coarse, fine aggregate and cement are loaded in hopper bins on the truck. Mix ratios are determined by gate sttings on the hoppers, then water is added after the dry mix is mixed and as it it is augered down the shute. From my experience with them the only measurable is the metering of the water, making a wet mix meter out to more actual yards than it acctually is. Makes for a hell of an argument with the driver and dispatcher when you have to pay for more concrete than you know can fit in your form. BTDT. If you keep the mix dry you get closer to your calculated usage.
That sounds like what we have here. Until about a year ago, only conventional readymix was available - and none of the sites are close to me. So I get concrete that is "only" 45 minutes old, if I am lucky. When I did the garage floor 27' x 16', the finisher was working so fast it was like a blur - and there are still a couple of spots that set before he could finish it well.
Initial conversation suggests that the meter truck is a good bit more expensive than readymix, but for this small job I'm not sure what else to do. I'm not sure how to calculate the block fill with any degree of accuracy - it's the older tricore block, and I'm not sure how much I will be able to get to actually go into the cores. I do have other "small" jobs, such as the drive apron, but I need to pour the garage apron/pad first, and I'm nowhere near ready to do that. The porch is cracked and leaking now, so it needs to be done.
Here is a question - for a smaller job like this - 5'x9', call it 15 cu ft, .55 yard, 23 bags would you use ready mix, meter truck, or mix the bags? The block cores could add another 1.9 yard (estimating 19' of wall x 8' high *8/12 for 8" block, divided by 2 to estimate the cores), but probably less, maybe a lot less. If it's really 2.5 yard, that'd getting close to the 5 yard minimum for ready mix around here. Is there a better option?
I'm not familar with tri-core blocks, so this is just a guess. On standard 8x16x8 hollow core block i calculate exterior demensions and then reduce the volume by 20%. fo your block with more webs, I would reduce by 30%.
For slushing block I order concrete with pea gravel as the dense aggregate and then add a super plastizer on sight to get a temporary lower slump while placing the mix. If the pour is part of another pour, such as flat work, I make sure I pour the walls last. I don't want the finishers waiting on me while I mess around with a tediouse and time consuming block wall fill, and I don't want then dealing with a hot mix either.
I have never used an add mix on a metered mix job. Don't know if the option is even available.
For the small price differance and your "close to minimum size pour, I would just pay the min. and get it from a batch plant. With a 45 minute haul time, tell the load dispatcher you want a retarder added at the plant. You might get a little more wiggle room for placing and finishing that way
Dave.
Yeah, I make it out to be 0.715 cubic meters. Maybe their meters are after taxes.
However, how sure you of the 3 inch number? If you didn't carefully smooth and compact the floor, it's easy to be off by an inch or two on thickness from what you're figuring.
Hi.
I hope this post is going to all, not sure how to do that in a reply.I can guarantee that there is 3" thickness in my floor. Here in Canada, it was a long weekend, and the plumbing inspector made me wait from thus to Tues for his weeping tile inspection. I had a long time to set and level the gravel, and mark the height on the walls. But even if I wasn't accurate, the amount of concrete they claim they delivered would have resulted in 6.5" thick floor, and that is defineatly not the case
The driver wanted to add water to the mix, but I thought it was good right out of the drum, it was easy to work and finished nicely, and hardened enough to walk on in 45 mins. I'm not an expert in this, but to me that seemed ideal.
Was the floor fairly well packed before pouring? Remember, the weight of the concrete will compress it somewhat.Also, if pouring over coarse gravel, the gravel will "absorb" a certain amount of concrete.(To reply to "ALL", click on the pull-down next to "To:" on the message editing screen and select "ALL" (generally the second or third option) from the list.)
So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
The gravel was very hard packed, I was joking with my guy that all we had to do is add water and trowel it smooth. The gravel was actually crushed concrete that was left behind when the concrete truck filled the forms for the walls. He cleaned out his truck into the foundation hole, and left me his extra. I had to goto the loo and didn't catch him until too late. We had to break it up with a rotary hammer and used it for the fill inside. It packed very well, roughly 1/2" chunks after we had done.
I really think the mini truck shorted me. It's not a lot of money, but 300 here, 300 there and it adds up. I would like to get the second delivery charge back, but kinda doubt it.
Thanks for all the comments
Stemreno
Your math is correct (.935 yds or .71 cu mtrs).
The most likely scenerios:
1. Your slab is over 3" thick
2. Your concrete delivery was short.
3. Forgot to account for the curvature of the earth.
So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
A yard of concrete is ample for what you were pouring. You ordered that much concrete and they didn't come through. They need to be taken to task!
Those of us who are outspoken and strong enough to do this help those who do not have the whateveryouwannacallit and make for a better environment for the building process which should and can be a cool thing to do!