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+--- Thread: Diluting concrete with water to make it workable (/showthread.php?tid=13185)
RE: Diluting concrete with water to make it workable - Haaheo okole puka - 02-20-2014
quote:
Originally posted by Mtviewdude
General rule of thumb, you can add 1-2 gallons per cubic yard to increase the slump without it being too much of an issue. If I had to choose between 1-2 gallons -vs- poor slump, I would add the water, any more I would reject the batch.
However if you are curious, from the studies I have read.
Adding ~2.5 gallons per cubic yard reduces the strength ~25%
Adding ~5.0 gallons per cubic yard reduces the strength ~50%
Adding ~7.5 gallons per cubic yard reduces the strength ~75%
Hawaii concrete mixes (due to their aggregates) tend to be stronger then specified. On the 4k psi mix we ordered the cylinders were breaking at ~5.2k.
Usually on the batch form it will specify "max add water".
Nice... I didn't see that. It's been about 15 years since I worked out here (Kona side) professionally speaking. I recently ordered a minimum 3 yard (as I recall) 4k batch from the Pahoa yard. I used it for my cesspool lid. The lid is 12" thick but I had no problems screeding the top off after vibrating it. I would have needed additional water but could have added it topside if was after a smoother finish. It's nice to hear they are mixing above the cited test. Over hydrating out here has obviously been accounted for to some reasonable degree.
RE: Diluting concrete with water to make it workable - unknownjulie - 02-20-2014
If there is 4,000 psi concrete, why does anyone order any less?
RE: Diluting concrete with water to make it workable - Rob Tucker - 02-20-2014
Because lower strength concrete costs less money.
RE: Diluting concrete with water to make it workable - Seeb - 02-20-2014
The simple solution is to be hire an experienced and reputable crew
RE: Diluting concrete with water to make it workable - unknownjulie - 02-20-2014
Ah, yes, Seeb, but that costs money. I am doing things on a shoestring and that means I have to learn/supervise/figure out- stuff on my own... This forum is awesome for that! I'll be getting 4,000 psi concrete for sure. Thanks so much to everyone for the info!
RE: Diluting concrete with water to make it workable - Seeb - 02-20-2014
I have an old concrete apprentice book around here somewhere if you want to borrow.
RE: Diluting concrete with water to make it workable - Haaheo okole puka - 02-20-2014
That's a big task Julie and its one that's not forgiving. I would imagine within todays building environment you can find some experienced concrete people with tools who are willing to do side jobs for a reasonable cost.
Read about it and then run an add on Craigslist for a couple knowledgeable people that have the necessary tools on hand.
If you're doing a slab any larger than say 4'X8' hire some pros willing to do it on the side. A minimum order is 3 yards in Pahoa and I believe 4 yards in Hilo regardless of what you use. That's a pad in Hilo with 4 yards at 4" thick being 336sf. (less footing) 4x8 is only 32sf...
Pros will make it look easy but I can assure it's not if you've no prior hands on experience. Not even the form work is simple around here, not in this lava. You'll need to work fast and hard during a pour, there's no time for breaks or questions, pedicures, etc and the concrete drivers time is more money beyond X time limit. If you're doing some basic footings (cant imagine you'll need much concrete though), give her a go. If it's a foundation, don't even try it without a pro involved.
Also the mixers chute is only so long and if every place needed to pour is not readily accessible by truck and its short chute, you'll need a pumper truck too and those hoses are damn heavy and the pumper truck is additional money. Most the time a boom pump is used and those are real expensive. You're very likely in for a whole lot of surprises going it alone. The logistics alone are a big factor in concrete.
RE: Diluting concrete with water to make it workable - Haaheo okole puka - 02-20-2014
Come to think of it, if you're pouring under a house that's up on jacks... you'll need a pumper truck with hose along with the concrete truck. Who's going to drag that hose around and guide the pour? Who's going to vibrate and who's going to work the grade and finish? That's a minimum 3-5 man crew with know-how experience.
RE: Diluting concrete with water to make it workable - DanielP - 02-21-2014
At a concrete seminar that I attended years ago, we were urged to use very little vibrating, as this tended to move the large aggregate down lower into the slab, thus creating weakness. Plasticizers may be ordered in the mix to make it more workable without adding water. Also, highly emphasized, was to let the bleed water escape (evaporate and percolate downward*) before floating and finishing. and never add water, after the slab is placed, except as a fine mist, to slow excessive evaporation. Do not trowel water down into the finish burn.
* If plastic sheeting is used under the slab, it should be used under a layer of compacted base course, to allow the bleed water to escape uniformly by evaporation and percolation.
When vibrating, use quick stabs and move along, so as not to allow the large aggregate to liquify and sink to the bottom.
RE: Diluting concrete with water to make it workable - unknownjulie - 02-21-2014
I am hiring someone to do it, but since he is cheap there is always more risk involved. It is a fairly small pour- but the site prep is the hardest part, and I'll be there eyeballing the entire thing. I am having someone build all the forms. There will be more people here when the truck actually arrives. I agree this is a hugely complicated job and it is very stressful to consider all the pieces involved to make it work out. I do not want to do it, but the piers are sitting on rocks and are not stable. I can put my hand underneith them. The support beams are dryrotted and termite gouged. It has to be done, and it could cost a fortune to "hire a highly successful contractor". I just have to do the research ahead of time, have a good plan- and then pray.