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Concrete With Fly Ash Vs. Concrete Without?

 
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Old 03-31-2010, 08:34 PM   #1
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Concrete With Fly Ash Vs. Concrete Without?


What is your opinions on using concrete with fly ash and using concrete without it?

The reason I am asking is, we have for quite some time, used ready mix suppliers who use the fly ash (at around 15% ratio I think.) But, we have recently (last couple of months) been using a ready mix supplier who does not use fly ash, straight cement only, or so we are told.

The non-fly ash supplier's concrete definitely gets harder faster. But we have been having some problems of late with the finishing characteristics of the mud. Separation seems to be the greatest issue we have. My guys are complaining about not be able to float and trowel as easily.

The fly ash including suppliers concrete certainly finishes better, but does not seem to be near as good of a final product.

I'm not joking, you can't hardly drive a concrete nail in the non fly ash concrete the next day.

Any thoughts?
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Old 03-31-2010, 08:41 PM   #2
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Re: Concrete With Fly Ash Vs. Concrete Without?


I believe you.

It's the same with the C4 concrete mix. It is stickier and is therefore harder to work with. And it gets harder faster.

I wonder what the numbers are. For example, if you require 4000 psi concrete, why pay for 6000?

I suppose it all boils down to economics.

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Old 03-31-2010, 09:17 PM   #3
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Re: Concrete With Fly Ash Vs. Concrete Without?


The straight concrete mix will always cure faster than a mix with fly ash in it, but the ultimate strength will be about the same. Just don't pour a big slab in cold weather with a fly ash mix if you expect to finish it the same day. - I have seem some long hours or a second crew waiting most of the night on a big indoor slab in an unheated building. Some ended up being torn out because of the low temperatures of the aggregates or the base under the slab that dropped the temperature below critical levels when the cement reaction was too slow.

Fly ash is now not the "junk" or by- product that was used as a low cost cement replacement years ago. The good fly ash distributors have the supplies tied up for years and do the testing and carefully control the properties. Some cement is also made with fly ash as a raw material in the process.
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Old 04-01-2010, 03:03 PM   #4
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Re: Concrete With Fly Ash Vs. Concrete Without?


Quote:
Originally Posted by cdkyle View Post
What is your opinions on using concrete with fly ash and using concrete without it?

The reason I am asking is, we have for quite some time, used ready mix suppliers who use the fly ash (at around 15% ratio I think.) But, we have recently (last couple of months) been using a ready mix supplier who does not use fly ash, straight cement only, or so we are told.

The non-fly ash supplier's concrete definitely gets harder faster. But we have been having some problems of late with the finishing characteristics of the mud. Separation seems to be the greatest issue we have. My guys are complaining about not be able to float and trowel as easily.

The fly ash including suppliers concrete certainly finishes better, but does not seem to be near as good of a final product.

I'm not joking, you can't hardly drive a concrete nail in the non fly ash concrete the next day.

Any thoughts?
What mix are you using? (6sac,6 1/2 , 7, 800lb ms) I think concrete without fly ash finishes better. Fly ash reduces the heat in concrete. Seperation, sound like you are finishing your concrete when there is high winds, that will create some seperation, also are you using a slag mix?
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Old 04-01-2010, 09:22 PM   #5
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Re: Concrete With Fly Ash Vs. Concrete Without?


Most here use 5 1/2 sack mix.
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Old 04-09-2010, 10:06 PM   #6
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Re: Concrete With Fly Ash Vs. Concrete Without?


I agree with all said as mentioned , flyash is basically a filler , but in recent years mix designs have broaden massively , specific everything, what conditions are you pouring in ?? wet / dry / windy ?? maybe try wetting the base just prior to pouring . are you using any surface retarders? Maybe your supplier has chnged something in the mix ?
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Old 04-13-2010, 06:47 AM   #7
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Re: Concrete With Fly Ash Vs. Concrete Without?


Mixes with flyash take longer to make initial set however they finish much better.
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Old 04-13-2010, 07:08 AM   #8
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Re: Concrete With Fly Ash Vs. Concrete Without?


Chance are we are all going to get better acquainted with concrete containing no fly ash in the future

http://enr.ecnext.com/coms2/article_...FlyAshAsbest-1
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Old 04-13-2010, 01:27 PM   #9
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Re: Concrete With Fly Ash Vs. Concrete Without?


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Originally Posted by Anti-wingnut View Post
Chance are we are all going to get better acquainted with concrete containing no fly ash in the future

http://enr.ecnext.com/coms2/article_...FlyAshAsbest-1
I read that on another site yesterday; now when you click on it they want a subscription to read it.
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Old 07-19-2010, 04:18 PM   #10
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Re: Concrete With Fly Ash Vs. Concrete Without?


Check out this link:

http://www.newsok.com/article/3476858
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Old 07-19-2010, 07:58 PM   #11
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Re: Concrete With Fly Ash Vs. Concrete Without?


We recently poured a water disapator(sp) for the irrigation district and it was spec'd for 25% flyash due to the alkalinity of the water that runs through it.
And we noticed the set time for sure. So we actually had to have them ad high early for the 2nd and 3rd pours.
Never thought I would add high early during 80 deg weather.
As far as flat work finishing I did notice the fly ash mix has a nicer cream come up when floating..
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Old 07-19-2010, 09:34 PM   #12
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Re: Concrete With Fly Ash Vs. Concrete Without?


The reason it can make a smoother finish that can be easier or slower to finish is that they act like little round "marbles" in the mix. Ash can improve some of the chemical properties, but should be certified and tested to know what they are since there is good and bad ash around, but the good ash is under contract for years in advance by the larger distrubutors.
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Old 07-25-2010, 12:34 PM   #13
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Re: Concrete With Fly Ash Vs. Concrete Without?


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Most here use 5 1/2 sack mix.
When I came to Texas, I discovered that most here were using a slury mix of 3 sack .. .. scary stuff indeed.

The guys at the batch plant think I'm nuts, but the least I've ever ordered here was 5 (at a 4 slump) .. added fly ash by percentage for those really hot days and a J20 cure for the final ..

The only separation issues I've seen down here involved juiced 3 sack (too much water) and no fly ash
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Old 07-25-2010, 01:31 PM   #14
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Re: Concrete With Fly Ash Vs. Concrete Without?


A 3 bag mix on a slab would disappear over one winter or so here - No mater what magic stuff was added.

Around here, it is hard to get anything less than 4000 psi and 5-7% air and 3-4" slump delivered for a driveway. If you demand less, you may not get it or at least have to sign a waiver eliminating the suppliers liability for all problems. - Not enough profit in a volume of a driveway if you have failures for any number of different reasons.
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Old 07-25-2010, 01:53 PM   #15
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Re: Concrete With Fly Ash Vs. Concrete Without?


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A 3 bag mix on a slab would disappear over one winter or so here - No mater what magic stuff was added.

Around here, it is hard to get anything less than 4000 psi and 5-7% air and 3-4" slump delivered for a driveway. If you demand less, you may not get it or at least have to sign a waiver eliminating the suppliers liability for all problems. - Not enough profit in a volume of a driveway if you have failures for any number of different reasons.
I discovered all of this when I signed on to sub a job with a builder from Florida last year. My eyes popped out of my head when I saw the ticket and I turned 4 of the trucks around thinking the mix design was a mistake.

I learned after that, that the 3 sack slurry was the default around here, unless otherwise specified. I've only ever used slurry as a base at best on jobs with poor ground .. never as a main for any finished product.

At any rate, with the exception of Knife River, I get my 5 1/2 sack mix whenever I place an order these days around here from the others w/out asking specifically for it. Anything that resides on City/County property gets a 6 1/2 sack mix, even though it isn't really required by coding, just like how we do in North Central Montana.
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Old 07-26-2010, 05:39 AM   #16
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Re: Concrete With Fly Ash Vs. Concrete Without?


Using a 3 sack mix vs. a 5 sack mix is probably saving the ready mix company $10 - $15 per yard.

Question is, are they passing that savings on to the buyer?

But, who would willing and knowingly use a 3 sack mix?

I wonder what psi a 3 sack mix would attain?
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Old 07-28-2010, 08:37 PM   #17
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Re: Concrete With Fly Ash Vs. Concrete Without?


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Originally Posted by cdkyle View Post
Using a 3 sack mix vs. a 5 sack mix is probably saving the ready mix company $10 - $15 per yard.

Question is, are they passing that savings on to the buyer?

But, who would willing and knowingly use a 3 sack mix?

I wonder what psi a 3 sack mix would attain?
Absolutely not .. my price is 83 bucks a yard, 3 sack or 5 ..

um .. Transit Mix .. Knife River (Southeast Texas) ..

My guess would be (I haven't done the math lately), roughly 1500 to 1800 PSI and that's about it .. the stuff drills like sandstone, and wears about the same too.
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Old 07-28-2010, 08:51 PM   #18
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Re: Concrete With Fly Ash Vs. Concrete Without?


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Absolutely not .. my price is 83 bucks a yard, 3 sack or 5 ..

um .. Transit Mix .. Knife River (Southeast Texas) ..

My guess would be (I haven't done the math lately), roughly 1500 to 1800 PSI and that's about it .. the stuff drills like sandstone, and wears about the same too.
Around here we call that "lean" concrete and we use it for things like mudsills and filling dirt seams in weathered rock under footings where rock bearing is specified.

No way we would pay full price for "lean"
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Old 07-28-2010, 09:33 PM   #19
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Re: Concrete With Fly Ash Vs. Concrete Without?


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Around here we call that "lean" concrete and we use it for things like mudsills and filling dirt seams in weathered rock under footings where rock bearing is specified.

No way we would pay full price for "lean"
It's like I said in the previous post .. slurry being what it is, is only really used for poor ground .. but the Texans around here use it like it's the real deal for all of their finish jobs.

Quote:
I've only ever used slurry as a base at best on jobs with poor ground .. never as a main for any finished product.
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Old 07-28-2010, 09:57 PM   #20
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Re: Concrete With Fly Ash Vs. Concrete Without?


Cement is not the biggest cost in the delivered price of concrete. - It is just one item like different aggregates, admixtures/fly ash, but one of the biggest costs is delivery (time, distance and yds per load) because of the truck cost, fuel cost and clean-out/EPA costs.

If there is a lot of concrete used in an area the price (for the same profit) of higher strength concrete could be the sames as low strength concrete. - Especially if the job site time is higher for higher for the higher strength concrete, since time can be longer. - Just like pricing a job.

The ma & pa days of owners just marking up products based on material costs are gone.

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