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Cold Weather Mix Specs

 
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Old 12-14-2009, 03:33 PM   #1
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Cold Weather Mix Specs


What % air do you suggest shooting for when working with cold weather concrete? I figured 5%-8%, but is that enough?

I'm planning on using a low slump mix with either a cold weather accelerator, or maybe Type III Cement. And thermal blankets for the curing process.

But i've got to provide specs to my testing company of about where I want my loads in terms of slump. So I'm shooting for a 2-5 in slump (shouldn't be hard to get that I think), but I don't want to mis-shoot the air test and have to fill out "Non Conformance Reports", and especially not have potential freezing damage on my concrete.
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Old 12-14-2009, 05:14 PM   #2
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Re: Cold Weather Mix Specs


Air is OK, but maybe 8% is a little high. It sounds like you may have a slab, but air is always good for any exposed concrete in a colder climate. Do not bother with any fly ash concrete, since the ash usually retards the strength gain.

The key is to have a good concrete supplier. If you have a good supplier, you can get warm concrete and using Type III is O.K. if you can place it fast enough. A good way to check suppliers is to see if the plant is certified and can supply DOT or municipal projects.

Warm (not hot) concrete acts just like normal concrete in the summer. The key is to protect/insulate it early. The longer the insulation is place, the faster the natural heat of hydration will assist in strength gain.

In critical situations, the cost of the material is really not important, since most of it is just material cost in a good automated plant with adequate aggregate storage and cement options.

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Old 01-11-2010, 07:22 PM   #3
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Re: Cold Weather Mix Specs


Quote:
Originally Posted by Southengineer View Post
What % air do you suggest shooting for when working with cold weather concrete? I figured 5%-8%, but is that enough?

I'm planning on using a low slump mix with either a cold weather accelerator, or maybe Type III Cement. And thermal blankets for the curing process.

But i've got to provide specs to my testing company of about where I want my loads in terms of slump. So I'm shooting for a 2-5 in slump (shouldn't be hard to get that I think), but I don't want to mis-shoot the air test and have to fill out "Non Conformance Reports", and especially not have potential freezing damage on my concrete.
Type III high early sets very fast, if u want to losten it up use a super plastisizer to get it to your desired slump, 5%-8% is good as long if that is between the spec of the contract, use a non chloride accelerator before calcium, i have poured many jobs with type III with 1% or 2% non chloride it goes very fast with hot water, better use 1% depending on the job at hand. With the air test, as long as the supplier has good material it should come out good, but not all the time, tell the cement supplier what u need, and tell them if it is too high at time of placement u might need to reject the load. If u take the air test after 20% discharge and the air is too high like 8.5% do not reject, remix for 5 min tell driver to stop drum completely, wait two min, retest, that will sometimes get air down, if air is two low the driver can add more air if he caries it. Make sure driver does not add too much water to mix before adding super, it will make air high, i would sugest a 3" slump and add just super to get to 5", but a 7" slump is acceptable with super without rejection, if driver make it too wet wait till slump decreases and retest, u have about one hour from batch to placement to pour the concrete, if u add retarder add 30 min., depending on your spec. Dot spec suppliers are a good way to go. I would shoot fo 6%-7.5%, but 8% is acceptable depending on the contract spec. All advice i gave is ohio odot and depends on contract spec.

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Old 01-11-2010, 07:27 PM   #4
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Re: Cold Weather Mix Specs


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Originally Posted by concretemasonry View Post
Air is OK, but maybe 8% is a little high. It sounds like you may have a slab, but air is always good for any exposed concrete in a colder climate. Do not bother with any fly ash concrete, since the ash usually retards the strength gain.

The key is to have a good concrete supplier. If you have a good supplier, you can get warm concrete and using Type III is O.K. if you can place it fast enough. A good way to check suppliers is to see if the plant is certified and can supply DOT or municipal projects.

Warm (not hot) concrete acts just like normal concrete in the summer. The key is to protect/insulate it early. The longer the insulation is place, the faster the natural heat of hydration will assist in strength gain.

In critical situations, the cost of the material is really not important, since most of it is just material cost in a good automated plant with adequate aggregate storage and cement options.
Good advice, i agree.
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