Slab-on-grade Concrete 2

[jike]

What do I need to specify to achievwe a concrete slab on grade with minimal slab curling, a low shrinkage potential and have a finished surface with a low moisture content for quick application of a moisture sensitive finish material?

Maximum water cement ratio?
A water reducing admixture?
Use of the largest possible large aggregate size = t/?
Curing?

 

[DaveFlax]

You just described concrete made with Type-K Shrinkage-Compensating cement. Instead of shrinking, the concrete will actually expand. Spacing between joints of 150 feet and more without sawcuts and without cracks is common. Because the concrete expands rather than shrinks, it tries to curl up in the middle instead of at the edges, but it can't do that so it just stays flat. w/c=.45 Because Type-K cement needs .45 w/c to hydrate, all the water is tied up and there is little to no bleed. Seven days of water cure are required, but moisture sensitive finishes can usually be applied 10 to 14 days after placement. ACI 223 covers all this very nicely.

 

[jike]

I have used Type K, years ago, for a slab-on-grade foods warehouse. I am not sure what current costs are.

Can what I am describing be accomplished with normal cement? This is the typical problem for a commercial grade office building with moisture sensitive finish floor and a vapor (barrier) retarder.

 

[SlideRuleEra]

jike - This article should answer most of your questions
ftp://imgs.ebuild.com/woc/C02I021.pdf

Here are a couple of other, also
ftp://imgs.ebuild.com/woc/C02A079.pdf
ftp://imgs.ebuild.com/woc/C01I050.pdf

 

[DaveFlax]

A newer refinement to type-K in the last couple years allows slabs to be placed without steel reinforcement. The only reinforcement at all are the little plastic fibers that are incorporated with the cement. The fibers are not there to keep the concrete from shrinking. The Type-K Shrinkage-Compensating cement does that. The fibers are there to prevent the concrete from expanding too much. This system adds $30 to $35 to a cubic yard of concrete, but the savings from rebar cost, rebar placement, sawcutting, joint filling, increased productivity, etc. etc save much more than that and the system ends up saving on initial costs. And ongoing maintenance costs are reduced as well. You can get reduced shrinkage and curling using portland cement as pointed out in the excellent articles from Slide Rule Era, but it will cost you a little more for the concrete. The only way to reduce shinkage and curling to zero or near zero that I know of is Type-K concrete and it saves you money and allows quicker installation of moisture sensitive flooring besides.

 

[Ron]

Type K is a bit difficult to get in some areas and expensive. Use the parameters you have outlined, using the largest practical aggregate size you can get, preferably 1-1/2" nominal, keep the cement content as low as you can and still achieve strength and durability, and wet cure it.

 

[DaveFlax]

As long as the job is in the US, the Type-K Cement is easy to get as long as there is some lead time. I have found that 4 weeks is more than sufficient. As to cost: Type-K cement does cost a lot more than portland cement. If all the savings from sawcutting, joint filling, etc are taken into account Type-K concrete costs about the same or slightly more than portland concrete. However, if the System-K is used and rebars are eliminated (we all know what has happened to steel prices lately) then the savings from using Type-K concrete are tremendous.