Pouring High Strength Concrete

bobbrown

I am used to pouring 3000 or 4000. need to do a job that requires 6500.
Are there any differences I should be aware of? This is a slab situation.
Interested in set up time, workability time, slump, vibrating, etc.

Thanks
bob

stacker

my only experince with 6500# concrete,was years ago.i didnt pour it,but it was on a wal mart remodel job.the super for the firm doing the remodel flucked up and ordered 6500# instead of 3500#.this was in early july in nw oklahoma so it was hot.the man finishing the concrete was a friend of mine and he does good work,but the concrete was setting up before he could do squat to it.it turned out to be the god awfullest job i have ever seen.which was not the finishers fault.he had no idea he was pouring 6500 until after most of the load was poured.

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concretemasonry

Work with the concrete supplier that is required to supply the 6500 psi mix. Your job is to make sure it performs as expected. Get some suggestions and help! If they are a good supplier, they know more about high strength concrete and placement than most contractors.

Around here, high strengths for slabs are usually related to durability, since adding thickness is cheap. Some suppliers here require 4000 or 4500 psi for a duability guarantee.

With high strengths, there are many ways to acheive the result of 6500 psi. these include super plasticizers, which fool the concrete (and the contractor) into thinking there is more water in the mix than there is.

Pay attention to the weather (temperature, humidity and wind) to anticipate how fast things will go.

With high cement contents, you need to have extra manpower available if the concrete starts to get away from you. You never have a second chance.

Since you have an unusually high compressive strength requirement, you should look a little further into the specifications and any additional placement requirements.

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Dik Redi

OUCH i feel for your buddy(( lotta of sleepless nights if he has heart into biz ) on that job that is

joasis

The rapid set up can lead to failure of the slab from cracking also....it has been my experience to get the saw cuts done as quick as possible, then wet to cool.

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masonking02

wouldnt hi strenght concrete be prone to cracking??

JustaFramer

I would think about wet curing that slab for five to ten days.

What is the sq footage of the slab,thickness,and what is being used rebar or mesh?

Considering what time of the year it is there is probably no need for calcium or hot water.

6stringmason

The concrete I use for countertops is fairly high strength. Usually around 6500 or higher with all the admixtures I put in. Using a super plasticizer can make it alot more workable, but also makes it stronger since you're using less water. It also depends on what type of cement their using. I generally use type III.

I dont have problems with cracking, but Im not doing slabs either.

I guess I really had nothing to add lol

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bobbrown

thanks for all the replys. due to the potential problems we have now gone to 4000 w/ added depth.
All the replys helped alot...thanks