Mat Foundation Mass Concrete Design

[rlewistx]

I am working on the design of a 90'x60'x3' mat foundation and am looking for some recommendations for concrete parameters as it relates to mass concrete and construction detailing.

I'm considering one pour using type 2 cement, low w/c ratio, 3,000 psi strength. I believe I need to require insulation blankets to control differential concrete temperatures.

What other considerations should I make? Should I request thermocouples to monitor inside temperature? How long should the blankets be in place? I haven't seen any guidelines for that.

Thanks

 

[SlideRuleEra]

The mat foundation that you describe is not particularly massive - 3 ft. thick is not unusual. Type II cement is probably a good idea (for hot weather). Normal concrete placement techniques should work well. Maybe I'm missing something, but what is the purpose of the (cold weather?) insulation blankets? What differential concrete temperature?

http://www.SlideRuleEra.net

 

[Lutfi]

Consider slag in the mix (may be 50-50) it will reduce the heat of hydration.

As SlideRule mentioned 3 foot thick mat is not that massive. Curing is the big trick. I am old school and still like to use the jute blankets or mist spray. Curing concrete properly and taking care of it pays off big time in the long run.

Regards,



Lutfi

http://www.cdeco.com

 

[rlewistx]

I'm looking at PCA's "Design & Control of Concrete Mixtures". In the Mass Concrete section they state that when members approach 2-3 feet you should consider the "mass concrete" options.

They recommend thermal blankets to keep the exterior temperature from deviating from the interior temperature by more than 36 deg. F. This is to prevent thermal cracking during curing. I was wondering how long it should stay on.

 

[SlideRuleEra]

Althought I'm not familiar with that PCA book, I won't contest it; it has been around a long time. However if weather conditions are such that you are considering Type II cement, then "getting rid" of heat is probably a bigger concern than controlling the differential temperature that you describe. Insulating blankets will make heat dissipation more difficult. In hot weather, suggest that you don't thermal blankets at all. Continuous wet curing, as Lutfi mentioned, should be fine.

http://www.SlideRuleEra.net

 

[flamby]

3' is not so massive. If you are putting any rebars in it, they will take care of any heat difference. The heat of hydration does not crack concrete. It's temperature gradient that does the damage. In PCC, it might be an issue, but not with RCC. But I am not sure what you are doing.

Use of thermocouples or any devices is a comlpete waste, which give you only data, not control. If you are that concerned, use chilled concrete(<10 deg C) and use blankets during curing.

Ciao.

 

[rlewistx]

You state the concerns I have and say it's no big deal. I realize the temperature gradient is the problem, that why I asked about insulation. I assume that's the blankets you refer to. I guess the only difference between your response and my questions deals with whether I know what the temperature is in the concrete or not. If I know the temperature I can decide to add more insultation or remove some/all of it.

Are most redimix plants able to give chilled concrete?

 

[flamby]

Chilled concrete requires ice flakes. If you are close to any modestly industrial town, getting ice may not be problem for readymix plants.

I think PCA book gives the method to compute temperature rise. You will also need to contact cement manufacturers for calorific curve of cement.

One particular thing that is mostly heard in such applications is Fly-Ash concrete. I have never used it, but seen in promoted in big way.

Ciao.

 

[SlideRuleEra]

As flamby has stated, both ice and fly ash may be of help in hot weather, but they can only help so much.

Ice is great for keeping the concrete temperature down during placement (say for 90 minutes, or so). However it is of no value in controlling temperatures during curing.

Fly ash (included in Type IP cement) helps slow the heat generated during hydration, but Type II cement does the same thing.

During electric power plant construction (mass concrete, up to 18 feet thick) in SC we have had the opportunity to use plenty of both. On the hottest days, used just ice flakes, no (liquid) water at all in the concrete mix. Started using fly ash in concrete in the 1970's - (at that time its use was not common). My company, the electric utility, produced and sold fly ash as a waste byproduct of burning coal - we wanted to promote the use of fly ash.

http://www.SlideRuleEra.net

 

[craigory28]

I think the Type 2 and using Slag or Fly Ash will give you decent results as stated above.

I would require the supplier to provide a mix design they have used in the past for similar applications with all the breaks along with any other data they took on it. I would suggest having a conference before pouring with the concrete supplier and general contractor.

Craig