Fly Ash In Structural Concrete
Fly Ash In Structural Concrete
(OP)
My question is whether anyone can give me some history on the use of fly ash in structural concrete. As an office standard, we do not allow the use of fly ash according to our specifications. I have never really been given a satisfactory answer as to why that is the case. I was wondering if anyone else does not allow fly ash in your mix designs and why. If you do allow it, maybe you could tell me why you do so as well. Thanks for any information.






RE: Fly Ash In Structural Concrete
-Mike
RE: Fly Ash In Structural Concrete
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I would trust PCA for engineering questions on it;
http://www.cement.org/
When things are steep, remember to stay level-headed.
-Horace
RE: Fly Ash In Structural Concrete
Fol
Dik
RE: Fly Ash In Structural Concrete
Concrete with fly ash sets and gains strength more slowly than the same mix without fly ash. It will reach the same final strength, however - just takes longer. In hot weather slowing down hydration is an advantage, not as much heat generated. In colder weather, fly ash is a disadvantage, it takes what seems to be "forever" for the concrete to cure.
Fly ash is included in Type IP Cement.
www.SlideRuleEra.net
RE: Fly Ash In Structural Concrete
Codes recognize this substitution and consider fly ash to be part of the cementitious material in the mix as it does hydrate and impart strength to the concrete, albeit slower in gain as stated. When you read or hear the term water-cement ratio, it is really water-cementitious material ratio which might include fly ash, ground blast furnace slag cement, or other materials having a pozzolanic effect.
With appropriate consideration and fitting to the application, there is no reason fly ash shouldn't be allowed in certain concretes.
RE: Fly Ash In Structural Concrete
Alten
RE: Fly Ash In Structural Concrete
RE: Fly Ash In Structural Concrete
There is a color difference between regular concrete and fly ash concrete. This is the reason stated by architects for not using fly ash concrete for exposed concrete. Apparently the archtiects really like gray. Slag is also starting to be introduced for regular use in my area. It has not caught on as of yet.
RE: Fly Ash In Structural Concrete
RE: Fly Ash In Structural Concrete
RE: Fly Ash In Structural Concrete
RE: Fly Ash In Structural Concrete
RE: Fly Ash In Structural Concrete
RE: Fly Ash In Structural Concrete
The cement mfr said that they do not see the same problem with ground granulated blast furnace slag. Since they get the slag from a blast furnace there is less variablity because of the tighter controls on what goes into a blast furnace versus burning of coal.
For these reasons, our preference is to allow slag in the mix.
RE: Fly Ash In Structural Concrete
RE: Fly Ash In Structural Concrete
RE: Fly Ash In Structural Concrete
We do not allow Type F since this has created problems with air content. We allow only Type C.
We use it as a 1:1 substitute for cement up to 20%. As Ron said you need to measure "water to cement + flyash" ratio since fly ash is considered cementatious material.
Retardation of set time for flatwork is a problem.
RE: Fly Ash In Structural Concrete
I agree with the beneficial aspects of fly ash. Slag also has many similar benefits.
RE: Fly Ash In Structural Concrete