Microsilica vs Flyash
Microsilica vs Flyash
(OP)
Which is superior in terms of
performance/cost?
Does anybody have bad experiences with flyash cement?
performance/cost?
Does anybody have bad experiences with flyash cement?
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RE: Microsilica vs Flyash
Microsilica is very expensive, adding up to $50/cy. It isn't that common, so batch plants don't like to deal with it. It is ultrafine, so it's hard to handle. It is used to greatly increase the strength and/or density of concrete.
Unless you have a special need, I would stay away from microsilica. Fly ash, on the other hand, makes a cheaper and easier to handle mix.
RE: Microsilica vs Flyash
RE: Microsilica vs Flyash
RE: Microsilica vs Flyash
RE: Microsilica vs Flyash
The big advantage of silica fume is the very high strengths, but it requires a lot of water. One pound of silica fume has over 2 acres of surface area that must be wetted. It is sticky and it is hard to keep it from shrinking and cracking.
The big advantage of fly ash is it lowers the cost of the concrete and, because fly ash is basically small spheres, it assists in both finishing and pumping. The drawback is that it delays strength gains so early strengths will be lower.
RE: Microsilica vs Flyash
Microsilica is more used for protection of the rebar. As Daveflax said it is 100th the size of a cement grain and so the concrete matrix is less permeable than OPC or the one mixed with fly ash. Micro silica does need a lot of water in the mixing and the high performance superplasticers have been developed to solve this problem. Microsilica needs water for curing as well and finish is generally superior to OPC.
As far as I am aware the French Charles de Gaulle airport is mixed with it and finsih quality is presented as an architectural feature.
Apart from better protection to the rebar, higher strength (though not usually the prime motivation behind as a bit of more cement can achieve the same result) microsilica is one of the rare material one can add to the mix to improve the abrasion resistance of the concrete. Thus it is popular in areas where water flow at velocity too high for the normal concrete.
RE: Microsilica vs Flyash