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. Silica fume and fly ash different performance : Silica fume has higher compressive strength than the fly ash. Silica fume also has significant advantage over fly ash when permeability is a factor.
Silica fume is more used for protection of the rebar. It is residue left from burning coal, which is collected on an electrostatic precipitator or in a bag house. It mixes with flue gases that result when powdered coal is used to produce electric power. Class C is produced from lignite or sub bituminous coal. In Canada, there is a further distinction. When the lime content is percent, it is classified Cl, and when it is higher, it is class C. Silica Fume is typically much more reactive, particularly at early ages , because of its higher silicon dioxide content and because of its very small particle size.
A correlation was found between the mass of the dissolved material and the calcium content of the liquid. Open PDF. Magazine of Concrete Research. Volume 49 Issue , December , pp. Authors: N. De Belie. Search for articles by this author. Author Affiliations. Key: Open access content Subscribed content Free content Trial content.
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