Silica fume is a by-product from electric arc furnaces used in the manufacture of silicon metal of silicon alloys. The material, which contains more than 80% silica in the form of extremely fine particles (0.1 Âµm average diameter). When used to produce high-performance concrete, silica fume is typically 4-15% of the cement weight. The exact addition rate depends on the specific performance characteristic to be improved. Compared to the other ingredients in concrete, the amount of silica used is small.
The use of pozzolanic materials is an old as that of the art of concrete construction. It was recognized long time age, that the suitable pozzolona used in appropriate amount, modify certain properties of fresh and hardened mortars and concretes.
Pozzolanic materials are siliceous or siliceous and aluminous materials, which in themselves possess little or no cementitious value, but will, in finely divided form and in the presence of moisture, chemically react with calcium hydroxide liberated on hydration, at ordinary temperature, to form compounds, possessing cementitious properties.
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