STRENGTH PROPERTIES OF CALCINED KAOLIN AND SILICA FUME AS PARTIAL REPLACEMENT OF CEMENT

Silica fume (SF) is a byproduct of the smelting process in the silicon and ferrosilicon industry. The reduction of highpurity quartz to silicon at temperatures up to 2,000°C produces SiO2 vapors, which oxidizes and condense in the low temperature zone to tiny particles consisting of non-crystalline silica. By-products of the production of silicon metal and the ferrosilicon alloys having silicon contents of 75% or more contain 85?95% non-crystalline silica. The byproduct of the production of ferrosilicon alloy having 50% silicon has much lower silica content and is less pozzolanic. Therefore, SiO2 content of the silica fume is related to the type of alloy being produced . Silica fume is also known as micro silica, condensed silica fume, volatilzed silica or silica dust. The American concrete institute (ACI) defines silica fume as a ‘‘very fine noncrystalline silica produced in electric arc furnaces as a byproduct of production of elemental silicon or alloys containing silicon’’. It is usually a grey colored powder, somewhat similar to Portland cement or some fly ashes. It can exhibit both pozzolanic and cementitious properties.