EFFECT OF SOME CONCRETE ADMIXTURES ON THE SILICA FUME BLENDED CEMENT PASTES

Abstract

Producing blended cements, namely pozzolanic and blastfurance slag cements has been of considerable scientific and technological interest because such addition increases the chemical resistivity to salt attack of the fanned cements. The use of these blended cements is increasing world wide because these cements need less energy for production and reduce cost.

The effect of substitution of condensed silica fume on the properties of the blended cement pastes was investigated. The silica fume-blended cements were prepared by mixing 10, 20 and 30% by weight of cement. The hydration of these blended cements was compared with that of corresponding Portland cement pastes. Water of consistency, initial and final setting times were determined. The rate of hydration was followed by the determination of free lime, chemically combined water, free lime contents, bulk density/total porosity and compressive strength during the hydration of the hardened cement pastes. It is clear that, as the silica fume content increases the water of consistency. Initial setting time accelerates by addition of 10% condensed silica fume, but it elongated the final setting time. As the silica fume increases the setting time is elongated. In blended cement pastes, as the hydration proceeds, the free lime

content decreases with curing time as well as the content of silica fume increases. The chemically combined water content increases with curing time for all cement pastes.