Effect of Water-Cementitious Ratio on the Compressive Strength of Silica Fume Concrete

Abstract

Silica fume is obtained by the reaction of high purity quartz with coal in electric arc fumacei in the production of ferro- silicon alloys. Because of extreme fineness and pozzolanic property the reaction is most effeclive with the hydration product of portland cement in concrete. Silica fume is a mineral admixiure added in cement as a partial replacement for cement to improve certain properties of concrete and mortar in addition to savings in cost of the material. High strength concretes are achieved by reduc ing water-cement ratio and by using high range water reducing admixtures. In the present investigation an at tempt is made to achieve high strength concrete using silica fume. The maximum density principle states that ihe reduction in voids content of hardened concrete increases the strength. This reduction of voids in the hardened concrete can be achieved to a maximum extent by using well-graded aggregates with the maximum size of 20 mm (for normal mixes). The continuous grading curves are chosen to ensure this. The strength of fully compacted concrete depends mainly upon the w-c ratio. But the grading of aggregate affects the workability, which in turn affecls the water and cement requirement. A mix can be more workable, but at the cost of segregation. It is easier to pack particles of different sizes together as the smaller particles have a tendency to come out easily during vibration. The voids in the combined aggregate should also be sufficiently small to prevent cement paste from passing through and separating out. For a mix to be satisfactorily workable, it must contain sufficient amount of fine materials. The cement particles come under this fine material. A richer mix requires a lower conlent of fine sand than for a lean mix. If the sand is deficient in finer particles, only increasing'the fines/coarse ratio may not be satisfactory and rnay lead to harshness. The aim of the present investigaiion is to study the effect of water-cemen titious ratio on the compressive strength of concrete keep ing workabilit5r constant and maintaining coarse to fine aggregate ratio as 1.85.