Silica Fume As A Strength Enhancer in Low Density Slurries

Silica fume is a pozzolanic material composed of extremely fine, amorphous spheres produced as a by-product in the manufacture of silicon metals. It has a high water demand and is more reactive than natural pozzolan or fly ash. When added to cement it makes an excellent extender and produces significant increases in compressive strengths. This paper examines the compressive strengths of low density slurries made with different blends of Portland cement, fly ash, and silica fume. Both Class C and Class H slurries, mixed at 11.5 ppg to 13.0 ppg, and cured at temperatures ranging from 80 to 170 degrees F were tested. These compressive strengths are compared with the strengths of conventional slurries extended with anhydrous sodium metasilicate or bentonite to the same density. The results show that silica fume is beneficial as a strength enhancer at low densities over a range of temperatures