Industrial slag seen ideal for construction

Ashok B Sharma

New Delhi, Aug 26: THE waste can be converted into wealth. This concept is fast becoming a reality. Microsilica and silica fume, the wastes of the ferro-silicon and zirconium industries can now be extensively used in building high strength and durable concrete structures in the country.

The ultra-fine strength and durability of microsilica and silica fumes has already been assessed by the engineers and technical staff of the Union ministry of water resources and they have concluded that these industrial wastes can be used to give strength and durability to sensitive structures like spillway or overflow structure of dams, stilling basins or plunge pools, power houses, multi-storeyed buildings and long span bridges.

The latest code on plain and reinforced concrete brought out by the Bureau of Indian Standards (BIS) has already incorporated these materials under mineral admixtures. Ordinary Portland cement requires a good quality limestone. Several surveys have stated quality limestone reserve in the country may not last more than the next 30 to 40 years in our country. Therefore, time has come to seriously consider some of the partial Portland cement replacement materials like flyash, silica fumes and slag.

But there is no precise data on the annual output of the silica fume in the world partly because of the proprietary nature of the alloy industry. In India, too, the output data on micro silica and silica fumes are not available. In such a situation, the Union ministry of water resources is planning to import these materials after working out cost benefit ratio on account of such imports.

Microsilica and silica fumes are relatively newer materials for construction activity than compared to other wastes put to use like slag and flyash. The initial interest in the use of silica fume was mainly caused by the strict enforcement of air pollution control measures in various countries to stop release of the material into the atmosphere during the production of elemental silicon and alloys containing silicon in electrical arc furnaces.

The potential use of silica fume was initially limited but with the advent of high range water reducing admixtures, new possibilities for the use of silica fume as a part replacement material for cement in the concrete to produce very high strength or very high levels of durability or both have opened up. Initial researches done in Scandanavian countries like Iceland, Norway and Sweden way back in 1960s has lead to other countries to follow suit and silica fume has come to be accepted as a partial replacement for cement in concrete worldwide for the past few decades.

India has also begun using silica fumes in water resources structures in a limited way. In Srisailam project in Andhra Pradesh, erosion and cavitation problems have occurred in the stilling basin area for which silica fume based underwater cement grouting is being adopted.