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High time to put slag to good use

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Slag, a by-product of steel production, could be used in place of cement, and is of much superior quality when compared to traditional cement, writes NEMMANI SRIDHAR .

Steel is one of the chief ingredients in the manufacturing processes across a wide spectrum of industries.

For many, demand for this versatile metal is also a bellwether for forecasting the health of an economy. So needless to say, the production of steel is only set to increase as the demand for further goods increases.

With a healthy amount of iron ore available in the country, steel industry is only set to increase its foot print.

But there is one lacuna in this proposition.

Top quality

With increased steel production, the amount of slag (by-product produced while making steel) will also increase proportionally and a major portion of this slag is ending up in land fills, says construction material expert L.H. Rao.

On an average, about 70 million tonnes of steel is produced in the country along with about 20 tonnes of slag, he says.

“Only about 20 to 30 per cent of this slag is being used productively and rest is finding its way into landfills. Whereas this slag could be used to make slag cement which is much superior to the others,” he says.

The production of normal cement, Ordinary Portland Cement (OPC), follows the process of crushing limestone, heating it with coke and grinding the resultant clinker along with gypsum. In this whole process, carbon dioxide (CO2) is produced in large quantities of which the process of heating the limestone with coke alone produces 60 per cent of the total CO2 emitted.

Emission aspect

When slag is used in the making cement, this emission is reduced considerably.

According to the regulations, slag cement, also known as Portland Slag Cement (PSC), can have a composition of a maximum of 70 per cent slag and rest OPC. This means the emission of CO2 can be reduced by a huge margin, Dr. Rao says.

When compared to slag cement, the fly-ash based cement is not very effective in reducing the CO2 emission as fly-ash component can be a maximum of 35 per cent in the Pozzolana Portland Cement (fly-ash based blended cement).

There is a need for the government to take active steps to utilise the already available material and use it for creating recycled materials that can reduce the carbon footprint, he explains.

“The first step in developing environmentally sustainable procedures and technologies is to reduce our dependence on raw material and encouraging the use of recycled old concrete and utilising slag for making cement are some of the ways,” Dr. Rao maintains.

Low cement concrete technology is the latest trend being used in developed world and policy makers should look into this new technique so that correct construction procedures can be used, he says.

Greenhouse gases

Despite advances in technologies, people and builders tend to prefer OPC which depletes natural lime stock and increases green house gases. Government taking proactive role in promoting the blended cements like PPC and PSC along with other recycling processes is stressed.

“Most of the high grade iron ore in our country has already been exported so is the case with coal. The key in achieving sustainable development is to use the correct material in respective industry. This can be achieved only when government makes an inventory of the natural resources available in the country and allocating them effectively to the industries,” Dr. Rao maintains adding that authorities should also take note of the byproducts being produced by the industries.

“Low cement concrete technology is the latest trend in the developed world and policymakers should look into this new technique so that correct construction procedures can be used”


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