Fly ash is the major alternative material used at Nuvoco plants
Sanjay Joshi, Chief Manufacturing Officer, Nuvoco Vistas.

Fly ash is the major alternative material used at Nuvoco plants

Though government agencies are regularly updating the guidelines for the usage of alternative materials in manufacturing cement, there is a need for a tracking system that can balance the generation, demand, and supply equilibrium, feels Sanjay Joshi, Chief Manufacturing Officer, Nuvoco Vistas.

Usage of supplementary cementing materials by cement plants is increasing due to various advantages it offers. What are your thoughts on this?

Alternative material or supplementary cementing materials like fly ash and slag are often added to concrete to make the mixtures more economical, reduce permeability, increase strength, or influence other concrete properties.

These materials replace clinkers in cement grinding that is manufactured in cement plants through the pyro process. Pyro process involves heating of limestone powder up to a temperature of 1,400 degree Celsius and then cooling it to 100 degree Celsius. This entire process involves energy-consuming activities. Given the increasing prices of fuel and electricity, usage of alternative materials significantly reduces energy consumption.

Fly ash is the most widely used pozzolanic material in concrete. It is a by-product of thermal power generating stations. As per the properties of concrete made through Portland pozzolana cement, fly ash addition to cement is restricted by up to 35 per cent by the Bureau of Indian Standards (BIS).

Granulated blast-furnace slag is a glassy, granular material formed when molten, iron blast-furnace slag is rapidly chilled - typically by water sprays or immersion in water. Concretes made with slag cement will usually exhibit higher compressive strengths, better durability and lower permeability compared to Portland cement concrete. As per BIS, the limit for slag addition to making cement is up to 70 per cent.

After various studies conducted by laboratories, it was found that fly ash and slag can increase strength, reduce permeability, and improve the durability of the concrete from the aspects of the alkali-aggregate reaction, sulfate-resistance, and reduced heat of hydration.

More importantly, SCMs can lead to a significant reduction of the carbon footprint of concrete, and hence, are essential to achieve sustainability.

Please explain in detail how materials like slag or fly ash is been utilised at your plants and in what proportion?

All plants in Nuvoco are using fly ash as the major alternative material to produce Portland Pozzolana Cement. It is sourced from the market through a direct pipeline where thermal power plants are nearby and through closed bulkers from far-situated power plants. Fly ash once received at the plant is evacuated from bulkers and stored in large silos, from where it is directly fed to cement grinding mills through weighing scales.

Slag is sourced through railway wagons from steel manufacturing plants. It is then stored in silos and fed to roller press/vertical roller mills for grinding it to a fine powder, which is then blended with OPC to produce slag cement.

Almost every plant of Nuvoco is using fly ash in the range of 33 to 34.5 per cent, while eastern plants are using slag in the range of 58 to 62 per cent. Studies are going on to further increase slag addition in our eastern units.

From where do you get these supplementary materials? Is transportation of SCMs a challenge in India? Have you partnered with any companies/agencies for supply and logistics?

Fly ash is generated in thermal power plants as a result of the combustion of pulverised coal. We get fly ash from power generating thermal power stations situated near our cement plants. Slag is generated in steel plants and is mostly sourced in East India from suppliers like Tata Steel and Jindal Steel.

Yes, transportation is one of the biggest challenges as we are dealing with very fine materials that can fly away if kept open. Fly ash is transported in closed bulkers, which are emptied out through pneumatic systems. Slag is transported by means of tippers, dumpers and railway wagons.

We have a long-term agreement with some of the big generators of fly ash and slag near our cement manufacturing units in eastern and northern India.

On an average, 35 per cent of fly ash remains unutilised. How do you look at this problem in India? What can be done to meet this challenge?

Currently, almost all thermal power stations in the country are selling fly ash to different cement plants for consumption. The unutilised fly ash can be further consumed in the cement or concrete manufacturing process after conducting lab test trials for more than 35 per cent addition of fly ash in cement, which is the current BIS limit.

We can also encourage the usage of fly ash bricks in the housing sector.

Relaxations in the limit of fly ash addition i.e. 35 per cent to Portland pozzolana cement will also result in higher consumption.

With affordable housing, infrastructure development is on the focus of Budget 2021, how do you look at the demand for alternative materials like fly ash?

As per the Budget FY21 announcements, the government has shifted emphasis to infrastructure development in the country. These actions will definitely enhance the demand for alternative materials like fly ash and slag. The usage of fly ash and slag-based cement will increase in the housing sector.

Do you think we lack in monitoring regime of the utilisation of fly ash/slag? Is there a need for proper enforcement of monitoring regulations?

Government agencies like MOEF and CPCB are regularly updating the guidelines for the usage of alternative materials in manufacturing cement. But still, there is a need for a tracking system that can balance the generation, demand and supply equilibrium. The increasing demand for fly ash and slag in cement plants has resulted in an increase in their prices. A tracking system will also help in keeping an eye on the pricing of these commodities.

What are your future plans in terms of the utilisation of supplementary cement materials at your organisation?

Nuvoco product portfolio includes 80 per cent blended cement which means fly ash-based and slag-based. We will continue to produce blended cement and consume fly ash and slag as key alternative materials for cement manufacturing.

What are your thoughts and initiatives in lowering the carbon footprint/emission rate in the cement industry? What solutions do you have in place for the same?

The cement industry is one of the world’s biggest industries and the second-largest contributor to greenhouse gas emissions. The chemical and thermal combustion processes involved in the cement manufacturing process are a large source of carbon dioxide (CO2) emissions.

The clinker manufacturing process is a carbon-intensive process because of the carbon released by limestone (CACO3) and the energy (electrical and thermal) required in the process. Therefore, CO2 emissions may be reduced by replacing clinker per cent in cement with waste materials like blast furnace slag and coal ash.

To reduce carbon footprint, operational advances, such as energy-efficiency measures, have largely been implemented, and the emissions-reduction potentials are being explored by using more and more alternative fuels.

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