Use Of Fly-Ash In The Cement Industry For Environmental Sustainability

Cement is among the most commonly used building materials, second only to water in terms of global use. Without question, the rock-solid material underpins much of modern society. However, with there being a pressing need for manufacturing industries to go through a green revolution, the time is right for construction and allied industries to fast-track adoption of green technologies for manufacturing low-carbon products, such as using fly-ash for producing blended low carbon-cements, as well as reducing their own carbon footprint.

Research by leading Indian cement industry players exemplify the effects of fly-ash based cements/concretes. The material is already used in commercial concrete and its applications are only expanding. Work is underway to update fly-ash standards for faster adoption by the cement industry so that the concrete products it produces last for decades. In this regard, collaboration between cement producers and large-scale fly-ash producers, such as the aluminium industry, will go a long way in establishing win-win solutions for both. Aluminium producers like Vedanta have frequently sought partnerships with the Indian cement industry for utilizing their fly-ash in gainful ways.

India is an emerging economy where large-scale construction projects are perennially underway. Around 576 kg CO2 is produced for every tonne of cement produced in India. While the average specific thermal energy consumption and average specific electrical energy consumption of Indian cement industry are lower than the world average due to commendable energy conservation efforts.

by the domestic players, the GHG emissions of the industry as a whole is high owing to process emissions. And hence, the demand for increasingly environmentally sustainable practices from the cement industry, is not a new one.

(Source: Alliance for an Energy Efficient Economy)

The Levers For Accelerating Transition To Net Zero Emissions
The direct CO2 intensity of cement production increased 1.8% per year during 2015-2020. In contrast, 3% annual declines to 2030 are necessary to get on track with the net zero emissions by 2050 scenario.

(Source: International Energy Agency)

According to a report published by the International Energy Agency (IEA) and World Business Council for Sustainable Development (WBCSD), the three main levers that can support sustainable transition of the cement industry are improving energy efficiency (which is already being done by the industry), switching to low-carbon/renewable fuels and energy sources (which is also being done, but are dependent on a variety of market factors such as availability, prices, etc.), integrating carbon capture into cement production (a very nascent technology world over) and finally, reducing clinker-to-cement ratio. The last lever has the second highest emission reduction potential at 37%, since it reduces process emissions which cannot be addressed by energy efficiency measures.

The basic process of calcination, which is essential for manufacturing cement, is responsible for nearly half of the CO2 emissions in the industry and has been one of the main reasons why lowering emissions is difficult. The reduction of clinker in cement production reduces the quantum of thermal energy required for producing cement, which results in CO2 emissions savings. India has been a pioneer in the manufacturing of blended cements, using calcined clay, mixes of calcined clay and fly-ash, fly-ash and granulated blast furnace slags. Of these, usage of fly-ash for blending has been a win-win scenario on grounds of environmental sustainability, as it is already an industrial by-product, and widely available in a thermal-power reliant country like India.

Merits Of Using Fly-Ash In Cement Production
An important factor here is to ensure that the virtues of blended cements are supplemented by the performance criteria of composite cements, thereby resulting in better end-product quality. The advantages of using fly-ash with slag for blending offers multiple benefits in terms of water consumption, workability, better mechanical properties and durability.

In fresh concrete, fly-ash reduces water demand in concrete, increases workability and pump-ability, bleeding and doesn’t affect setting time. In hardened concrete, in the later stages, it increases the compression strength compared to OPC, while the long-term shrinkage and creep is similar or lower than OPC concrete of same grade. Fly-ash also reduces water and chloride permeability at later stages, increases protection of reinforcement if well cured, and substantially increases resistance to sulphate attack.

(Source: Sustainability and Blended Cements)

Portland cement may be combined with up to 40–50% fly ash for specific purposes, such as where quick setting time is not necessary, decreasing emissions by nearly the same amount while lowering cost. Fly ash not only aids in the manufacturing process, but it also aids in the durability of concrete. Extending the life of a material decreases emissions and energy consumption when it is used to repair or replace a structure. To ensure good performance, researchers are systematically evaluating the range of chemical and physical properties that fly ash must have, as well as the extent to which it can be mixed with Portland cement. With a 30 – 33% blending ratio, fly ash can help save 270 kg of carbon emissions for every tonne of cement produced.

A Collaboration In Waste-To-Wealth
Companies like Vedanta Limited’s Aluminium business, whose aluminium smelters are powered by mammoth thermal power operations, are the right circular-economy partners for cement producers. Usage of high-quality coal at their captive power plants, generates low-sulphur good quality ash, which is perfect for cement production, brick manufacturing, road and infrastructure industries. In fact, the company has been supplying fly-ash free of cost over the last 4 years to players in cement, road, brick and infrastructure.

India’s per capita cement consumption at 240 kg is well below the global average of 530 kg, which signifies immense opportunities and at the same time portends significant increase in carbon footprint. To get on track with the sustainable development scenario, a 0.8% annual decline in CO2 intensity to 2030 from global cement industry is necessary. A two-way focus on reducing clinker-to-cement ratio (including through greater uptake of blended cements) and deploying innovative technologies (such as Carbon Capture Units) is necessary in this scenario. This also calls for collaboration between the government, cement industry and fly-ash producing industries for investing in R&D and encouraging adoption of green methodologies, to ensure that better quality of life for people does not come at the cost of the environment.

For further information,
info.wastetowealth@vedanta.co.in