Supplementary cementitious materials are changing the way and the speed at which cement manufacturing is moving on the spectrum of environment sustainability. With large stakes on the line for achieving net zero targets, how is the Indian cement industry rising up to the challenge, finds out ICR.
Across the globe, cement is one of the most consumed and important materials for building all infrastructure. From homes, to factories, roadways or tunnels, everything would require cement in one form or the other. India especially is moving towards becoming infrastructurally strong with new projects in the works across the sub-continent. All infrastructural projects demand the consumption of concrete and cement, which has led to the rise of concrete requirement, thus, increasing the production of cement.
India is the second largest producer of cement. Limestone is at the core of its production as it is the prime raw material used for production. The process of making cement involves extraction of this limestone from its quarries, crushing and processing it at the cement plant under extreme temperatures for calcination to form what is called a clinker (a mixture of raw materials like limestone, silica, iron ore, fly ash etc.). This clinker is then cooled down and is ground to a fine powder and mixed with gypsum or other additives to make the final product, cement.
Limestone is a sedimentary rock composed typically of calcium carbonate (calcite) or the double carbonate of calcium and magnesium (dolomite). It is commonly composed of tiny fossils, shell fragments and other fossilised debris. This sediment is usually available in grey, but it may also be white, yellow or brown. It is a soft rock and is easily scratched. It will effervesce readily in any common acid. This naturally occurring deposit, when used in large volumes for the cement making process is also depleting from the environment. Its extraction is the cause of dust pollution as well as some erosion in the nearby areas.
The process of calcination while manufacturing cement is the major contributor to carbon emission in the environment. This gives rise to the need of using alternative raw materials to the cement making process. The industry is advancing in its production swiftly to meet the needs of development happening across the nation.
Aligning Sustainability Goals
In one of its recent bulletins, owing to India’s announcement at the Glasgow Climate summit to reach net-zero by 2070, the RBI noted that with India aiming to reach half of its energy requirements from renewables and reduce the economy’s carbon intensity by 45 per cent by 2030, it ‘necessitates a policy relook across sectors, especially where carbon emission is high’ and ‘cement industry is one of them.’ However, it said, recent developments in green technologies, particularly related to reverse calcination, offer ‘exciting opportunities’ for the cement sector.
The RBI report noted that India’s cement production is expected to reach 381 million tonnes by 2021-22 while the consumption is likely to be around 379 million tonnes, in the light of the country’s renewed focus on big infrastructure projects like the National Infrastructure Pipeline, low-cost housing (Pradhan Mantri Awas Yojana), and the government’s push for the Smart Cities mission is likely to drive demand for the cement in future. On similar lines, according to the Eco-Business news portal report of April 2022, the India Energy Outlook 2021, which notes that most of the buildings that will exist in India in 2040 are yet to be built. Their projection suggests that urbanisation in the near future will demand an increase in infrastructure, which will ultimately lead to increase in the cement consumption.
With these forecasts in mind, RBI has recommended that there is a need to align India’s economic goal with its climate commitments by implementing emerging green tech solutions. It has also recommended an increase in finance towards green sustainable solutions through subsidised interest loans, proactive engagement with the leading research institutes and countries involved with green tech-related innovation in the cement industry.
“When clinker is blended with other supplementary cementitious materials like fly ash, slag or both, products are called Portland Pozzolana Cement (PPC), Portland Slag Cement (PSC) and composite cement (CC) respectively. Blended cement products have a much lower carbon footprint than OPC. Since clinker manufacturing is the phase where most thermal energy is consumed and CO2 is emitted, reducing clinker factor in cement not only results in lowering the process CO2 but also the thermal energy and electrical energy requirements,’’ says Manoj Kumar Rustagi, Chief Sustainability and Innovation Office (CSIO), JSW Cement.
Alternative Raw Materials
Alternative cementitious materials are finely divided materials that replace or supplement the use of portland cement. Their use reduces the cost and/or improves one or more technical properties of concrete. These materials include fly ash, ground granulated blast furnace slag, condensed silica fume, limestone dust, cement kiln dust, and natural or manufactured pozzolans.
“Each material has its own composition and behaves differently during the burning process. In order to maintain the consistent clinker quality and stable clinkerisation process, we need to analyse these materials with respect to quality (during raw mix design) and also impact on the environment (if any harmful gases are released). There are certain materials which come in both ARM and cement additives like Ashes from coal fired thermal plants and slag from steel plants that have to be looked at from various angles,” says Gulshan Bajaj, Vice President (Technical), HeidelbergCement India.
The use of these cementitious materials in blended cements offers advantages such as increased cement plant capacity, reduced fuel consumption, lower greenhouse gas emissions, control of alkali-silica reactivity, or improved durability. These advantages vary with the type of alternative cementitious material.
Cement manufacturers are moving towards incorporating these supplementary cementitious materials in their raw material:
Fly Ash: Containing a substantial amount of silicone dioxide and calcium oxide, fly ash is a fine, light, glassy residue generated during ground or powdered coal combustion.
Ground Granulated Blast-furnace Slag (GGBS): It is a by-product of the iron and steel industry. In the blast furnace, slag floats to the top of the iron and is removed. GGBS is produced through quenching the molten slag in water and then grinding it into a fine powder. Chemically it is similar to, but less reactive than, Portland cement.
Silica Fume: It is a by-product from the manufacture of silicon. It is an extremely fine powder (as fine as smoke) and therefore it is used in concrete production in either a densified or slurry form.
Slag: It is a by-product of the production of iron and steel in blast furnaces. The benefits of the partial substitution of slag for cement are improved durability, reduction of life-cycle costs, lower maintenance costs, and greater concrete sustainability. The molten slag is cooled in water and then ground into a fine powder.
Limestone Fines: These can be added in a proportion of 6 to 10 per cent as a constituent to produce cement. The advantages of using these fines are reduced energy consumption and reduced CO2 emissions.
Gypsum: A useful binding material, commonly known as the Plaster of Paris (POP), it requires a temperature of about 150OC to convert itself into a binding material. Retarded plaster of Paris can be used on its own or mixed with up to three parts of clean, sharp sand. Hydrated lime can be added to increase its strength and water resistance.
Cement Kiln Dust: Kilns are the location where clinkerisation takes place. It leaves behind dust that contains raw feed, partially calcined feed and clinker dust, free lime, alkali sulphate salts, and other volatile compounds. After the alkalis are removed, the cement kiln dust can be blended with clinker to produce acceptable cement.
Pozzolanas: These materials are not necessarily cementitious. However, they can combine chemically with lime in the presence of water to form a strong cementing material. They can include – volcanic ash, power station fly ash, burnt clays, ash from burnt plant materials or siliceous earth materials.
Dr Sujit Ghosh, Executive Director – New Product and R&D, Dalmia Cement (Bharat), says, “Blended cements made using supplementary raw materials, have ‘additional’ activated silica (SiO2) and/or activated lime (CaO), which when co-processed with cement clinker, provide ‘additional’ cementitious gel paste (complex calcium-silica-oxide-hydrates) when mixed with water, that renders improved strength and durability to the cement-concrete structure.”
He adds, “With specialised processing and with the use of performance enhancers, blended cements using supplementary raw materials, provide acceptable rate of strength gains, comparable to pure-clinker cement and top-class long-term durability, with lower carbon footprints and at the same time effectively finding value-solution to other industry wastes!”
Besides having the advantage of lower emissions and better environmental conditions, use of supplementary cementitious materials also has a cost benefit. “Cost of production depends on the plant location, limestone and raw material quality. The source of alternative raw materials for some plants are significant and in some instances because of high logistic cost economics do not work out. For example, if a cement plant is located near the industry where chemical gypsum is generated, there will be a significant gain to that particular cement plant,” says Rajpal Singh Shekhawat Senior General Manager (Production and QC), JK Lakshmi Cement.
Researchers at the Indian Institute of Technology, Madras, are finding ways to use bacteria to develop bio-friendly cement and reduce carbon dioxide emission, as per a report in The Hindu earlier this year.
Professor GK Suraishkumar and assistant professor Nirav Bhatt in the Department of Biotechnology and Subasree Sridhar, a research scholar, are conducting the research. They have developed a mathematical model to produce an alternative to current cementation process. They have suggested the use of bacteria like S Pasteurii, which will microbially-induced calcite precipitation.
This bio cement will require temperatures in the range of 30 to 40 degrees as opposed to the traditional process that would require over 900 degrees for the calcination process. The emitted carbon dioxide will be negligible in this case and industrial waste like lactose mother liquor and corn steep liquor can be used as the raw materials for the bacteria, thus making the manufacturing of this cement more economical.
One of the most important ways of reducing carbon emission in cement manufacturing is the use of alternative raw materials from various other industries. This gives way to a circular economy, utilising waste from other industries and bettering the environment with reduced emission of harmful gases, especially carbon dioxide. It also helps the avoidance of landfills or ocean pollution, as waste of industries is utilised in manufacturing cement. Overall, new compositions of cement are the future.
ICR explores the various facets around the integration of Supplementary Cementitious Materials (SCMs) into the cement manufacturing process, which has emerged as a crucial solution to enhance cost-effectiveness and environmental sustainability, resulting in effective management of issues such as carbon emissions and resource usage.
India is the second largest producer of cement in the world. Limestone is at the core of its production as it is the prime raw material used for production. The process of making cement involves extraction of this limestone from its quarries, crushing and processing it at the cement plant under extreme temperatures for calcination to form what is called a clinker (a mixture of raw materials like limestone, silica, iron ore, fly ash etc.). This clinker is then cooled down and is ground to a fine powder and mixed with gypsum or other additives to make the final product – cement. The reason we are elucidating the cement production process is to look at how supplementary cementitious materials (SCM) can be incorporated into it to make the process not only more cost effective but also environmentally responsible.
Limestone is a sedimentary rock composed typically of calcium carbonate (calcite) or the double carbonate of calcium and magnesium (dolomite). It is commonly composed of tiny fossils, shell fragments and other fossilised debris. This sediment is usually available in grey colour, but it may also be white, yellow or brown. It is a soft rock and is easily scratched. It will effervesce readily in any common acid. This naturally occurring deposit, when used in
large volumes for the cement making process is also depleting from the environment. Its extraction is the cause of dust pollution as well as some erosion in the nearby areas.
The process of calcination while manufacturing cement is the major contributor to carbon emission in the environment. This gives rise to the need of using alternative raw materials to the cement making process. The industry is advancing in its production swiftly to meet the needs of development happening across the nation.
Ratings agency Crisil forecasts an all-Indian cement consumption growth of 11 per cent year-on-year to 440Mt during the current financial year. Crisil attributed this to a 51 per cent year-on-year rise in infrastructure spending, to US$ 6.75 billion throughout the year.
Strong expansion of the industrial sector, which has fully recovered from the COVID-19 pandemic shock, is one of the main demand drivers for the cement industry. As a result, there is a strong potential for an increase in the long-term demand for the cement industry. Some of the recent initiatives, such as the development of 98 smart cities, are expected to significantly boost the sector.
Aided by suitable governmental foreign policies, several foreign players such as Lafarge-Holcim, Heidelberg Cement and Vicat have invested in the country in the recent past. A significant factor, which aids the growth of this sector, is the ready availability of raw materials for making cement, such as limestone and coal.
According to Indian Brand Equity Foundation (IBEF), cement demand in India is exhibiting a CAGR of 5.65 per cent between 2016-22. Nearly 32 per cent of India’s cement production capacity is based in South India, 20 per cent in North India, 13 per cent in Central, 15 per cent in West India, and the remaining 20 per cent is based in East India. India’s cement production is expected to increase at a CAGR of 5.65 per cent between FY16-22, driven by demands in roads, urban infrastructure and commercial real estate. India’s cement production was expected to range between 380-390 million tonnes in FY23, a growth rate of 8 to 9 per cent y-o-y.
Between FY12 and FY23, the installed capacity grew by 61 per cent to 570 MT from 353 in FY22. The Indian cement sector’s capacity is expected to expand at a compound annual growth rate (CAGR) of 4 to 5 per cent over the four-year period up to the end of FY27. It would thus begin the 2028 financial year at 715-725 MT/ year in installed capacity.
Sameer Bharadwaj, Head – Manufacturing Excellence, JK Cement, says, “The key feature of SCMs is their Pozzolanic properties, which refers to its capability to react with calcium hydroxide (CH) to form calcium silicate hydrate (C-S-H). Likewise, with the increased conventional fuel prices, adopting green energy utilisation is now become a necessity in order to bring down the cement manufacturing cost, in a similar manner adoption of SCMs to a larger extent is a must requirement in order to bring down the clinker factor because clinker manufacturing will anyhow emit carbon emissions for calcination of limestone, but what we as a sustainable oriented manufacturer can contribute toward less carbon emissions is to produce more blended cement with less requirement of clinker.”
“At JK Cement, we manufacture various types of blended cements in which the contribution of SCM is well within the BIS norms. Major SCM’s are fly ash and slag which are procured from nearby thermal power plants and steel industries. We produce PPC (fly ash based) at all our manufacturing units in which 35 per cent (maximum) fly ash is being utilised. Also, to promote the more usage of blended cement, we are producing premium category PPC Cement which has a compressive strength equivalent to OPC. In our Muddapur plant in the South of India, we are also producing Portland Slag Cement (PSC),” he adds.
“The production of SCMs require less energy as compared to traditional cement and support in reducing carbon emission and use of fossil fuels to combat environmental challenges like depleting natural resources, climate change and air pollution. The other advantage of using SCM is enhancing the durability of concrete. Mixing SCMs can make concrete long-lasting and efficient, promoting conservation of resources. By using durable concrete with SCMs during construction of green buildings, it becomes possible to reduce the need for frequent repairs, replacements, and extend the lifespan of buildings. For instance, materials such as fly ash and slag carry the potential to mitigate alkali-silica reactions which often lead to formation of cracks in buildings and impact concrete’s durability.
By incorporating SCMs, it becomes possible to avoid the damaging effects and achieve stronger and structurally sound buildings with longer lifespans,” says Arun Shukla, President and Director, JK Lakshmi Cement.
Dr SB Hegde, Professor Jain University, India and Visiting Professor, Penn State University, United States of America says, “The use of SCMs in cement production is primarily to reduce carbon emissions. This can result in tax incentives and compliance benefits, further improving the overall profitability of cement manufacturing. Let us take a hypothetical example of an Indian cement plant with an annual production capacity of one
“SCMs like fly ash, in the case of Wonder Cement, are actually an industrial waste product, which if left unattended, can cause nuisance for the environment. Our cement plant consumes this industrial waste and in turn also preserves the natural resources of limestone and coal which would be used as a raw material and as a source of energy for the manufacturing of cement,” says RS Kabra, Executive Vice President – Commercial, Wonder Cement.
According to a report by McKinsey titled Cementing Your Lead: The Cement Industry in the Net-Zero Transition, October 2023, alternative cementitious materials, such as low-carbon cement or geopolymer concrete, have historically struggled to scale. However, current investment trends and rapid technological advancements have allowed start-ups to disrupt the alternative-cementitious space with low-carbon offerings. For example, Brimstone replaces limestone in traditional cement production with calcium-silicate rock, and Sublime Systems uses an electrochemical process that eliminates the need for a kiln. Although these approaches are novel, investment data indicates that appetite for alternative cementitious materials is high: Brimstone announced a $55 million funding round in 2022, and Sublime Systems has raised more than $40 million in two funding rounds since 2021.
In particular, supplementary cementitious materials (SCMs) offer promising ways to significantly reduce the carbon footprint of traditional cement and concrete. Traditional SCMs—such as fly ash, ground granulated blast-furnace slag (GGBFS), and silica fume—can be used to partially replace the clinker used in cement or the cement content used in concrete. This can have both sustainability and cost benefits, but SCMs are typically not fully leveraged.
In many markets, local and regional standards limit the volume of traditional SCMs in cement based on their hydraulic and cementitious properties. For example, the European Union limits fly ash to a maximum of 35 percent, whereas the United States limits it to 40 percent. New SCMs such as calcined clay, limestone, and recycled concrete may require a reevaluation of these standards to maximise both the performance and decarbonisation potential of cement and concrete, particularly as the availability of traditional SCMs decreases.
Exploring Long Term Benefits of SCMs
SCMs are materials that can be used in cement manufacturing to partially replace traditional Portland cement clinker, thereby reducing the environmental impact of cement production. The incorporation of SCMs in cement helps reduce the carbon footprint, energy consumption and natural resource usage associated with cement production.
Some of the most used SCMs are:
• Fly ash is a fine, powdery byproduct of coal combustion in power plants. It is rich in silica and alumina and is often used as an SCM in cement production. When properly processed and blended, fly ash can improve concrete workability, reduce heat of hydration, and enhance long-term durability.
• Blast furnace slag is a byproduct of iron production and consists of glassy granules with latent hydraulic properties. Ground granulated blast furnace slag (GGBFS) is commonly used as an SCM in cement to improve concrete properties and reduce the heat of hydration.
• Silica fume is a very fine, amorphous silicon dioxide powder obtained from the production of silicon and ferrosilicon alloys. It is highly reactive and is used in small quantities to enhance the strength, durability, and impermeability
• Natural pozzolans, such as calcined clay, calcined shale, or volcanic ash, can be used as SCMs in cement manufacturing. They are rich in reactive silica and alumina and can improve concrete performance when properly processed and blended.
• Limestone and calcined clays (LC3) are materials that can be used in cement to reduce the clinker content. Limestone and clay are mixed with clinker, reducing the carbon dioxide emissions associated with traditional Portland cement.
“Use of alternative fuels and raw materials impacts the emission rates of the cement plant. 3 to 4 per cent of global greenhouse gas emissions are caused by landfills. Use of alternative fuels and raw materials avoids formation of dioxins and furans and
reduces Nox generation” says Amarjit Bhowmic, GM – Procurement (AFR Incharge), Heidelberg Cement India.
“CEMS is the quantity of hazardous substances coming from the stacks, measurements are performed every 2 seconds and are recorded in a secured place, where human access is not possible. Annual spot checks are done by a third party” he adds.
IMPACT OF SCMs
The use of SCMs in the production of cement can have several significant impacts, both positive and negative, on the cement manufacturing process. The most significant positive impact of using SCMs is the reduction in carbon emissions. SCMs allow for a partial replacement of clinker, which is the most energy-intensive and carbon-intensive component in cement production.
By using SCMs, cement manufacturers can reduce their greenhouse gas emissions, as clinker production is responsible for a substantial portion of the carbon footprint associated with cement. Additionally, the incorporation of SCMs typically requires less energy compared to clinker production, leading to cost savings and environmental benefits. This reduction in energy consumption also contributes to environmental sustainability by conserving natural resources.
Many SCMs can enhance the performance of cement, such as increasing durability, reducing heat of hydration, and improving workability. This can lead to better-quality concrete and greater customer satisfaction. Furthermore, SCMs are often derived from industrial byproducts or waste materials, and their use in cement production helps repurpose
and recycle these materials, reducing the need for landfill disposal.
Dr Hegde explains how by incorporating 20 per cent fly ash, a common SCM, into its cement mix, the plant can realise significant cost savings, in the following ways:
• Reduced raw material costs: Assuming a cost savings of Rs 200 per tonne (as fly ash is typically cheaper than clinker), the annual savings would be Rs 20 million.
• Energy savings: A 10 per cent reduction in energy costs due to reduced clinker production would result in savings of Rs 10 million.
• Transportation costs: Savings from reduced transportation costs might amount to Rs 5 million annually.
• Regulatory benefits: Tax incentives and compliance benefits might contribute another Rs 5 million.
This hypothetical case illustrates that by incorporating SCMs into their cement production processes, Indian cement manufacturers can potentially save Rs 40 million annually. These cost savings can significantly impact the overall profitability of the business. Beyond cost savings, this practice aligns with sustainability goals, reduces carbon emissions, and opens doors to regulatory benefits.
Kabra affirms, “With the use of this supplementary cementitious material, we are saving substantial heat value, electricity and natural minerals.”
As the Indian construction industry continues to expand, cement manufacturers should get the new amendment done as early as possible from BIS for higher addition of SCMs in blended cements and also get the new IS codes in place for ‘Newer and Emerging Cementitious’ materials in the months to come.
Role of Technology
Technology is fundamental to the effective use of supplementary cementitious materials in cement plants. It allows for precise control over material handling, quality, mix design, and production processes, resulting in more sustainable and high-performance cement products. Additionally, technology helps cement plants comply with environmental regulations and reduce their carbon footprint, contributing to a greener and more sustainable cement industry.
Advanced systems streamline SCMs handling and storage, employing automated conveyors and robotics to efficiently transport materials while minimising manual labour. Quality control is bolstered by cutting-edge technology, with online sensors and analytical instruments continuously monitoring SCMs properties to meet stringent standards.
Furthermore, advanced grinding and blending technologies ensure the homogeneous mixing of SCMs, enhancing reactivity in the final cement product. In the kiln, energy-efficient designs and alternative fuels are deployed to reduce energy consumption and carbon emissions during clinker production. Alternative clinker materials, activated SCMs, energy-efficient equipment, and emissions control technologies all contribute to a more sustainable and eco-friendly cement production process.
Cement manufacturing in India, like many parts of the world, faces the dual challenge of meeting the growing demand for construction materials while minimising its environmental impact. A critical strategy employed in this endeavour is the incorporation of SCMs in cement production.
As India continues to align its construction practices with global sustainability initiatives, these standards play a pivotal role in fostering innovation and responsible SCMs use in cement manufacturing. The collaboration between industry stakeholders and the BIS standards ensures that the nation’s construction materials are not only of high
quality but also environmentally conscious,contributing to a more sustainable and resilient built environment.
- –Kanika Mathur
Use of SCMs in Green Buildings
Arun Shukla, President and Director, JK Lakshmi Cement, elucidates how supplementary cementitious materials (SCMs) are evolving as an indispensable route toward a sustainable future.
Construction activities and large-scale infrastructure development form the bedrock of economic progress. At present, growing population, rapid urbanisation, commercialisation and increasing residential needs are catapulting demand for commercial, residential and industrial buildings. However, the alarming rise in environmental concerns including climate change and pollution have made it critical for the construction sector to prioritise sustainability for a greener and better future. As per reports, the construction sector accounts for 23 per cent of air pollution, 40 per cent of drinking water pollutants, and 50 per cent of landfill wastes. At this juncture, it thus becomes crucial to find the right balance between development and sustainability, and innovative concepts like green buildings have emerged as a practical solution for it.
While green buildings carry tremendous potential to reduce environmental impact, they further bring additional advantages such as improving energy efficiency, promoting better air quality and healthier ecosystems, efficient resource utilisation and minimising wastage. According to data, green buildings can reduce energy consumption by 20-30 per cent, water usage by 30-50 per cent, and significantly reduce waste generation through extensive recycling. Considering the rise in construction activities to meet the current and future demands, development of green building is both beneficial and a necessity.
Since utilising sustainable materials is key to promote green construction practices, the use of supplementary cementitious materials (SCMs) can take the benefits of green buildings to another level. SCMs are not only environmentally friendly, but are a potent solution to inch closer to sustainable development and decarbonisation goals as well.
Simply put, SCMs are materials or substances which are added to concrete to make it more environmentally friendly, durable and enhance its performance. They not only improve the strength of concrete but bring huge sustainability-related benefits as they require lower energy for production and support in reducing greenhouse gas emissions. As per estimates, for every tonne of clinker replaced by SCMs, the carbon dioxide emissions are reduced by around 0.8 tonnes.
It is noteworthy that SCMs are mostly by-products coming out from various industries, which makes them highly beneficial in terms of utilising waste materials and promoting efficient resource utilisation for both environmental and economic gains. The various types of SCMs that are used to enhance concrete’s performance and properties include fly ash which is a by-product of coal combustion in power plants. Fly ash contains silica and alumina and improves concrete workability, reducing heat generation and increasing long-term strength.
Another SCM is silica fume, which is a fine material produced during silicon metal and alloy production. It effectively strengthens concrete and reduces permeability. Moreover, natural pozzolans like volcanic ash, calcined clay are great options to enhance concrete workability, durability, and strength. Metakaolin, a calcined clay, is also beneficial in improving concrete’s properties and durability, particularly reducing permeability and increasing chemical resistance. Similarly, natural zeolites, minerals with a porous structure, enhance concrete workability and durability. These various kinds of SCMs in addition to offering diverse benefits, allow the construction industry to utilise by-products and waste materials and reduce the need for high energy-intensive cement manufacturing, promoting sustainability.
The demand for buildings is increasing rapidly and thus constructing green buildings is a solution to ensure this demand is met in an environmentally friendly manner. While green buildings definitely make it possible to create spaces which promote cleaner and healthier environments, the use of SCMs ensure their sustainability related advantages are multiplied, environmental impacts are reduced, resources are efficiently utilised, energy demand is lowered, and overall well-being is achieved.
For instance, use of SCMs in construction supports greenhouse gases reduction. The production of SCMs require less energy as compared to traditional cement and support in reducing carbon emission and use of fossil fuels to combat environmental challenges like depleting natural resources, climate change and air pollution.
The other advantage of using SCM is enhancing the durability of concrete. Mixing SCMs can make concrete long-lasting and efficient, promoting conservation of resources. By using durable concrete with SCMs during construction of green buildings, it becomes possible to reduce the need for frequent repairs, replacements, and extend the lifespan of buildings. For instance, materials such as fly ash and slag carry the potential to mitigate alkali-silica reactions which often lead to formation of cracks in buildings and impact concrete’s durability. By incorporating SCMs, it becomes possible to avoid the damaging effects and achieve stronger and structurally sound buildings with longer lifespans.
Most importantly, use of SCMs helps the construction industry to adopt responsible sourcing of materials, efficient utilisation of by-products and promote waste minimisation for sustainable development. Since most of these materials are by-products of various industries, integrating them
in construction not only supports efficient use of resources but further prevents them from ending up in landfills as waste, minimising their harmful environmental impact and potential health hazards to achieve healthier ecosystems for current and
In the current period where construction activities are growing constantly to satiate residential and commercial demands, green buildings developed using SCMs are a great way to promote sustainability. SCMs in green buildings are not only environmentally friendly but bring a host of advantages, which are essential to build a greener, healthier and better future for all.
Economic Implications of Using SCMs
ICR analyses how the integration of supplementary cementitious materials (SCM) and the strategies thereof has catalysed the cement industry’s economic landscape, fostering streamlined processes and enhanced resource utilisation, ultimately shaping a more resilient and profitable sector within India’s economy.
The way to look at any cementitious material in modern times would be to look at the carbon intensity inherent in it in terms of CO2 emissions, such as clinker, which forms the basis for making cement. After grinding the clinker (95 per cent) with gypsum and some correctives (together at 5 per cent), its emission intensity is 849-868 kg per tonne of output. Thus, when you produce ordinary Portland cement (OPC), which contains only clinker as the base cementitious material, the emission intensity is the highest at 750-860 kg of cement output. The lower end of the band is reserved for those who use the best technology that improves thermal efficiency and electrical efficiency.
Now, OPC could be the best suited for giving the early strength of cement measured by the compressive strength in MPa. Whether you take a 3-day or 7-day or 28-day strength, OPC would remain at the highest when you compare with any other form of cement that supplements clinker in the OPC with other cementitious materials like fly ash, slag, silica fume, natural pozzolans – such as calcined clays, shale and metakaolin, sugarcane bagass ash (SCBA) or rice husk ash (RHA).
The purpose of using supplementary cementitious material is two-fold:
The way to deal with this subject would be to look at the life cycle assessment of each of these and compute the impact. To make matters simple one may first look at the carbon intensity in each in terms of emissions and attach an appropriate environmental cost to it. Let us look at some of these numbers:
Portland Pozzolana Cement (PPC) uses a mix of 60-65 per cent clinker, 5 per cent gypsum and 25-30 per cent fly ash thus taking the overall emission to an average 700 kg per tonne of cement. Efforts have been always to look at ways of maximising fly ash and PPC specifications allow for even 35 per cent fly ash to meet the compressive strength guidelines. However, we must note that compressive strength will be lower for 3 days, 7 days and 28 days for PPC when compared with OPC by at least 8-10 per cent. If one considers the cost of fly ash that is replacing clinker, the economic impact is huge as the cost of the former is a fraction of the latter.
To compute the economic benefits of fly ash in PPC there are two important factors to be considered. The grinding units that are the final delivery points of cement units must be logistically located such that the cost of fly ash could be minimised. But this is a network optimisation question and the optimisation would entail outbound logistics cost of cement as well. Most advanced economies, India included, have looked at fly ash as an economic agent that not only turns waste into wealth but also reduces environmental impact of cement emissions (850 kg to 700 kg per tonne). The reduction in the landed cost of fly ash would further improve the economics through better logistics cost optimisation and mode-mix improvements. In recent times freight charges on rail in India for fly ash have been reduced to move fly ash over longer distances.
The environmental impact over long distance haulage of fly ash thus could be brought down
using rail as the mode, a crucial factor for the life cycle assessment.
The wider economic implication could be seen in the alternative deployment of a waste that was put to landfill is now an economic alternative to clinker. Some fly ash producers like NTPC or TATA Power or Adani Power, who together produce more than 100 million tonnes of fly ash per year, could be powerful actors to sway economic balance. Fly ash brick manufacturers who operate in the smaller concentrated networks, mostly SMEs, could be the next contenders in the value balance.
Slag based cement, uses 50 per cent clinker and 45 per cent slag and 5 per cent gypsum on an average. It is the next best example of SCM making a huge difference to the economic as well as environmental impact. By replacing a large amount of clinker, slag-based cement thus makes the emission intensity of cement come down to less than 500 kg per tonne of cement. This when looked at the back of the cost of slag vis-à-vis clinker, which it replaces in the cement, the economic implication is huge. The total production of blast furnace slag is growing, despite its environmental impact and it makes an economic case for GGBS.
However, blast furnace slag or the copper smelter slag, as inputs mixed together, is not free and must compete as commodities with clinker. But game theoretic approaches to price negotiations have fructified into either contracts that are short or medium term tenured (a sharp departure from the past) or pure spot contracts through auctions, that could be well mired in quasi-collusion dynamics of all kinds (in the past). Slag producers seeing an economic opportunity (as opposed to the environmental impact they face otherwise) have mostly experimented with a mix of spot and contracting strategy. The slag benefit in cement over clinker could be in the range of 30-40 per cent looking at the range of cost dynamics that would also include transportation cost by rail.
When one adds the CO2 emission impact benefit, fly ash and slag make a stunning case.
Exploring Other Options
The next most talked about SCMs are silica fumes and natural pozzolans, but their use has been limited in most parts of the world due to economic evaluations, including logistics cost. However, this economics could be lopsided in Europe where fly ash is hardly available and slag could be following suit. Natural pozzolans like calcined clay and metakaolin are therefore in news today, especially in Europe. In India, for example, they could be traded at cement cost, whereas in Europe they could well be lower than the clinker cost.
Utilisation of fly ash in cement has been improving in India but it is still far from the developed world numbers. The old wet fly ash lying in ponds and the dry lying in ash mounds could together be in excess of 100 million tonnes. While the vertical roller mills (VRM) technologies offer great benefits overall ball mills in grinding for absorption of wet fly ash, some innovative methods to use wet fly ash without adding to cost have been developed by some. Similarly, those having a logistics advantage towards a mix of fly ash and slag have settled for composite cement that could use a blend of fly ash and slag in their grinding mix. These could offer negotiating leverage while settling contracts in fly ash and slag.
At the end, to weigh the environmental impact in concrete, which uses a mix of sand, gravel, cement and water, one must see the equation differently: in a one cubic metre of concrete, using 14 per cent cement in the mix, the CO2 emission would be of the order of 410 kg/cubic metre compared to 290 kg per cubic using 30 per cent fly ash in PPC.
- –Procyon Mukherjee