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(Re)discovering Alternative Raw Materials are Essential to the Green Cement Plant

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As the realities of climate change continue to hit home, social pressure on heavy emitters is increasing and financial pressure will follow, forcing cement producers to act. The cement industry has a responsibility to follow through on its promises to decarbonise.

As a leading supplier to the industry, FLSmidth feels this responsibility keenly. This article is an overview of the options to decarbonise – reducing the clinker factor. As we will learn, the green cement plant of the future may not look so different from a plant you would see today, but it is. The difference is in the way it is operated, what is being put into it, and some of the supporting technology.

Fly ash – set to get a second wind
As the cement industry faces increasing scrutiny over its environmental footprint – no stone is left unturned in attempts to reduce CO2 emissions. Fly ash has been used for decades to avoid the resource intensive limestone clinker, but shortages have led experts to debate; have we reached the full potential for fly ash in cement or could harvesting landfills give fly ash a second wind?
Fly ash is a great supplementary cementitious material – it has the right properties, meaning that it reacts with lime to form cementitious compounds. It is a by-product from coal-firing industries, but in some cases has ended up in landfills – especially up until 1929, when it was first used in concrete to minimise the use of cement when building the massive Hoover Dam on the Colorado River in the USA.
With the potential to replace up to 30 per cent of traditional clinker, fly ash quickly became very attractive to the cement industry and a sought-after commodity. Today, as the green transition of power plants and other heavy industry is accelerating – some countries are phasing out coal and turning towards green energy, natural gas, and/or biofuels, with the result being that fly ash is now in short supply.But just as steel, paper and sugar industries are eager to minimise their environmental footprint, so is cement. And the use of fly ash is both a proven and effective ingredient. The shortage of fresh fly ash has led more and more industry stakeholders to turn their attention towards the centuries of landfilled fly ash.
To date, billions of tonnes of fly ash have been landfilled. ‘Harvesting’ fly ash from these landfills makes some industry experts confident that this waste-product could have a second wind in cement.
“As we strive towards fulfilling our MissionZero promise of enabling net zero cement production by 2030, we need every tool in the toolbox. Reducing the clinker factor is a key element to that. Fly ash is a proven and well-integrated SCM – to pursue the exploitation of landfilled fly ash would obviously boost our efforts.”
To Thomas Petithuguenin, Head of Research and Partnerships for Cement, FLSmidth, every possible path to MissionZero needs to be explored.
“I am not saying that fly ash harvesting is a quick-win, but from a product point of view, it is a known ingredient and gives confidence in terms of quality and performance. The challenge is the logistics and infrastructure, which we need to investigate with stakeholders across the value chain.”

Upcycled concrete – a massive business opportunity
Repurposing of construction waste is a global, multi-billion-dollar business – to the cement industry it looks to be a win-win situation. As the world’s leading equipment supplier to both the Cement- and Mining industries, FLSmidth is well-positioned to support its customers in capturing a piece of the pie, says Petithuguenin.
At an annual growth rate of 4 per cent, the global construction and demolition waste management market is projected to be worth $142.92 billion in 2028. Combined with the cement industry’s acute need to reduce its environmental footprint, we see an increasing interest from customers exploring how to enter the market.
The recycling of concrete is not a new business case – different technologies and applications have been deployed for decades, but most often in terms of ‘downcycling’ where material will end up as road fill. Today, the average Construction and Demolition Waste (CDW) recycling rate in Europe is around 70 per cent and even though it still substitutes the use of virgin material, actual ‘upcycling’ has a massive potential of producing high-value materials out of tonnes of construction waste every year.
By upcycling concrete, we are not only able to leave virgin, raw materials in the ground, we are also able to reduce the need for traditional, resource-intensive clinker. At a time when no stone is left unturned in the quest for CO2 savings from cement production, reusing recycled cement fines as a filler, supplementary cementitious material (SCM) or by converting them into belite clinker is an attractive business-case.
The sustainability aspects of upcycling go hand-in-hand with cost-savings from eliminating the excavation of new raw-materials and a majority of the fuel and energy required for the calcination process of limestone.
According to the International Energy Association, the integration of emerging technologies like lowering the clinker-factor in cement and carbon capture is identified to provide some of the largest cumulative CO2 reductions in the 2-degree Celsius Scenario (2DS) compared to the Reference Technology Scenario (RTS) by 2050.
As we move into an industrial scale process of turning old concrete to a new cementitious material, we would need to do a few extra steps to get as pure aggregates, sand and cement fines as possible. A procedure that involves process knowledge within crushing and screening and just as important, some heavy-duty equipment such as a jaw crusher, impact crusher, cone crusher, elliptical screens, classifiers, and bag filters.
After crushing, the aggregates and sand are used in new concrete, with the potential to substitute 100% of the natural aggregates and sand needed. The cement fines, left from the crushing and grinding are ready to be converted into a belite clinker, most likely at an urban processing plant, whereafter it is mixed with OPC clinker at a 30-70 per cent ratio and reused on site – reducing the climate footprint of both the old and new building, bridge or road project. Another option is to take the cement fines back into the cement industry and carbonate them, which will activate them to SCMs – allowing their mixing with clinker (and reducing the clicker proportion, therefore, the CO2 emissions).
Today, an office building has an expected lifespan of 20 years, and a residential building a lifespan of 30-50 years. That’s extremely short and underlines the need for upcycling. If the industry is to support an accelerating urbanisation, the winners of the construction industry will be the ones who see opportunities in waste, which can be used again and again. And they will be the ones getting the building-licences from government authorities.

Mine tailings – a potential goldmine for cement
Tailings are both a safety issue and a huge financial burden to miners. But to cement and concrete producers they might hold a massive reservoir of untapped potential. With a shared ambition to reduce the environmental footprint of both cement and mining operations, FLSmidth is well-positioned to support its customers inturning mine tailings into value-added products, says Petithuguenin.
Mine tailings are the leftovers after the processing and extraction of metals and minerals from the basic ores. The total amount of mine tailings in active and inactive, closed storages around the world is estimated at more than 200 km3. Any attempt to describe the volumes easily fails as these enormous amounts are hard to grasp, but imagine a cube, six by six kilometres, weighing approximately 280 billion tonnes.
As an old proverb goes, ‘one man’s trash is another man’s treasure’. To miners, mine tailings are a costly by-product, which are difficult to manage due to the large quantities. They can pose a safety risk due to the instability of storage facilities further hampered by the material fineness and moisture content. Some of these challenges are mitigated with tailings storage solutions such as dry-stacking, backfilling the tailings material in old mine pits, and using them as aggregates in the construction industry. However, for many miners, safe and secure tailings storage is still a major issue.
To others, the mine tailings present an opportunity as an alternative building material or potentially even a carbon sink if there is a CO2 source nearby. Recent research shows that mine tailings can be processed to form supplementary cementitious materials (SCM) or geopolymers.
The mining industry recognises the prospect of turning mine tailings into value-added products, while also focusing on reducing tailings altogether.
“Increasing demand for metals critical to the energy transition, such as copper and nickel, will lead to greater production of mine waste like tailings under the current production processes. Alongside our members’ commitment to the safe management of their tailings facilities, ICMM’s goal is to significantly reduce or eliminate tailings. As part of this, we are working with members to make operations at their mine sites more circular by improving process efficiencies to reduce waste at its source, as well as creating value from waste such as tailings,” says Christian Spano, Director of Innovation, International Council on Mining and Metals (ICMM).
Reducing the use of the resource-intensive clinker in cement production is one of the technologies that will provide the largest cumulative CO2 reductions in the 2-degree Celsius Scenario (2DS), according to the International Energy Association. And with the urgency of climate change – no stone should be left unturned by the cement industry in its quest for CO2 saving – reusing mine tailings as a filler or an SCM can be an attractive business-case.
“As a leading supplier to both the cement and mining industry, FLSmidth is in a unique position to engage both parties to establish an efficient and commercially viable value chain for both industries,” says Petithuguenin – working closely with colleagues on both sides of the aisle to connect the dots. “The idea of using mine tailings in construction is not new, but the increasing need for sustainable SCMs is accelerating efforts to establish large-scale processes. In this work, which will include universities and experts from across different sectors, FLSmidth will use its vast process knowledge to optimise designs of the technology needed to produce a quality output.”

Concrete

Precast use of concrete promotes sustainability

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Vijay Shah, Managing Partner, India Precast, advocates the use of precast concrete as he puts forth details about its manufacturing, uses and methods while emphasising the sustainability of the product.

Explain the process of casting concrete in shapes and what is the grade of concrete used for making these shapes?
Precast casting concrete elements are manufactured with the required steel reinforcement either in formwork, moulds or on steel plates with side shuttering etc. The concrete cast is made at a different location and is then transported to the site. Precast elements are made of minimum M20 to M50 grade of concrete.

What is the difference between precast and cast in-situ as uses of concrete?

  • The use of concrete in the precast method and the cast in-situ method differs widely based on many factors.
  • Precast concrete shapes are cast at a different location and are then transported to the site where construction work takes place while with the cast in-situ process, concrete is poured on-site.
  • Curing of precast concrete is fast as it takes place under ideal and controlled conditions while the cast in-situ concrete takes relatively longer to get cured but can be easily used for two-way structural systems.
  • For the precast concrete, the process is easy to do and is repeatable as the same moulds or framework can be used. This increases the value of construction and derives more value
  • while cast in-situ adapts building shapes and post tensioning.
  • The work and rework in the usage of precast shapes is less, thus, reduces cost at the site
  • while with the cast in-situ method there is a requirement of space allotment for concrete mix and necessary add-ins, that is added cost for the construction job.

Tell us about prestressed and reinforced concrete.
Prestressed concrete is a combination of high strength concrete and tensioned steel strands. This combination makes a strong structural unit that is useful in building roof slabs, bridge girders etc. Reinforced concrete is manufactured from a combination of high strength concrete and normal reinforcement bars.

Tell us more about the precast elements manufactured, their shapes and sizes.
Precast is one of the best ways to rapidly build industrial buildings, commercial buildings, affordable housing, mass, EWS, LIG housing, schools, hospitals, public buildings, agriculture railways, stadiums, sport centres, parking, bridges, airports etc. They have a higher productivity and quality set at industry level.
Various types of precast elements manufactures are:

  • Solid load bearing floor slabs, load bearing walls, facades, sandwich wall panels and cladding panels
  • Floor and roof slabs are made from prestressed load bearing hollow core concrete slab and ribbed slabs. They are also made from half floor slab or semi-finished floor slab with a lattice girder
  • Precast stair cases, balcony, toilet pods, lift shafts, water tanks
  • Prestressed lintel, frames, beams, columns and double-tee beams
  • Internal partition walls are made with light-weight hollow core wall panels instead of AAC blocks or bricks
  • Boundary walls, fencing poles, U-drainage or trenches, box culvert etc.

What is hollowcore concrete flooring and what is its lifespan?
Hollowcore slabs are precast, prestressed concrete elements that are generally used for flooring. Some of the advantages of using these flooring are longer lifespans and no propping, flexibility in designs, faster construction, lightweight structures, fire resistant structures, high load capacities and units manufactured specific to the project.
The maximum span of hollowcore floors will depend on the floor depth and the specific loadings imposed on the floor.

What are the quality standards followed while making precast shapes for any project?
Quality control is a very important aspect in the process of making precast concrete shapes. It is imperative to make precast shapes as per the exact requirement provided by the engineers and the construction party. To maintain the quality of product from our end,

  • We ensure there are quality control systems and procedures in place along with a quality assurance plan. Our programme consists of tests, trials, and general procedures for acceptance.
  • There is a laboratory and related facilities, which are required for the selection and control of the quality of materials and workmanship. The central quality laboratory is used for various quality control tests like cube test, workability test, slump test, sieve analysis etc. The materials used for making the final precast shapes also has to be shared for testing to various third-party laboratories with an advance intimation.
  • All the necessary tests are carried out in respective batching plants or sites depending on the use of concrete at our facility.
  • Documentation for all the tests conducted and their reports is maintained in records, for references and submission to the relevant authorities and the users of the same.

As precast use of concrete is conducted in a dedicated space and is in a monitored environment, it becomes easier to maintain high quality due to its repeatability factor. The necessary general precast machinery and moulds, steel tables, concrete batching and dispensing equipment, vibrating and finishing equipment and dedicated labour team help maintain the higher quality standards as compared to cast in-situ use of concrete.

How do you incorporate sustainability in the process of precasting?
Precast use of concrete promotes sustainability with its repeatability factor. There’s more planning involved in the process and equipment like the moulds, vibrating machine, finishing machine are all reusable elements of the process.
As mentioned, there is planning in precast use of concrete where only the required measure of concrete is mixed and poured into moulds that are made to precision as per the requirement of the project. The quantity is also previously defined, which means there is reduced to zero wastage of material.
This waste reduction leads to lesser needs of cleaning and clearing equipment, which may further be fueled by other energy sources. Thus, precast concrete, by large, is a sustainable means of building.

What are the advantages of using precast concrete?
There are multiple advantages of using a precast structure for any project like cost efficiency, speed, versatility, safety, sustainability and beauty.
This includes:

  • The use of precast improves the quality and lifespan of any building
  • It reduces the time of building, thus reducing the costs involved for all the other equipment and labour that goes in to the project, thus, proving to be cost effective
  • The maintenance of a precast is lower due to its high quality and durability that is ensured while it is cast
  • This method of using concrete is a sustainable option due to its repeatability

What are the major challenges you face in the process of making precast shapes and in their transportation?
The precast industry plays on volume and repetition. This is one of the major challenges as well.
The requirement of having to repeat the process
that contains a large volume of mixed concrete and getting the same perfection in the shapes is a cumbersome process.
The initial investment in setting up the precast plant and acquiring all equipment and moulds is high. With bulk shapes to be transported from one place to another and the requirement for site space and handling, this time of concrete use is more suitable for tier 2 and tier 3 cities.

How do precast elements or shapes help in the profitability of a construction activity?
As precast concrete is made at a different location than the construction site, the other jobs keep going on at the site and then the precast shapes are placed there. This reduces construction time to up to one-third to one-fifth as compared to cast in-situ concrete, thus, reducing cost of the construction.
Construction maintenance is reduced as the quality of their precast structures are monitored and carefully administered at the plant level. This means it adds to the reliability, durability, accuracy, and ability to produce architectural elements in any building adding to its quality and strength. Precast also provides insulation, thermal inertia and fire resistance and the possibility of integration with MEP (Mechanical, Electrical and Plumbing) from the start of the project.

How can precast concrete contribute towards affordable mass housing in India?
Defined shapes and technical requirements in precast concrete helps reduce the waste and increase the repeatability factor, thus, reduces the cost and time for any construction or building project. Higher control on quality, less time consumer leads to lesser need of labour and equipment on-site, which also adds to the profitability of the structure.
All factors combined bring down the overall cost of the project, leading to that benefit translating to the end consumer and bringing a surge of affordable mass housing in India.

-Kanika Mathur

Comparison Between Cast-in-situ (conventional method) versus Technology Drive Precast

Sr. No Criteria Conventional Construction Precast Construction 3D Modular/ Panel & Hollow Core Slab.
1 Natural resource consumption High 30 per cent saving
2 Labour Problem Heavy labour problem while work in progress Less labour required
3 Dependability on skilled labor 60 per cent Dependability
4 Time consuming Verv High Fast track
5 Initial investment Low High
6 Finishin Normal Excellent
7 Quality production Poor Excellent as factory based.
8 Material wastage High Least
9 Speed/ Productivity Low Excellent
10 Strength Good Excellent
11 Durability Low High
12 Structure weight/ Deed load Very heavy Reduced
13 Brick Block and Plastering Required No Need
14 Service like Electrical, plumbing & sanitary Break, Provide & Re-build Pre-embedded

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The age of concrete blocks can be up to a 100 years

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Nikita George, Director Operations, APCO Concrete Blocks and Allied Products, takes us through the manufacturing process of concrete blocks and its composition and also specifically discusses their patented product – cellular blocks.

Tell us about the type of concrete blocks that your organisation manufactures.
We manufacture mainly solid and cellular concrete blocks. The cellular block is our patented product, which has become increasingly popular due to its high utility value in the construction process. We are also gearing up to launch our new line of pavers and kerb stones by the end of August.

What is the composition of each type of block and what are their strengths?
Blocks constitute of mainly three items:
Cement,

  • Manufactured Sand and Stone Aggregates Our patented cellular blocks have a vast set of benefits:
  • Lightweight: The cellular block is between 8 to 9 kg lighter than the solid block. This not only increases the productivity of the labour but also helps in reducing the overall steel requirement for the project.
  • Thermal insulation properties: With the erratic weather conditions in India today, cellular blocks help in maintaining thermal insulation properties within the building. In a recent experiment conducted on a building, which used the cellular blocks, a marked reduction in temperature by three degrees was recorded.
  • Sound insulation properties: Due to the hollow nature of these concrete blocks, the product is able to cut the decibel levels by 14 per cent.
  • Compressive strength and water absorption properties: The cellular blocks exceed the ISO parameters for compressive strength and water absorption.

How do you ensure quality standards for the concrete blocks manufactured?
With our 50 years of experience in the concrete blocks manufacturing industry, we have continually evolved and tried our best to stay relevant with the international quality standards. Quality control begins with procurement of good quality raw material. Fortunately, we have our own crushers to cater to our production units. This helps us negate undesirable raw materials. State of the art machinery and a strong base of SOP help mitigate errors. Above all, of these we have a skilled set of managers who have over 25 years of experience in the concrete blocks field.

Tell us about the sustainability and environmental benefit while manufacturing and while using these blocks in construction?
The blocks that we manufacture follow the highest quality parameters that give a very long life span. When used in building, the age of concrete blocks can be up to 100 years. The blocks used in these buildings at the time of demolition can be re-crushed and used to manufacture the same product again. And since concrete blocks are one of the strongest products available in the market, the on site damages are virtually zero. Unlike native methods of concrete production, we use only M-sand. There is no usage of river sand hence, safeguarding our environment. Also, as mentioned before, concrete blocks can be reused even after the lifespan of a building. This cuts down on further usage of raw materials.

What are the key benefits that any builder can get from using your concrete blocks?
The concrete blocks industry to a large extent can still be categorised in the unorganised sector. Due to this, there is a lot of disparity in pricing and quality in the market. At APCO, with our 50 years of experience, we have won the trust of our customers by consistently proving the highest quality of our products and on-time delivery.
With our 5 production units strategically located around Bangalore city, we have the capability of producing up to one lakh blocks per day. This allows us to consistently supply large quantities to our customers. Our customers can also be assured that the quantity of blocks that leave our plants is the same quantity that will be unloaded at the site.
Apart from this as mentioned in the earlier answers, our cellular blocks host a wide range of benefits during and even after the construction of a building.

How do these concrete blocks contribute to the profitability of construction?
When APCO came into the market in the early ’70s, the construction industry was heavily reliant on the traditional clay bricks. It took us about 10 years before we got our first big break. And since then, the construction market has not looked back. There have been multiple competitors in the walling solutions market but in terms of pricing and quality no other product comes close. Most people build a house once. At APCO, we believe in making that house a home. We provide unrivalled quality and a fair price to all our customers!

What does the near future hold for APCO Concrete Blocks and allied products?
We will be launching our new product line of pavers and kerb stones by August and we are working towards APCO being present in a few more states around India.

Kanika Mathur

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Effects of Macronomics

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In any industry, it always helps to take into account the macro perspective as it aids one in navigating the broader economic trends. As per the assessments of the April-June quarter (Q1), India’s gross domestic product (GDP) increased 13.5 per cent, which was lower than RBI’s estimated 16.2 per cent. A fiscal deficit of Rs 3.41 trillion was noted during the April-July period this financial year.


Moody’s Investors Service has revised India’s economic growth projection for 2022 to a reduced 7.7 per cent. The downward revision is due to rising interest rates, an uneven monsoon and global demand slowdown, which is not surprising as the Russia-Ukraine war continues to cast its shadow. The eight core infrastructure sectors, including cement, slowed down to 4.5 per cent in July, which afforded the service sector to shine in the first quarter.


Taking a bird’s eye view of the cement sector, the upward moving trends are looking promising and that has kept optimism buoyed amongst the players. Monsoon is a tricky time for the cement industry as construction takes a backseat and price fluctuations in cement are rife.

As per Kotak Institutional Equities report, cement prices have declined about a percent sequentially in the second quarter. Cement price was recorded at Rs 384 per 50 kg bag in August pan-India. In spite of a sluggish season, the demand is likely to soar in the coming months, and the key players in the industry are anticipating robust growth.


There is a lot that’s underway for cement manufacturers in terms of alternative raw materials, energy efficiency and eco-friendly processes. Given the infrastructure and construction boom that India is witnessing today, the cement segment is likely to perform well. However, the challenges that the sector faces are unique to it, and it remains to be seen how cement brands will innovate to overcome them.

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