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Grinding: Smarter Solutions

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Grinding might be an individual step in the cement production line but it is a crucial one, given the energy consumption and impact on the quality of output that it gives. ICR explores how grinding methods have evolved with the help of technology and with the use of modern-age grinding aids.

Grinding in the cement manufacturing process takes place at three stages: raw meal grinding, cement grinding, and raw coal grinding. The process mainly includes the mixed materials crushing, material batching, pre-grinding, fine grinding, powder classification, dust collecting, automatic control, and other technologies, making cement production high yield and high quality, in line with the requirements of energy-saving and emission reduction.
According to an article published in Journal of Materials Research and Technology, Volume 9, Issue 4, 2020, Grinding is a central process in mineral processing to achieve particle size reduction and mineral liberation, and is highly energy-intensive. It accounts for 50 per cent of power consumption in a concentrator. In general, grinding has poor energy efficiency and accounts for about 2 per cent to 3 per cent of the world’s generated electricity. Due to the depleting resources, the processing of refractory ores is becoming common. Such processes require fine grinding or ultrafine grinding to liberate the valuable minerals from gangue material; thus, energy-efficient technologies and strategies are required.


Post clinkerisation of raw material, the clinker is extracted from the tank and transported to the cement mill hopper by belt conveyors. A measured quantity of clinker and gypsum is fed into our closed-circuit ball mill which incorporates a high-efficiency separator. At this stage, the type of cement can be differentiated. For example, OPC is produced by the inter-grinding and blending of 95 per cent clinker with 5 per cent gypsum to a fineness of 280 sq m per kg. PPC is produced by the inter-grinding and blending of 65 per cent clinker with 30 per cent fly ash and 5 per cent gypsum to a fineness of 320 sq m per kg. Where, fineness is a controlled parameter for cement to ensure better hydration and strength development. Ground cement is then stored in a water-proof concrete silo for packing.
The cement grinding station is an individual step in the cement production line. The new-age cement grinding units adopt pre-grinding technology. It not only reduces the particles of feeding materials, but also helps to produce cracks and flaws inside the particles, which largely increase the production capacity of cement mill, reduce the energy consumption. Cement grinding station can greatly digest the slag, fly ash, slag, coal gangue and other industrial waste residues near the city, is a green industry.

Evolution of cement grinding technology
A cement mill is the equipment used to grind the hard, nodular clinker from the cement kiln into the fine grey powder that is cement. Historically, the hydraulic cements were known to be relatively soft and could be readily ground with the primitive technology of the day, using flat millstones. The emergence of Portland cement in the 1840s made grinding considerably more difficult, because the clinker produced by the kiln is often as hard as the millstone material. Because of this, cement continued to be ground very coarsely (typically 20 per cent over 100 μm particle diameter) until better grinding technology became available.
The year 1885 saw the development of specialised steel that led to the development of new forms of grinding equipment. With this the cement grinding became finer with time and advancement of technology and equipment. The progressive reduction in the proportion of larger, un-reactive cement particles has been partially responsible for the fourfold
increase in the strength of Portland cement during the twentieth century.
The principle of Grate Discharge grinding is nearly universally adapted in the cement grinding industry. Grate Discharge Ball Mills are the rule rather than the exception. Rod Mills for raw and finished grinding began to enter the picture. Larger and larger diameter mills have become common. Lengths tend to shorten.
Raw Cement Grinding: This phase may be a wet or dry grinding phase, the end product of it goes to the kiln. Typically, the materials ground includes limestone cement rock, marl or marine shells along with secondary materials like shale or clay. A typical raw mix consists of 75 per cent to 85 per cent limestone, 12 per cent to 25 per cent shale, and the balance materials in this mix consist of silica or quartzite and iron oxide. Exact proportioning of the same depends upon their chemical properties before and after calcining to cement clinker.
During the wet grinding of raw materials, a thorough mixing takes place during comminution, making the process more efficient and permitting a balanced feed direct to the grinding mill. Another pro of this process is the elimination of the dust hazard and cleaner plants. Theories suggest that where low cost fuel is available, the extra heat required during calcining, to drive off water in the process, is actually less costly than resorting to less efficient dry grinding. Improvements in air separators and more efficient dust collecting systems have minimised some of these problems to a point where present day costs become closely parallel.
Anirudh Dani, Grinding Unit Head, JK Cement Works, says, “Major key technical functionalities are production capacity, cement grade, special energy consumption, maintenance cost, construction cost etc., for the installation of the grinding unit. Further, major key strategic deciding factors are land availability, market demand, logistics optimisation, geographical analysis, raw material availability etc., for the finalisation of the cement grinding location.”


“Cement grinding cost is 40 to 45 per cent of variable cost of cement production. By effective control measures and minuscule innovations, we can achieve a significant impact on profit maximisation with environmental sustainability,” he adds.

Cement Grinding Machines
Equipment required for the cement grinding plant include cement roller press, cement silos, belt conveyors, cement mills, classifiers, bucket elevators, packing machines, etc. The grinding mill and cement roller press are the core equipment of the cement grinding units. These grinding mills directly decide the quality and cost of whole cement grinding unknit. There are three common solutions for cement grinding plants: cement roller press and ball mill, closed-circuit cement mill, and cement crusher and ball mill.
In the cement roller press and ball mill system, the ground materials from the roller press are first processed by the separator and divided into two parts: the coarse part and the fine part. The fine part is sent to the ball mill and ground to produce cement, the coarse part is returned to the roller press to be ground again. The finished product cement from this system also has wide particle size distribution and stable performance. With the invention of the V-type separator, the combined grinding system composed of roller press and ball mill has been developed to further reduce the energy consumption of the cement grinding process. This system is considered efficient and productive for the cement manufacturing process.
Cement grinding is a flexible and generally intermittent operation. With mills that have sufficient capacity to grind the clinker considerably faster than kilns produce, this allows them to meet the maximum demands when necessary: at other times, they can be run at a capacity less than full or they can be stopped completely.
Considering the consumption of energy, mills are known to have a capacity greater than that of clinker production, thus grinding can be done during periods that offer the most favourable energy rates. The power supply and charges vary from plant to plant and also the arrangements for programming the grinding.
Grinding can be either ‘open circuit’ or ‘closed circuit’. In an open-circuit system, the feed of incoming clinker is adjusted in such a way that it achieves the desired fineness of the product. In the present day, open circuits have become obsolete. However, in a closed-circuit system, coarse particles are separated from the finer product in a separator and then brought back to a mill for further grinding. Energy consumption, during grinding operation, whether raw material or finished products, is of paramount importance. Therefore, any innovation to reduce energy consumption is always watched closely not only in India but across the globe. Power generation, distribution and consumption are focused areas to many current world issues, controlling the industry’s energy usage is a matter of interest to different federal governments across the globe.

Grinding Aids for Cement
Cement grinding aids are added to the clinker during the grinding process for the prime reason of eliminating the coating effect of the clinker on grinding mill walls and to increase the production rate of cement keeping the surface area constant. They also allow cement to be transported in delivery trucks and storage in silos without lump formation. However, cement grinding aids also determine and improve the clinker grinding efficiency, power flowability, and strength development of binders. They also impact the mechanical properties of cement in a positive manner, such as, setting time, compressive strength, surface area, and mortar workability. The principal application of cement grinding aids concerns with the mill output and dry cement handling.
The demand for cement in the current day and age of urbanisation and industrialisation is growing steadily. Selection of cement for these purposes is mainly dependent on efficiency and low cost. Cement grinding aids are used to improve the efficiency of cement production and reduce energy consumption and current consumers of cement are making their choices of buying cement on these factors and grinding aids play a key role in determining the same.

Looking Ahead
According to a report by IMARC, the global cement grinding aid and performance enhancers market is expected to exhibit a CAGR of 3.68 per cent during 2022-2027.
Over the last few decades, in order to address the high energy consumption and scarcity of potable water for mineral processing, chemical additives or grinding aids have become a promising alternative in the cement manufacturing process. Also, studying the effect of grinding aids on size reduction units is crucial for the beneficiation value chain of minerals and the impact on downstream processes.
Grinding aids range from organic to inorganic chemicals. For example, organic chemicals include, polyols, alcohols, esters, amines, while, inorganic chemicals include, calcium oxide, sodium silicate, sodium carbonate, sodium chloride etc. The process of grinding cement is required to be efficient and productive. Grinding aids are added to support the same. Grinding efficiency is mainly evaluated based on energy consumed per given mass of material as a function of time. A study on these materials shows reduction in the energy consumption increases by increasing grinding aid dosage to a maximum, after which further addition gives no effect.
Vimal Jain, Director – Technical, Heidelberg Cement India Ltd., says, “Approximately 60 per cent of the consumed power of the whole process is absorbed in the grinding process. To be competitive in the market it is mandatory for any organisation to have a minimum power consumption. This would mean accordingly minimising our input cost.”
“Some of the older technology and older design of the mills used upto 45 units of energy per tonne of cement, but with the advancement of technology, the energy consumption is significantly reduced, thus reducing the cost for the same. This energy saving or reduction in use directly contributes to the profitability of the process,” he adds.
Energy conservation and reducing carbon emission are the primary motives of every cement making organisation. Grinding units are energy intensive sections of the manufacturing process, thus, need to be looked at with advanced technological support as well as material support with grinding aids. Continuous research and development is the solution to find newer materials that will help make the grinding process more productive and efficient, while simplifying the application and functionality for all those involved.

-Kanika Mathur

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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Concrete

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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Concrete

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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