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Efficient grinding unit selection impacts profitability



ICR gets Vimal Jain, Director – Technical, HeidelbergCement India, to share his views about the innovations in technology of the grinding process and grinding aids as well as his understanding on how the entire process can be made more energy-efficient and cost-effective.

Explain the grinding process in cement manufacturing.
The grinding process is needed to create surface area for a good chemical reaction and reactivity to occur in cement manufacturing. The grinding process is mainly required for raw material, coal and clinker grinding in the cement manufacturing process.
The process of cement manufacturing involves grinding clinker granules along with blending materials or additives and gypsum to produce a fine powder called cement. Depending on the quality of clinker and type of cement, blending material/gypsum are added in controlled proportion to produce a quality product to meet the prescribed quality as per given codes.
Optimum fineness needs to be found for the type of raw materials, coal, and clinker to avoid over-grinding, which comes with ‘excess energy’ consumption and has a negative impact on quality and cost.
The quality of cement depends on its physical and chemical properties. Technology has advanced over the period and the grinding process can help in augmenting some properties of cement.

Tell us about the equipment used for grinding raw material and clinker.
The main equipment used for grinding raw materials and clinker are categorised based on their size reduction concept and mechanism as,
Ball Mill (BM):
Size reduction mechanism –

  1. Impact: particle breakage by a single rigid force causing fracture.
  2. Attrition or Abrasion: arising from particles scraping against one another or against a
    rigid surface.
    Ball mills are the most widely installed grinding equipment in the cement industry. It consists of a rotating cylinder filled with steel balls that tumble inside the mill, applying impact and friction forces to the clinker particles. For better grinding efficiency, the mill may be operated with one, two or three internal compartments separated by diaphragms that prevent the transfer of the balls between the compartments while allowing the flow of the ground material through the mill.
    Roller Press (RP)
    Size reduction mechanism – Compression: particle disintegration by two rigid forces.
    The roller press has been extensively used as a pre-grinder as well as a stand-alone cement mill. It compresses the material in a gap between two counter-rotating grinding rollers lined with wear-resistant material. The output product contains fine and coarse particles with a large number of cracks and weak points that significantly reduce the energy requirement during the further stage of fine grinding.
    Vertical Roller Mill (VRM)
    Size reduction mechanism –
  3. Compression
  4. Shear or Chipping: produced by fluid or particle-particle interaction.
  5. Attrition or Abrasion
    In a vertical roller mill, two-four rollers turning on their axles press on a rotating grinding table mounted on the yoke of a gearbox. Pressure is exerted hydraulically. This mill also has a built-in high-efficiency separator above the rollers. The vertical roller mills offer high drying capacity, comparatively low energy consumption, and compactness.
    Hybrid Grinding: a combination of Ball Mill with Roller press
    Horo Mill (HM): it is similar to the vertical mill but the roller arrangement differs from VRM.
    In the ball mill, RP and Combined grinding system separation take place outside the grinding mill, whereas in the VRM separation and grinding take place in one system.
    The technologies involved in cement can be classified as per the following:
    Intergrinding: With the intergrinding process, all components of the blended cement are ground together. In that way, the cement is homogenised during the grinding, and at the cement plant only one silo is needed. Because of interactions between the different cement components due to differences in grindability, the PSD of the blended cement and the different components is difficult to control due to differential grindability due to different hardness of materials. Equipment for the inter grindings are Ball mills, roll press/ Pre-grinder + Ball mill, Horo mill, and VRMs.
    Separate grinding: The separate grinding process is grinding the various components separately, storing them, and mixing them according to the desired proportions. This process has several advantages: the PSD of each component and of the blended cement can be controlled according to the components’ hardness and required fineness, and appropriate grinding equipment can be used for each component. But in this case, several silos for storage are needed at the cement plant. Equipment for separate grinding is all the grinding equipment mentioned above, with the use of blenders required to blend the grounded material in the proportion needed for the specific cement product.
    The advantage of separate grinding can be to produce a wide range of cements from one plant.
    Grinding systems are either ‘open circuit’ or ‘closed circuit.’ In an open circuit system, the feed rate of the incoming clinker is adjusted to achieve the desired fineness of the product. In a closed circuit system, coarse particles are separated from the finer product and returned for further grinding.

What are the key functionalities that are looked at while installing a grinding unit in your plant?
The key factors, which shall be carefully considered, include:

  • Product quality requirement: market requirement
  • Machine sizing and layout: investment cost
  • Raw materials quality and characteristics: input materials
  • Mechanical design: maintenance cost and reliability
  • Latest design innovations including high grinding efficiency, energy saving and environmental protection, good quality of finished products, etc., performance improvement
  • On-demand changes: project-specific requirement
  • Product diversification: commercial reasons
  • Capex vs Opex economics: budget
  • Spare part and service availability: after-sales service

What is the contribution of grinding units in making cement-making processes efficient and productive?
The grinding unit plays an important role in making the operation efficient. Approximately 60 per cent of the cement power is absorbed in the grinding circuit, and to be competitive in the market, power cost plays an important role.
It is also observed that particle size distribution is better in the BM compared to other mills considering the product quality requirement.
The following grinding units are involved in cement making process:

  • Raw material grinding: to improve raw meal burning behavior, clinker quality, and kiln output, including thermal energy requirement
  • Coal grinding: better combustion of fuels, improves the flame property, and avoids CO2 generation, including improved burning process
  • Cement grinding: cement hydration, strength development, and water demand

How do grinding units contribute to the profitability of the cement-making process?
The grinding unit contributes to profitability in the following ways:
The electrical energy price is a major contributor to the cost of production. Therefore, producing cement with less energy is becoming a key element of profitability: as the grinding process consumes about 60 per cent of the total plant electrical energy demand and about 20 per cent of cement production variable cost. So efficient grinding unit selection impacts profitability of cement manufacturing. Optimum fineness needs to be found to avoid over grinding and consuming excess energy Final product PSD (particle size distribution) improves quality and profitability. Where two types of cement have identical surface areas, the cement with the narrower PSD will have a higher compressive strength.
Maximum use of low-cost blending materials, technology and layout such that the repairs and maintenance and manpower costs are lower, etc.

What are the materials and equipment that aid in the process of cement grinding?
Grinding Aid (GA):
In the grinding process, agglomeration takes place, due to this grinding efficiency is reduced and the output and quality of product effects. The GA is a very efficient way to avoid the agglomeration mechanism and improve the over-grinding efficiency. Therefore, GA helps to increase the grinding mill output and reduces
the electrical energy consumption, resulting in improving profitability.
Performance Enhancers/Quality Improvers: Due to the quality of raw materials and variation in the burning process, desired clinker phase formation does not take place, which impacts the cement performance, workability, and durability. Therefore, in addition to a grinding aid, additional chemicals are used to improve the cement performance and properties, such as setting time and strength development
Functional Additives: The additive imparts a specific property, such as air entrainment in masonry cement or chromium (VI) reduction.
Supplementary Cementitious Materials (SCM): Supplementary Cementitious Materials (SCMs) are added to cement mixtures for various reasons, including improving durability, decreasing permeability, aiding in pumpability, mitigating alkali reactivity, and improving the overall hardened properties of concrete. This also helps to reduce the carbon dioxide footprint in cement manufacturing. The use of SCMs also reduces the dependency on natural resources and enhances the circular economy.
Equipment: Raw materials storage, dosing station, raw material transport conveyors/elevators, weigh feeders, air separators, baghouse, product transport and storage silos are the key equipment of the grinding units.
Air Separator is one of the vital equipment for grinding systems that plays a significant role in maintaining product quality and increasing the grinding system productivity.
QC Lab: It’s a must for sampling and testing so that consistent quality material is produced and supplied to customers.

How do you ensure standards in the process?
During manufacturing, quality control parameters are established with reference to the national standards, and accordingly, the sampling and testing plan of the company is maintained.
There are very well descriptive quality control and assurance plans at various stages of the manufacturing/operations.
At each of our plants, we have state-of-the-art laboratories to produce quality cement much above the spec from the BIS. We have a very low standard deviation in the finished product that indicates the consistency in the cement. We are certified with applicable ISO standards to ensure that the product supplied is safe, environmentally compliant, and quality consistent.

How often is the same monitored?
Cement manufacturing is a continuous process and monitoring is done in 24×7 mode to ensure cement quality.
The quality control starts from the mine to the cement packing, and there are well-defined testing protocols at a sampling frequency. Plants are equipped with various material feeding and transportation systems to maintain the quality and process.

What challenges do you face in the process of cement grinding?
Availability and economics of outsourced materials are major challenges these days. The key challenges are as follows:

  • Availability of reliable and economical energy sources, power generation is becoming expensive due to increasing fuel prices and quality of fuel.
  • Right quality and Quantity of SCMs (Supplementary Cementitious Materials) are needed to achieve cement quality and also to mitigate the challenges of CO2 reduction in the cement-making process
  • Production of multiple cement types needs more storage facilities and impacts mill performance and product quality
  • SCMs with high moisture content demand drying arrangements resulting in a need for more capital as well as operational expenses.
  • Skilled manpower for operation and maintenance.

What are the innovations you would like to see in the technology of the grinding process and grinding aids?
Innovations play an important role in the cement industry. The quality of the product can be enhanced by adopting the right technology and the optimum key performance indicators for producing a quality product at a competitive price. We would like to see further innovation for:

  • Energy efficient equipment and drives to lower the power consumption
  • Separate grinding of cement to improve product quality and lower power consumption to reduce CO2 emission.
  • New hybrid formulations in grinding aid to improve product quality, specific energy consumption and reduce clinker ratio in cement.
  • Innovation for cement production by substituting max possible clinker incorporation by alternative / lower quality cementitious materials but maintaining the product quality.
  • New wear materials for enhancing the life of wear components to reduce the consumables cost per ton.

Kanika Mathur


Precast use of concrete promotes sustainability




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




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:

  • 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




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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