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The Future of Gypsum

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ICR charts out the evolution of gypsum and the role it plays in manufacturing in a bid to understand the economics of sustainability in cement production.

The word gypsum is derived from the Greek word ‘gypsos’ meaning ‘plaster.’ The quarries of the Montmartre district of Paris have long furnished burnt gypsum (calcined gypsum) used for various purposes, this dehydrated gypsum became known as plaster of Paris. The ability to harden or set when added with water makes it a very useful mineral for construction. In the mid-18th century, Gypsum was found to have great capabilities as a fertiliser. It is this connection as a fertiliser that today the world over phospho gypsum is now available aplenty as a by-product from fertiliser plants, and which can be gainfully used as an additive in the cement making process, replacing mineral gypsum.


The production of phosphate fertilisers requires breaking down calcium-containing phosphate rock with acid, producing calcium sulphate waste known as phospho-gypsum (PG). Similar is the case with the desulphurisation process of flue gas (to take out the SOx from the emissions) from power plants when natural limestone is used for this process resulting in FGD gypsum as the bi-product. This product is pure enough to replace natural gypsum in a wide variety of fields including drywalls, water treatment and cement set retarder.

Sustainability ahead
As a sustainability initiative, replacing natural gypsum scores better, but first let us understand the role of gypsum in the cement to concrete process.


The main purpose of adding gypsum in the cement is to slow down the hydration process of cement once it is mixed with water. The process involved in hydration of cement is that, when the water is added into cement, it starts reacting with the C3A (tricalcium aluminate, which is the main component of Portland cement) and hardens. The time taken in this process is very less, which doesn’t allow time for transporting, mixing and placing. When gypsum is added into the cement and water is added to it, reaction with C3A particles takes place to form ettringite. This ettringite is initially formed as very fine-grained crystals, which form a coating on the surface of the C3A particles. These crystals are too small to bridge the gaps between the particles of cement. The cement mix therefore remains plastic and workable. The time allowed for mixing, transporting and placing plays an important role in strength, composition and workability of concrete. As gypsum retards the process of hydration, it is termed as retarding agent of cement.


The role of gypsum in concrete making can be summarised as follows:

  1. Gypsum prevents flash setting of cement during manufacturing.
  2. It retards the setting time of cement.
  3. Allows a longer working time for mixing, transporting and placing.
  4. When water is mixed to cement aluminates and sulphates react and evolve some heat but gypsum acts as coolant and brings down the heat of hydration.
  5. Gypsum cements possess considerably greater strength and hardness as compared to non-gypsum cement.
  6. Water required in gypsum based cement for the hydration process is less.
    The use of gypsum as an additive in cement ranges from 2.5 to 5 per cent.
    In its natural form, gypsum can be found as thick layers in shale and as attractive crystals. No gypsum deposits are 100 per cent pure. It is usually found with deposits of a combination of the following: limestone, sand, shale, anhydrite and sometimes rock salt. To be a commercial deposit, gypsum content should be at least 75 per cent. But as mines get old the percentage of gypsum could be as low as 45 per cent in many of the natural deposits.

Logistically speaking
Gypsum mines or deposits can be found all over the world, but Spain, Thailand, United States, Turkey, Russia, UAE, Oman and Chile are the leading producers. India has deposits mainly in Rajasthan and that makes the logistics cost play an important role in the use of gypsum in cement and

in India. There are two components to be seen, the percentage of gypsum in the mineral (purity) that one is transporting and therefore total cost of moving it when compared with other forms of gypsum, which could be non-mineral, from synthetic or anhydrous to simply the spent acid or other forms of industrial or chemical waste.


The desulphurisation process itself now being made mandatory for all coal fired power plants creates an enormous opportunity for non-mineral gypsum to be used in cement. But the economics could be very tricky. Let us see the cost dynamics in some details as this could be the most sustainable way for producing gypsum for cement and concrete.


It is calculated that a 500 MW power plant would need 40,000T of limestone annually to take care of the SOx emissions through the desulphurisation process. This would amount to about 12 million tonne of limestone consumption (less than 3 per cent of the total limestone use per year) for the entire power generation of India. But the economics would lie in transportation. Even if limestone is available free of cost, the transportation cost including handling and royalty beyond 250 km could rise to Rs 1000/T as the landed cost at the power plant. The FGD gypsum after production would need to be transported to the cement grinding unit, which if more than 250 km would again cost the same. Thus the FGD gypsum would then compete with phospho gypsum, which is available aplenty in fertiliser or phosphate plants.


As these options compete with each other,use of natural gypsum would subside as the
enormous logistics cost of either importing it or transporting it across India would not be sustainable in the future.

Procyon Mukherjee

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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