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Using Slag as Fine Aggregate in Concrete

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Disposal of waste slag is a major concern and is perceived as an environmental hazard across the steel industry. Nagesh Veeturi, Executive Director – Civil, and Sumanta Sahu, DGM – Quality, KEC International, investigate the possibility of utilising slag as a fine aggregate and its effect on the strength and workability parameters of concrete.

Concrete is one of the major construction materials in civil construction. It is a composite material with cement, aggregate, sand, admixture and water as ingredients. River sand and Manufactured Sand are mostly used as fine aggregate in concrete. River sand is formed by the natural weathering of rocks over many years and is preferred to be used as fine aggregate. Manufactured Sand is produced by crushing hard rocks into smaller sizes using a crusher followed by washing to use in concrete. The growth of infrastructure and building projects demand the use of huge quantities of sand in concrete.
The mining of sand from riverbeds is posing a serious threat to the environment causing the erosion of riverbeds and banks, triggering landslides, inducing loss of vegetation on the riverbanks, lowering the underground water table, etc. Hence, sand mining from riverbeds and rock is being restricted or banned by the authorities nowadays. To nullify the above concerns, concrete mix trials were conducted in our quality laboratory by using LD slag and blast furnace slag as fine aggregate.

LD Slag
LD slag is a byproduct of the steel industry. It is produced from impurities during the steel-making process. LD Slag consists of calcium, magnesium, iron, silicon and aluminium oxides minerals. During the production of steel, the slag is separated from steel in the furnace, and steel slag fine aggregate is formed after quenching the molten slag with water. There are many grades of steel produced and properties of steel slag vary depending on raw materials used for steel production. LD slag is typically granulated and used as a fine aggregate. Normally it is heavier than sand and its specific gravity is observed to be 3.2 to 3.6 with water absorption around 3 per cent.

Production process of LD Slag.
Due to its high density, segregation is observed as a fine aggregate in concrete. Materials can be used as partial replacement of fine aggregate.

Blast furnace slag
Blast furnace slag is a byproduct produced during the iron making process in blast furnaces. During the smelting process, iron ores are fed into the furnace at high temperature. The process leads to the production of molten iron and waste materials. Slag, which is a waste material, is separated and quenched with water. This rapid cooling process solidifies the slag into granular particles. Blast furnace slag is observed to be lighter than sand, specific gravity of sand is found to be 2.01.

Concrete mixes with slag as fine aggregate
Concrete mix trials were conducted with LD slag, BF slag as fine aggregate. Due to the high density of LD slag, segregation was noticed on concrete mixes. The same segregation is observed in concrete mix by using BF slag due to its lightweight. Further concrete mix trials were conducted by mixing LD slag and BF slag with different proportions – this is done to study the initial properties of concrete such as cohesiveness and workability retention.
The concrete mix is observed to be cohesive
with good workability retention by using LD slag and BF slag as fine aggregate with the same
proportions. Other properties of concrete such as setting, and strength were observed complying to specification requirements.

Benefits of using LD slag and BF slag as fine aggregate
Durability:
Calcium oxide and silicon oxide are prime chemicals used in the composition of LD slag and BF slag, and both possess pozzolanic properties. calcium oxide and silicon oxide react with calcium hydroxide produced during hydration of cement and increases strength and permeability properties
of concrete.
Sustainable approach: LD slag and BF slag are the by-products from the iron industry which makes it an industrial waste product. Using materials as fine aggregate helps to conserve natural resources. Storage of this material is a major concern in industry. Utilisation of LD slag and BF slag as fine aggregate minimise storage area, air pollution.
Reduction in carbon footprint and heat of hydration: The use of LD slag and BF slag as a fine aggregate leads to reduction in cement content in concrete mixes. Cement is a major source of rise in temperature in concrete mixes that leads to increase in carbon emission during its production process. Reduction in cement content minimises the heat of hydration and prevents thermal cracks in concrete.
Enhance workability in concrete mixes: Workability in concrete is increased due to the even surface of LD slag and BF slag. This makes the concrete easier to place during the construction process.
Cost optimisation: LD slag and BF slag are industrial waste products and are cheaper than manufactured sand and river sand. Also due to the pozzolanic properties of slag, cement content in concrete can be minimised. Overall concrete cost is reduced with improved performance.
Due to the vast growth of construction sectors, the demand for concrete has increased as a fine aggregate. Thus, it is essential to find suitable alternatives to sand such as slag materials.
It is observed that the combined use of LD slag and BF slag as fine aggregates leads to cohesive mix with desired workability and strength. The PC base chemical admixture was added to reduce the water content and maintain workability of the mix. Finally, it is concluded that slag can be used as an alternative of sand in concrete. As both types of slags are by-products from the steel industry, their long-term performance is vital, and further studies in this direction are still in progress.

ABOUT THE AUTHOR:
Nagesh Veeturi, Executive Director – Civil, KEC International
is a seasoned professional having entrepreneurial and leadership skills with key focus on strategy and business transformation.

Sumata Sahu, DGM – Quality, KEC International has 32 years of rich experience in the construction industry mainly as QA/QC and project management professional.

Concrete

Organisations valuing gender diversity achieve higher profitability

Aparna Reddy, Executive Director, Aparna Enterprises talks about company plans.

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The building materials industry is projected to grow by 8-12 per cent over the next five years. How is Aparna Enterprises positioning itself to leverage this momentum and solidify its market presence?
The Indian construction and building materials industry is projected to witness significant expansion, with estimates suggesting an 8-12 per cent compound annual growth rate (CAGR) over the next five years. This growth is fuelled by rapid urbanisation, increased infrastructure investments and sustainability-focused policies. With India’s real-estate market expected to reach $ 1 trillion by 2030, the demand for high-quality building materials is at an all-time high.
The Government of India’s flagship programmes, such as PM Gati Shakti, the Smart Cities Mission and the Housing for All (PMAY-Urban) initiative, are key drivers of this surge. The infrastructure sector alone is expected to receive a budgetary push of over Rs 11 trillion in FY25, with enhanced capital expenditure allocation.
At Aparna Enterprises, we are proactively aligning with this momentum through capacity expansion, product diversification, and cutting-edge technological integration. 

Our key strategic priorities include:
  • Expanding operations in high-growth regions across Tier-2 and Tier-3 cities, ensuring access to quality building materials nationwide
  • Investing in automation, AI-driven quality control systems and digital integration, enhancing efficiency and precision in manufacturing
  • Scaling up production capabilities in our RMC, tiles, uPVC and other divisions to meet the anticipated surge in demand.

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Concrete

Global Start-Up Challenge Launched to Drive Net Zero Concrete Solutions

Innovandi Open Challenge aims to connect start-ups with GCCA members to develop innovations

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Start-ups worldwide are invited to contribute to the global cement and concrete industry’s efforts to reduce CO2 emissions and combat climate change. The Global Cement and Concrete Association (GCCA) and its members are calling for applicants for the Innovandi Open Challenge 2025.

Now in its fourth year, the Innovandi Open Challenge aims to connect start-ups with GCCA members to develop innovations that help decarbonise the cement and concrete industry.

The challenge is seeking start-ups working on next-generation materials for net-zero concrete, such as low-carbon admixtures, supplementary cementitious materials (SCMs), activators, or binders. Innovations in these areas could help reduce the carbon-intensive element of cement, clinker, and integrate cutting-edge materials to lower CO2 emissions.

Thomas Guillot, GCCA’s Chief Executive, stated, “Advanced production methods are already decarbonising cement and concrete worldwide. Through the Innovandi Open Challenge, we aim to accelerate our industry’s progress towards net-zero concrete.”

Concrete is the second most widely used material on Earth, and its decarbonisation is critical to achieving net-zero emissions across the global construction sector.

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Concrete

StarBigBloc Acquires Land for AAC Blocks Greenfield Facility in Indore

The company introduced NXTGRIP Tile Adhesives alongside its trusted NXTFIX and NXTPLAST brands.

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StarBigBloc Building Material, a wholly-owned subsidiary of BigBloc Construction, one of the largest manufacturers of Aerated Autoclaved Concrete (AAC) Blocks, Bricks and ALC Panels in India has acquired land for setting up a green field facility for AAC Blocks in Indore, Madhya Pradesh. Company has purchased approx. 57,500 sq. mts. land at Khasra No. 382, 387, 389/2, Gram Nimrani, Tehsil Kasrawad, District – Khargone, Madhya Pradesh for the purpose of AAC Blocks business expansion in central India. The total consideration for the land deal is Rs 60 million and Stamp duty.

StarBigBloc Building Material Ltd currently operates one plant at Kheda near Ahmedabad with an installed capacity of 250,000 cubic meters per annum, serving most part of Gujarat, upto Udaipur in Rajasthan, and till Indore in Madhya Pradesh. The capacity utilisation at Starbigbloc Building Material Ltd for the third quarter was 75 per cent. The planned expansion will enable the company to establish a stronger presence in Madhya Pradesh and surrounding regions. Reaffirming its commitment to the Green Initiative, it has also installed a 800 KW solar rooftop power project — a significant step toward sustainability and lowering its carbon footprint.

Narayan Saboo, Chairman, Bigbloc Construction said “The AAC block industry is set to play a pivotal role in India’s construction sector, and our company is ready for a significant leap forward. The proposed expansion in Indore, Madhya Pradesh aligns with our growth strategy, focusing on geographic expansion, R&D investments, product diversification, and strategic branding and marketing initiatives to enhance visibility, increase market share, and strengthen stakeholder trust.”

Bigbloc Construction has recently expanded into construction chemicals with Block Jointing Mortar, Ready Mix Plaster, and Tile Adhesives, tapping into high-demand segments. The company introduced NXTGRIP Tile Adhesives alongside its trusted NXTFIX and NXTPLAST brands, ensuring superior bonding, strength, and performance.

In May 2024, the board of directors approved fund-raising through SME IPO or Preferential issue to support expansion plans of Starbigboc Building Material subject to requisite approvals and market conditions, Starbigboc Building Material aims to expand its production capacity from current 250,000 cubic meters per annum to over 1.2 million cubic meters per annum in the next 4-5 years. Company is targeting revenues of Rs 4.28 billion by FY27-28, with an expected EBITDA of Rs 1.25 billion and net profit of Rs 800 million. In FY23-24, the company reported revenues of Rs 940.18 million, achieving a revenue CAGR of over 21 per cent in the last four years.

Incorporated in 2015, BigBloc Construction is one of the largest and only listed AAC block manufacturer in India, with a 1.3 million cbm annual capacity across plants in Gujarat (Kheda, Umargaon, Kapadvanj) and Maharashtra (Wada). The company, which markets its products under the ‘NXTBLOC’ brand, is one of the few in the AAC industry to generate carbon credits. With over 2,000 completed projects and 1,500+ in the pipeline, The company’s clients include Lodha, Adani Realty, IndiaBulls Real Estate, DB Realty, Prestige, Piramal, Oberoi Realty, Tata Projects, Shirke Group, Shapoorji Pallonji Group, Raheja, PSP Projects, L&T, Sunteck, Dosti Group, Purvankara Ltd, DY Patil, Taj Hotels, Godrej Properties, Torrent Pharma, GAIL among others.

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