Cutting Emissions By Cutting Clinker

In recent years, cement additives have played a crucial role in lowering GHG emissions by enabling significant clinker reduction in cement. These additives, evolved from traditional grinding aids, are chemical agents introduced during the grinding process to enhance mill efficiency and improve the performance of the final product. Among their various benefits, cement additives notably enhance strength development at all ages, facilitating clinker reduction in cement production.

This case study explores the practical application of cement additives, demonstrating their effectiveness in reducing clinker content and fostering sustainable cement manufacturing.

Cement production and strategies for reducing GHG emissions

Cement production is broadly categorised into two key stages: clinker production and cement grinding. During the clinkerisation stage, proportioned raw materials, primarily limestone, are finely ground and calcined in an in-line calciner before entering the kiln. At temperatures of approximately 1450°C, the raw material undergoes chemical transformation into hydraulic active clinker. This stage is responsible for the highest carbon dioxide (CO₂) emissions, due to the decomposition of calcium carbonate (CaCO₂) into calcium oxide (CaO) releasing CO₂ into the atmosphere. Additionally, fuel combustion required to sustain these high temperatures further contributes to emissions, including CO₂, sulfur oxides (SOx), and nitrogen oxides (NOx).

Following clinkerisation, the clinker is ground with gypsum to produce ordinary portland cement (OPC), a process that primarily relies on electrical energy.

Over the years, the cement industry has made significant progress in reducing GHG emissions by optimising production processes and adopting advanced high-efficiency technologies, like improved quality control systems, high efficiency grinding, automating process control, high efficiency separators, and efficient clinker cooling. However, clinker reduction remains the most effective approach to achieving substantial emission reductions. Recognising this, organisations such as the National Council for Cement and Building Materials (NCB) in India, along with regulatory bodies like the Bureau of Indian Standards (BIS), have introduced and promoted specifications for blended and composite cements with lower clinker content than OPC.

Blended cements in India account for approximately 73% of total cement production, including various types such as:

• Portland pozzolana cement (PPC): as per IS 1489 (Part 1): 2015, PPC allows for 15 – 35% fly ash addition.
• Portland slag cement (PSC): according to IS 455: 2015, PSC permits 25 – 70% slag addition.
• Portland composite cement (PCC/CC): this type contains 35 – 65% clinker.
• Limestone calcined clay cement (LC3): the latest blended cement type introduced by BIS under IS 18189-2023, LC3 has a clinker content of 50 – 80%.

These blended cements offer substantial environmental benefits. Indian cement industries have been producing these types for a long time. However, achieving maximum clinker reduction remains challenging. This is due to the clinker's ability to integrate supplementary cementitious materials (SCMs), such as fly ash, ground granulated blast furnace slag (GGBS), and limestone, and vice-versa, while still maintaining the required strength and performance parameters of the cement.

To bridge this gap, cement additives play a crucial role in enabling clinker reduction without compromising cement quality. These chemical accelerators contain organic components such as triethanolamine, triisopropanolamine, and crude glycols, along with other hydration-modifying agents which enhance the hydration of clinker phases and reactivity of SCMs. Some advanced additives incorporate polycarboxylate ethers (PCEs), though further research is needed to fully qualify them as cement additives.

By leveraging cement additives, manufacturers can achieve lower clinker content, contributing to sustainable cement production and supporting the industry's commitment to GHG reduction goals.

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Read the article online at: https://www.worldcement.com/special-reports/14082025/cutting-emissions-by-cutting-clinker/