Dr SB Hegde, Professor, Jain University and Visiting Professor, Pennsylvania State University, United States of America, gives a detailed account of the use of waste glass as Pozzolana, a sustainable solution for cement production, in a two-part article.

The increasing demand for cement, coupled with growing environmental concerns, has led to a search for alternative materials that can reduce the carbon footprint of cement production. Waste glass, a significant environmental concern itself, has emerged as a promising alternative due to its pozzolanic properties.
This paper delves into the concept of utilising waste glass as a pozzolanic material in cement production, highlighting its benefits, challenges and potential for sustainable development based on the research and development work carried out by the author. This is part one of the study; part two will be featured in the consecutive issue of the magazine.

Generation and Availability of Waste Glass
On a global scale, this only amounts to a recycling rate of less than 35 per cent. Worldwide, around 130 million tonnes (Mta) of glass are currently produced annually.
India alone produces three million tonnes of glass waste annually, of which only 35 per cent is recovered, and the rest often ends up in landfills or down cycled into construction material aggregates. Glass is found in municipal solid waste (MSW), primarily in the form of containers such as beer and soft drink bottles; wine and liquor bottles; and bottles and jars for food, cosmetics and other products. India is one of the largest consumers of glass in the world, and as a result, it also generates a significant amount of waste glass. Waste glass, also known as cullet, can come from various sources such as bottles, jars, containers, windows and other glass products.
The availability and generation of waste glass in India depend on several factors, including population, consumption patterns, recycling infrastructure and waste management practices. Glass waste can be generated from residential households, commercial establishments and industries as well as construction and demolition activities. In recent years, there has been growing awareness about the importance of recycling glass waste in India. Recycling glass has several environmental benefits, such as reducing the consumption of raw materials, saving energy and reducing landfill waste.

Infrastructural requirement
To effectively use waste glass as a pozzolanic material in a cement plant, certain facilities and processes can be implemented. Here are some key facilities that can be created:

1. Glass Sorting and Preprocessing: A facility for sorting and preprocessing waste glass is essential to segregate glass by colour and removing contaminants such as paper, plastics and metals. Crushing or grinding equipment can be used to reduce the glass to a suitable particle size.
2. Glass Storage and Handling: Adequate storage facilities should be established to store the sorted and processed glass. It is important to protect the glass from moisture and other environmental factors that can affect its quality.
3. Glass Dosing System: A dosing system should be set up to accurately measure and control the amount of waste glass being added to the cement production process. This can involve automated feeders or other equipment to ensure a consistent and controlled addition of glass.
4. Glass Grinding or Milling Equipment: Depending on the desired fineness of the waste glass, a grinding or milling unit may be required to further reduce the particle size. This equipment can include ball mills, vertical roller mills, or specialised glass grinding mills.
5. Blending and Mixing Facilities: Cement plants typically have blending and mixing facilities where various supplementary cementitious materials, including waste glass, can be combined with other raw materials. This ensures homogeneity and uniformity in the cement production process.
6. Quality Control and Testing: Facilities for quality control and testing should be in place to assess the chemical and physical properties of the waste glass, as well as the performance of the cementitious mixtures incorporating the glass. This can include laboratory testing equipment and personnel trained in relevant testing methods.
   It’s important to note that the specific facilities required may vary depending on the scale of the cement plant and the volume of waste glass being processed. Detailed engineering studies and consultations in cement production and waste management can help determine the optimal design and layout of these facilities within a cement plant. Additionally, it is advisable to comply with relevant environmental regulations and obtain any necessary permits or approvals from statutory bodies in that particular country for handling and using waste glass within the cement plant.

The Fineness of Waste Glass
When waste glass is used as a supplementary cementitious material in cement production, it is important to consider the fineness or particle size distribution of the glass. The fineness of waste glass affects its reactivity and compatibility with
cement, which can impact the performance of the cementitious mixture.
The specific fineness requirements for waste glass can vary depending on the specific application, the type of cement being used, and the desired properties of the final concrete or mortar. However, in general, the waste glass particles should be finely ground to ensure effective pozzolanic or latent hydraulic reactions with the cement.
Here are some common guidelines for the fineness of waste glass used in cement:
• Particle Size Distribution: The waste glass particles should have a range of sizes to ensure good packing and fill the voids between cement particles. A typical particle size distribution for waste glass in cement applications is similar to that of cement, with a majority of particles passing through a 325 mesh (45 microns) sieve.
• Blaine Fineness: The Blaine fineness test is often used to measure the specific surface area of cementitious materials. The waste glass should generally have a Blaine fineness similar to or higher than that of cement. Typical values can range from 300 to 500 m²/kg or higher, depending on the application.
• Grinding or Milling: Waste glass may require grinding or milling processes to achieve the desired fineness. The grinding method can vary depending on the available equipment and the specific glass composition. Ball mills, vertical roller mills or specialised glass grinding equipment can be used.
• Gradation Control: It is important to control the gradation of waste glass during the grinding process. A well-controlled gradation can improve the flowability and workability of the cementitious mixture.
It is worth noting that the precise fineness requirements may vary depending on the specific standards, specifications, or guidelines established by statutory bodies of the particular country.

Attributes of Waste Glass as Pozzolana
Based on research and development investigations the following avenues are investigated for utilisation of waste glass.
• Pozzolanic Properties of Waste Glass: Pozzolanic materials, when combined with calcium hydroxide in the presence of water, react to form cementitious compounds. Waste glass, rich in amorphous silica, exhibits excellent pozzolanic properties. Through a process called pozzolanic reaction, waste glass can contribute to the strength, durability, and chemical resistance of cementitious materials.
• Environmental Benefits: Incorporating waste glass as a pozzolanic material in cement production offers significant environmental advantages. Firstly, it reduces the need for virgin raw materials such as limestone, thus conserving natural resources. Additionally, it mitigates the environmental impact associated with glass waste disposal, diverting it from landfills or incineration.
• Improved Concrete Performance: The use of waste glass as a pozzolanic material enhances the performance of concrete. Due to its pozzolanic activity, waste glass reacts with calcium hydroxide in the cement matrix, resulting in denser and more durable concrete. This leads to improved mechanical strength, reduced permeability, and increased resistance to chemical attack.
• Supplementary Cementitious Material: Waste glass can be used as a supplementary cementitious material (SCM) in cement production. When properly ground and processed, waste glass can replace a portion of cement without compromising the desired concrete properties. This substitution not only reduces cement consumption but also lowers the carbon dioxide emissions associated with cement production.
• Sustainable Development and Circular Economy: Utilising waste glass as a pozzolanic material aligns with the principles of sustainable development and the circular economy. It promotes resource efficiency, reduces waste generation, and contributes to a more sustainable construction industry. The integration of waste glass into cement production presents opportunities for collaboration between cement manufacturers, waste management companies, and regulatory bodies to develop innovative and eco-friendly solutions.

References

1. Utilisation of Waste Glass Powder in Concrete by P. Manoj Kumar,
   K. Sreenivasulu, and M. Srinivasulu Reddy, International Journal of Innovative Research in Science, Engineering and Technology, 2013.
2. Recycling of Waste Glass as a Partial Replacement for Fine Aggregate in Concrete Mix by W. A. Rahman, M. A. S. Al-gahtani,
   and M. A. K. El-Kourd, Journal of King Saud University – Engineering Sciences, 2010.
3. Mechanical and Durability Properties of Concrete Containing Glass Powder as Partial Replacement of Cement by A. Shayan and R. Xu, Construction and Building Materials, 2004.
4. Properties of Glass Concrete Containing Fine and Coarse Glass Aggregates by Z. Feng, S. Xie, and Y. Zhou, Journal of Materials in Civil Engineering, 2011.

ABOUT THE AUTHOR
Dr SB Hegde, Professor, Jain University and Visiting Professor, Pennsylvania State University, United States of America.