Geopolymers: An alternative to Portland cement

Geopolymer concrete path laid at Curtin University, Bentley campus

Portland cement is the most common type of cement in general usage. Portland cement and similar materials are made by heating limestone with clay or sand and grinding the product to form cement powder. When mixed with water the powder becomes, over time, a hydrated solid.

The manufacture of Portland cement requires the burning of large quantities of fuel, typically coal or natural gas, which, along with impurities contained in the limestone, can result in significant emissions of pollutants including:

• greenhouse gases such as carbon dioxide, carbon monoxide, sulfur dioxide and nitrogen oxides
• particulates
• volatile organic compounds.

Geopolymer concrete negates the need for Portland cement as a binder. Instead, waste materials such as fly ash are activated by alkaline liquids (most often at temperatures below 50 degrees Celsius) to create the cement. Hence, concrete can be produced without the need for large quantities of fuel, making it far more energy efficient and avoiding much of the environmental pollutants associated with traditional Portland cement production.

Applications of geopolymer cements

Geopolymer properties can be varied to produce materials that behave as adhesive rubber or as a very hard solid. This allows geopolymers to be useful as a key ingredient for a wide range of applications such as:

• encapsulation of toxic waste materials
• high strength and high performance concrete building products
• high toughness geopolymer/ceramic fibre composites
• fire resistant products or refractories
• insulator components.

Understanding the microstructure of geopolymer materials is critical to predicting and tailoring material properties for particular applications. Therefore, current CMR research, supported by the Cooperative Research Centre for Sustainable Resource Processing (CRC-SRP), is aimed at fully characterising the range of geopolymers that can be created and understanding the reactions that occur during geopolymer cement formation and subsequent processing.