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The most manufactured product on the planet in terms of volume is Portland cement-based concrete. Its reliability, cost-effectiveness, versatility and widespread availability have made a fundamental component of almost all building projects.
However, as sustainability emerges as a vital criterion for the next generation of building materials, Portland cement is coming under pressure to update due to its unsustainable production practices.
Geopolymer foam concrete has become increasingly popular mainly due to its property as an excellent thermal insulator, allowing buildings in cold regions to retain heat and therefore become more energy efficient.
Importantly, the production of geopolymer foam concrete does not involve the same unsustainable processes as that of Portland cement-based concrete. Therefore, it is believed to be a potential global solution to the unsustainability of the concrete industry.
The Sustainability of Concrete Production
Concrete production is considered to be an unsustainable process due to the incredibly high production volumes needed to meet an ever-rising growing demand as urbanization continues across the planet.
These high production volumes, over 4,000 million tonnes annually, are leading to the consumption of vast amounts of energy, resulting in the emittance of large quantities of greenhouse gases as well as significantly contributing to dust pollution.
In 2019, 4-8% of the world’s carbon dioxide emissions were attributed to the production processes of concrete. If the concrete industry were a country, it would be the world’s third-biggest contributor to carbon dioxide emissions.
Regulations and criteria surrounding building materials are increasingly focusing on acting to reduce the environmental impact of the concrete industry. As industries become more aware of the reality of global warming and its detrimental effects on the planet, initiatives are being set to tackle emissions in every sector.
Given concrete’s significant contribution to greenhouse gas emissions coupled with the considerable volume of product being produced annually, scientists have long been exploring how to make production more environmentally friendly. The solution, it seems, may come in the form of geopolymer-based foam concrete.
Using Geopolymers in Concrete
Geopolymers have been explored since the 1970s and became the term used to describe a group of materials that are completely inorganic and form covalently bonded, long-range, non-crystalline networks. While they were first used for their fire-resistant properties, they have since been developed for a wide range of construction applications.
Importantly, the production processes involved in making geopolymers are less energy-dependent and produce fewer carbon dioxide emissions. This means that the methods are more sustainable than those of Portland cement-based concrete production.
In addition, fly ash, one of the primary raw materials of geopolymer synthesis, is a waste product of the coal industry, meaning that the process helps to reduce the environmental impact of the fossil fuel industry.
In recent years, scientists have developed methods to combine geopolymer technology with foam concrete and created a product that has a reduced carbon footprint as well as the beneficial properties of foam concrete.
Foam concrete is a lightweight material that is constructed with a cementitious binder with void space and sometimes a fine aggregate. The binder used is generally OPC-based and is mixed with other components to give it different characteristics. To replace the cement component, fly ash and GBFS are also typically added. The cost of foam concrete production is also sometimes reduced by adding in granitic limestone and silica fines.
An essential step of foam concrete production is controlling the size, distribution, and nature of the voids. These voids are either produced by endogenous gas generation, or by introducing a large volume fraction of air bubbles. These different processes will result in different sizes and distributions of bubbles being dispersed in the mixture, which impacts the properties of the geopolymer foam concrete. One of these essential properties is the thermal characteristics of the concrete.
The Thermal Properties of Geopolymer Foam Concrete
The reason for the rise in the popularity of foam concretes has mostly been due to their good thermal insulation properties. Foam concretes with geopolymers have been proven to have poor thermal conductivity, meaning that they retain the heat energy that is transferred to them. This is important in the world’s colder regions because it allows buildings to retain heat, resulting in a reduction in reliance on heating systems and allowing the buildings to be more energy-efficient.
This is another critical factor in tackling the climate crisis. There is now a significant trend in developing buildings that use less energy and emit fewer emissions. The loss of heat through building walls is a major contributor to excessive energy use. Using concretes such as geopolymer foam concretes enables less heat to be lost, which effectively tackles this problem.
Reducing Emissions with Geopolymers in Foam Concrete
Overall, the use of geopolymers in foam concrete is allowing the production of concrete to be more sustainable, reducing its impact on the environment by lowering the emissions associated with the concrete industry.
In addition, the use of this type of concrete is enabling buildings to be more energy-efficient, which is helping countries in colder regions to significantly reduce their energy use and, therefore, reduce their greenhouse gas emissions.
References and Further Reading
Amran, Y., Farzadnia, N. and Abang Ali, A. (2015). Properties and applications of foamed concrete; a review. Construction and Building Materials, 101, pp.990-1005. https://www.researchgate.net/publication/283653165_Properties_and_applications_of_foamed_concrete_a_review
Climate change: The massive CO2 emitter you may not know about. Available at: https://www.bbc.com/news/science-environment-46455844
Concrete: the most destructive material on Earth. Available at: https://www.theguardian.com/cities/2019/feb/25/concrete-the-most-destructive-material-on-earth
Namsone, E., Šahmenko, G. and Korjakins, A. (2017). Durability Properties of High Performance Foamed Concrete. Procedia Engineering, 172, pp.760-767. https://www.sciencedirect.com/science/article/pii/S1877705817306264
Zhang, Z., Provis, J., Reid, A. and Wang, H. (2014). Geopolymer foam concrete: An emerging material for sustainable construction. Construction and Building Materials, 56, pp.113-127. https://www.researchgate.net/publication/260314289_Geopolymer_foam_concrete_An_emerging_material_for_sustainable_construction
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