Concrete ranks among the most common and popular building materials. It is a symbol of modern living and can be moulded into structural masterworks.
Yet cement, concrete’s chief ingredient that blends the other sand and gravel to lend it its famous strength, is the source of approximately 8 per cent of the world’s carbon dioxide (CO2) emissions.
Slicing the emissions in cement is a challenge, as the emissions emanate from an unavoidable chemical reaction during its manufacture. Exchanging cement for other low carbon binding ingredients is also tough, as nothing seems to replace cement.
In 2021, the Global Cement and Concrete Association launched a roadmap to decarbonise the universal industry by 2050, and Cement, Concrete and Aggregates Australia (CCAA) and other organisations have requested a report regarding decarbonisation pathways for Australia’s concrete and cement business.
Materials expert Jonas Bengtsson, chief executive officer and co-founder of sustainability consultancy Edge, says that major change will be needed to implement low carbon concrete technology—as concrete itself cannot be replaced.
Concrete manufacturers strive to lower the per cubic metre carbon intensity of the product. Yet a good number of emissions happen up the supply chain in the clinker production. Elsewhere in the supply chain, builders can be held accountable for spillage and wastage of the grey mixture.
The design and engineering profession could specify a lighter supply of concrete in structures and infrastructure and developers should think of the lifespan of structures and design them in a manner that they can be adapted for reuse.
For instance, Bengtsson says car parks can be designed with higher ceilings so that they can be converted into office space or apartments as opposed to being demolished.
The key, he says, is to build a bit smarter for adaptive reuse. The use of lower carbon materials is important, as is hybrid structures made of concrete and steel coupled with lower carbon materials like timber.
George Agriogiannis, chief executive officer at Holcim Australia, which possesses a Science based Target and is providing a carbon neutral concrete product (attained through offsets), cites much demand in the market for lower carbon materials. He says carbon is on the mind of every building client.
A pair of major ticket emissions-intensive processes are involved in cement manufacturing: The usage of fossil fuels in heat processing, which accounts for 40-45 per cent of emissions, and the unavoidable chemical reaction known as calcination accounting for about 50 per cent of emissions where calcium carbonate morphs into lime and carbon dioxide.
Cement Concrete & Aggregates Australia chief executive officer Ken Slattery says that the industry relies on reducing emissions during processing through the use of alternative fuels, new kiln technologies that utilise less fuel, and enhanced grinding and processing activities.
He says the industry has attained a 25 per cent reduction in carbon emissions since the turn of the century. But it’s not getting any easier.
The problem of fighting clinker emissions, he says, involves the addition of fly ash (a bi-product from burning coal) and ground granulated blast furnace slag (a bi-product from steelmaking).
Dr Louise Keyte, Boral general manager – technology execution and co-director of the UTS Boral Centre for Sustainable Building, states the main challenge of cement replacements revolves around strength development. She cites a challenge in that, when cement is replaced by SCMs, they react at a slower speed.
Keyte says this delay poses challenges for tighter building timelines and budgets. For this reason, she says, innovation is critical.
The company offers a myriad of low carbon concrete options, each right for varying applications, attaining as high as a 50 per cent reduction in cement. One of Keyte’s research priorities is to improve on this score–reducing cement content to 70 per cent.
She also calls for an overhaul in Australia’s restrictive standards and specifications for concrete. Thus guaranteeing that fit-for-purpose concrete is used for roads, buildings and other critical infrastructure.
Holcim Australia’s Agriogiannis states that governments, state governments especially, could devise overarching procurement policies that prefer low carbon materials. He says, ultimately, that change is possible.
Civil Engineering expert and Associate Professor at Macquarie University Sorn Vimonsatit and her colleagues at Macquarie University, who is hosting the SmartCrete CRC, have attained $400,000 to create a polymer concrete using waste latex paint. Vimonsatit cites the importance of the circular economy to create employment and social sustainability benefits, also citing hydrogen power trucks as an option. The best option, in her view, is for industry, academia and government to collaborate to resolve the decarbonisation and sustainability challenges facing concrete, sharing sustainable knowledge and creating a roadmap for the future.
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