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Making our Concrete Jungles More Environmentally Friendly


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It goes without saying that water is the most widely used material globally. It is surprising, however, to know that cement is the next, even when taking into account it is the key ingredient in concrete, our most used building material.

Cement accounts for a staggering eight per cent of the world’s CO2 emissions. For every tonne produced in Australia, 0.82 tonnes of CO2 is released into the atmosphere. Taking that statistic to a global scale, where more than four billion tonnes of cement is produced, which equates to a staggering amount of greenhouse gases - with CO2 contributing around 70 per cent of the world’s forcing greenhouse gases overall.

Cement accounts for a staggering eight per cent of the world’s CO2 emissions. 

The gases are produced from cement by a combination of the energy and heat requirements in the manufacturing process, and the calcination process in manufacturing - that is where the limestone (calcium carbonate) in cement is heated to become quicklime or calcium oxide, emitting large amounts of CO2 in the process (as much as half of the total CO2 produced in the manufacturing process. The construction sector has been making cement this way (Portland cement) since the nineteenth century, and it has become the industry standard.

With the Paris Climate change agreement committed to reducing global warming to less than 2℃, every industrial sector should be looking at ways to contribute. With almost ten per cent of carbon emissions being created by the cement industry, much research has gone into more environmentally friendly ways to green the concrete jungle.

Beyond Zero Emissions (BZE) is one of Australia’s most respected climate change think tanks producing independent research demonstrating that zero emissions is already achievable and affordable. It has just published its report Zero Carbon Industry Plan Rethinking Cement investigating strategies to reduce and ultimately eliminate cement emissions. The report has come up with five strategies. The first three deliver a zero carbon Australian cement industry in only a decade, by changing the way cement is made. The last two strategies would enable Australia to exceed zero emissions, by changing the way we approach building and turning our built environment into a carbon sink.

Strategy one involves replacing 50 per cent of conventional concrete with geopolymer cement. The production of geopolymer cement doesn’t create any greenhouse gases making that a zero emissions win. Geopolymer cement is produced from ingredients other than limestone, such as fly ash, slag, or clay. Given Australia already has about 400 million tonnes of fly ash as a waste product from the coal industry, BZE estimates using just a quarter of this amount will be sufficient for 20 years’ supply.

The production of geopolymer cement doesn’t create any greenhouse gases making that a zero emissions win. 

The second strategy involves blending regular cement with other materials to reduce its carbon intensity. It proposes increasing the proportion of replacement material to 70 per cent, using fly ash, slag, clay and ground limestone. These blends have already had success around the world and is available in Australia, but the uptake has not been high.

BZE Project director and lead author of the report, Michael Lord explains that the reluctance of the construction and cement industry to embrace the first two readily available strategies comes down to conservatism and lack of incentive: “Portland cement is tried and tested. If a job specifies it, no-one will ask questions, whereas to specify geopolymer or high blend, they will need to make a case to justify that decision. There is no standard yet written for geopolymer cement, making it difficult to make a case beyond the environmental one.”

Lord also highlights lack of supply: “None of the three major cement companies in Australia supplies geopolymer, and only Boral produces a high blend version. With a shortage of major suppliers, builders would need to rely on minor suppliers who simply don’t have the clout.” 

The third strategy proposes a new technology whereby waste carbon is captured and sealed in the rock. It is a new technology called mineral carbonation, and can capture the emissions from the production of Portland cement. Using this technology could result in as much as 90 per cent of cement kiln emissions from being released into the atmosphere. 

The fourth strategy is simply to use less cement. It involves rethinking design to use concrete more efficiently and employ other materials in lieu of concrete, such as timber. By employing Strategy 4, the BZE report estimates overall consumption could be reduced by around 15 per cent within the next decade.

The fifth and perhaps most exciting strategy is to produce “carbon negative cement”. Theoretically, it is possible by using magnesium oxide in place of quicklime. The compound can absorb CO2 from the air once water is added to the cement and developer Novacem claims that a tonne of its cement creates a negative footprint of 0.6 tonnes of CO2.

The fifth and perhaps most exciting strategy is to produce “carbon negative cement”. 

“Carbon Negative cement is still in the research and development stages, and not yet available,”says Michael Lord. “Australian company Calix now owns the technology for carbon negative cement, but has not yet released any research.”  

The BZE report outlines ways to increase industry adoption of greener concrete, suggesting it is a combination of Government and Industry responsibility. It further suggests that a powerful stimulus would be a national policy that outs a price on carbon emissions, including cement imported into Australia. The report goes on to say the Australian Government should introduce a progressive reduction target to reduce the intensity of cement.

“We do have the support of the Australian Infrastructure Council of Australia (ISCA) which rates sustainability on infrastructure jobs valued above $50 million,” says Lord. “In Victoria and NSW, ISCA and Green Star ratings have driven the increase in high blend cement usage.” 

The report also outlines a strategy to support progressive targets by public investment into research and deployment of low carbon cements, including incentives and/or regulations to promote the use of stockpiled fly ash and other waste materials, such as waste glass, red mud (waste from aluminium industry), and bagasse ash (sugar cane waste pulp) in cement manufacturing.

BZE has presented its report findings to around 20-30 industry heavyweights and government bodies since its release and has been encouraged by a positive reaction and feedback from all parties. It now remains to be seen whether the uptake in more environmentally friendly cement increases.

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