on June 6th, 2024

Cement production contributes 8% to global carbon emissions ( CO2), and as the demand for concrete grows, engineers have discovered a method to cut these emissions significantly.

In 2022, coal-fired power plants produced over 1.2 billion tonnes of coal ash. In Australia, coal ash constitutes nearly 20% of all waste and will be plentiful for years to come, even as the shift to renewable energy continues.

Cement production is responsible for a significant portion of global carbon emissions, and the rising demand for concrete exacerbates this issue.

Dr. Ana Evangelista, a civil engineering lecturer and course coordinator at the Engineering Institute of Technology emphasized, “The cement industry recognizes the urgency of climate action and is committed to developing and deploying new technologies to reduce our CO2 footprint.”

To tackle both problems, engineers at the Royal Melbourne Institute of Technology (RMIT) have collaborated with AGL’s Loy Yang Power Station and the Ash Development Association of Australia to replace 80% of the cement in concrete with coal fly ash.

Dr. Chamila Gunasekara, the lead on the RMIT project, stated that this innovation marks a major step forward, as current low-carbon concretes typically substitute no more than 40% of cement with fly ash.

“Our use of nano additives changes the concrete’s chemistry, enabling the inclusion of more fly ash without sacrificing performance,” said Gunasekara, from RMIT’s School of Engineering.

New Uses for Pond Ash

Thorough lab studies have demonstrated that the team’s approach also works with ‘pond ash’—low-grade ash from coal slurry storage ponds at power plants—with minimal pre-processing.

Large concrete beam prototypes made with both fly ash and pond ash have met Australian Standards for performance and environmental impact.
“It’s promising that initial results indicate similar performance with lower-grade pond ash, potentially unlocking a vast, underutilized resource for cement replacement,” Gunasekara said.

Pond ash is less commonly used in construction than fly ash due to its different properties. There are vast amounts of ash waste in dams across Australia and globally. These ash ponds pose environmental risks, and repurposing this ash in construction materials on a large scale would be a significant achievement.

Aussie Engineers Reduce Cement-Produced Carbon Emissions: Modeling Ensures Concrete’s Durability

A pilot computer modeling program, developed by RMIT in collaboration with Dr. Yogarajah Elakneswaran from Hokkaido University, has been used to forecast the long-term performance of these new concrete mixtures.

Dr. Yuguo Yu, an expert in virtual computational mechanics at RMIT, explained that a major challenge has been predicting how new materials will perform over time. “We’ve developed a physics-based model to predict the long-term performance of low-carbon concrete, allowing us to refine and optimize mixes based on these insights,” Dr. Yu said.

This innovative approach, published in the journal Cement and Concrete Research, details how different ingredients in the new low-carbon concrete behave over time.

“For instance, we can observe how quick-setting nano additives enhance performance in the early stages, offsetting the slower-setting fly ash and pond ash,” Gunasekara said, adding that the inclusion of ultra-fine nano additives significantly improves the material by increasing its density and compactness.

This modeling capability, which can be applied to various materials, represents a critical advancement in digitally assisted design and construction. By utilizing this technology, the team aims to build trust among local councils and communities in adopting new low-carbon concrete for diverse applications.

Key Environmental Impacts of Concrete

Concrete has its pros and cons. It is a versatile material widely used in construction, but it also poses several environmental challenges.

Here are some examples of the positive and negative impacts of concrete in our daily lives:

High Carbon Emissions and Topsoil Damage

• Concrete production accounts for 4-8% of global CO2 emissions, mainly from cement manufacturing, a major source of carbon dioxide.

• The use of concrete in construction damages topsoil, which is the earth’s most fertile layer.

Runoff, Flood Control, and Heat Reduction

• Concrete surfaces can cause surface runoff, leading to soil erosion, water pollution, and flooding.

• Conversely, concrete is effective in flood control through dams, diversions, and deflection of floodwaters.

• Light-colored concrete can reduce the urban heat island effect due to its reflective properties, though natural vegetation is more beneficial.

Pollution, Health Risks, and Recycling

• Demolition of concrete structures can release dust that pollutes the air and poses health risks.
• Some concrete additives can be toxic or radioactive, and wet concrete is highly alkaline, requiring careful handling.

• Recycling of concrete is on the rise due to environmental awareness, regulations, and cost benefits, reducing reliance on alternative materials like wood, which sequesters carbon naturally.

A Solid Foundation for Future Construction

The development of environmentally friendly cement and concrete marks a pivotal moment in the pursuit of sustainable construction practices. As global carbon emissions continue to rise, innovations such as the substitution of cement with coal fly ash provide a crucial avenue for reducing the environmental impact of one of the most widely used construction materials.

Dr. Ana Evangelista noted, “From the cement industry perspective, the cement sector uses slag, a by-product of steel manufacturing, as a partial substitute for limestone in cement production. They developed a new process model to predict the impact on cement quality, aiming to optimize this method for lower emissions.”

Adopting these greener alternatives is essential for future-proofing global infrastructure. Engineers now have the tools and knowledge to create durable, high-performance concrete with a substantially lower carbon footprint. The integration of underutilized resources like pond ash further exemplifies the potential for sustainable innovation within the construction industry.

Additionally, Dr. Evangelista highlighted a key area of research: “Finding alternative materials to replace clinker, the main component of cement with high CO2 emissions during production.”

A 2023 study published in Clean Technologies and Environmental Policy explored using supplementary cementitious materials (SCMs) to reduce clinker content in blended cement.

In Australia, another promising avenue is geopolymer cement, which can be made from industrial waste materials and requires less energy to produce compared to traditional Portland cement.

Ultimately, the efforts of the RMIT team highlight the critical role of engineering in combating climate change and promoting environmental stewardship. As we move towards a more sustainable future, these developments will be instrumental in building resilient and eco-friendly infrastructure worldwide.

References

What is green concrete?

Green concrete recycling twice the coal ash is built to last

Environmental impact of concrete

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