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Blog 5: From Lattes to Concrete: The Surprising Strength of Coffee Waste
Imagine sipping your morning latte and knowing that the spent coffee grounds from your cup could one day form the foundation of your home. This idea may soon become a reality, thanks to a groundbreaking study by engineers at RMIT University in Melbourne, Australia.
Motivation Behind this Innovation
The driving force behind this groundbreaking study was the alarming amount of organic waste ending up in landfills, contributing significantly to greenhouse gas emissions. In Australia, approximately 6.87 million tonnes of organic waste are dumped in landfills annually, accounting for 3% of the country's total greenhouse gas emissions. Recognizing the urgent need to address this issue, the research team at RMIT University decided to shift their focus towards developing innovative solutions that could divert this waste from landfills and transform it into a valuable resource. Interestingly, the idea to start with coffee grounds emerged during a team meeting over a cup of coffee, highlighting the serendipitous nature of scientific discovery.
The Coffee Waste
Coffee is one of the most widely consumed beverages in the world, with millions of cups enjoyed daily. However, this popularity comes at a significant environmental cost. In Australia alone, around 75,000 tonnes of spent coffee grounds end up in landfills each year, contributing to a growing waste problem. Globally, this number skyrockets to a staggering 10 billion kilograms of coffee waste annually. As the world becomes increasingly focused on sustainability and waste reduction, researchers are constantly seeking innovative ways to repurpose these waste materials and mitigate their environmental impact.
From Coffee Waste to Biochar
Coffee is one of the most widely consumed beverages in the world, with millions of cups enjoyed daily. However, this popularity comes at a significant environmental cost. In Australia alone, around 75,000 tonnes of spent coffee grounds end up in landfills each year, contributing to a growing waste problem. Globally, this number skyrockets to a staggering 10 billion kilograms of coffee waste annually. As the world becomes increasingly focused on sustainability and waste reduction, researchers are constantly seeking innovative ways to repurpose these waste materials and mitigate their environmental impact.
Coffee Biochar for a Stronger Concrete
When incorporated into concrete, the coffee-derived biochar proved to have remarkable effects. At an optimal replacement level of 15% by volume of sand, the biochar increased the compressive strength of the concrete by an impressive 29.3%. The porous nature of the biochar allows it to absorb water and contribute to the internal curing of the concrete, leading to enhanced strength development.
The Role of Pyrolysis Temperature
The researchers found that the temperature at which the biochar is produced plays a crucial role in its effectiveness. Biochar created at 350°C provided the best results, while that produced at 500°C showed a decrease in strength due to its more fragile structure. This highlights the importance of fine-tuning the pyrolysis process to maximize the benefits of the biochar.
Environmental and Economic Benefits
- ~30% increase in concrete strength
- This significant increase in strength can be leveraged to reduce the required cement content
- Creates a potential for the 100% uptake of this waste material for concrete applications
- This waste to resource transformation creates a potential for diverting this waste from going to landfills, promoting sustainability, and closed loop circular economy.
Research Team
Rajeev Roychand, Shannon Kilmartin-Lynch, Mohammad Saberian, Jie Li, Guomin Zhang, Chun Qing Li
Publication Reference
Transforming spent coffee grounds into a valuable resource for the enhancement of concrete strength is published in the Journal of Cleaner Production (DOI: 10.1016/j.jclepro.2023.138205)
Blog 4: Rubber Meets the Road: Transforming Tires into Sustainable Concrete
In a world where sustainability is no longer a choice but a necessity, engineers have achieved the remarkable feat of creating concrete that completely replaces conventional aggregates, such as gravel and crushed rock, with rubber derived from discarded tires.
A Pressing Issue
Every year, billions of waste tires end up in landfills, posing significant environmental challenges. These non-biodegradable materials not only occupy valuable land space but also contribute to air and water pollution when burned or stockpiled. The need for effective recycling methods has never been more urgent.
From Waste to Resource
Enter the visionary team of researchers from RMIT University in Melbourne, Australia. Led by Dr. Mohammad Momeen Ul Islam, they have developed an ingenious method that transforms waste tire rubber into a valuable resource for the construction industry.
Their innovative approach involves replacing conventional coarse aggregates in concrete entirely with rubber particles from end-of-life tires. By employing a novel compression casting technique, they have successfully created structural lightweight concrete with remarkable mechanical properties.
Strength and Sustainability
The rubber concrete developed by the RMIT team boasts a compressive strength of up to 97% higher than traditional rubberized concrete. This significant improvement in strength is achieved through the compression casting process, which minimizes the gaps between the rubber particles and the cement matrix, resulting in a denser and more durable material.
Moreover, the carbon footprint of this rubber concrete is substantially lower compared to conventional concrete. By utilizing waste tires, which would otherwise end up in landfills, the researchers have found a way to reduce the environmental impact of construction while also conserving natural resources.
A Greener Future
The potential applications of this rubber concrete are vast, ranging from residential construction to infrastructure projects. Its lightweight nature and impressive strength make it an attractive option for builders seeking sustainable alternatives to traditional concrete.
As the world grapples with the urgent need to combat climate change and reduce waste, innovations like rubber concrete offer a glimmer of hope. By turning waste into a valuable resource, we can pave the way to a greener, more sustainable future.
The research conducted by Dr. Islam, Dr. Li, and their team at RMIT University is a testament to the power of scientific ingenuity in addressing global challenges. As more industries embrace such eco-friendly solutions, we can look forward to a world where sustainability is not just a buzzword but a way of life.
Research Team
Mohammad Momeen Ul Islam, Jie Li, Yu-Fei Wu, Rajeev Roychand, Mohammad Saberian
Publication Reference
Design and strength optimization method for the production of structural lightweight concrete: An experimental investigation for the complete replacement of conventional coarse aggregates by waste rubber particles is published in the Journal of Resources, Conservation and Recycling (DOI: 10.1016/j.resconrec.2022.106390)
Blog 3: Disposable PPE waste makes concrete stronger by up to 22%
Researchers at RMIT University have found a way to give new life to disposable personal protective equipment (PPE) waste by using it to strengthen concrete, offering a creative solution to the challenge of managing the surge of pandemic-related plastic waste.
The environmental impact of PPE waste
The COVID-19 pandemic has not only strained healthcare systems worldwide but has also created a new stream of plastic waste in the form of discarded PPE. Globally, it is estimated that 129 billion face masks and 65 billion gloves are used each month. This surge in PPE waste has led to increased littering, with discarded items ending up in landfills and oceans, contributing to the growing problem of microplastic pollution.
Recycling PPE waste in concrete
To tackle this environmental challenge, the RMIT research team, led by Dr Shannon Kilmartin-Lynch, has investigated the potential of incorporating shredded PPE waste into structural concrete. By repurposing these materials, they aim to divert waste from landfills and reduce the environmental footprint of the construction industry.
- Nitrile gloves
- Polypropylene face masks
- Isolation gowns
Concrete Strengthening Mechanism
The researchers found that incorporating shredded PPE waste into concrete helps in improving its strength properties. The team attributed these improvements to the strong bond formed between the shredded PPE materials and the cement matrix, as observed through scanning electron microscopy. This strong bond allows for better stress transfer and crack bridging within the concrete mixture.
- Up to 22% higher strength with shredded nitrile gloves
- Up to 17% higher strength with shredded face masks
- Up to 15.5% higher strength with shredded Isolation gowns
Towards a circular economy
The research conducted by the RMIT team demonstrates the potential for a closed loop circular economy approach in the construction industry, where waste materials are repurposed as valuable resources. By incorporating PPE waste into concrete, not only can we reduce the environmental impact of the pandemic but also create a more sustainable built environment.
As the world continues to grapple with the challenges posed by COVID-19, it is crucial to find innovative solutions to manage the waste generated by the pandemic. The work of Dr. Li and his team at RMIT University serves as an inspiring example of how creative thinking and scientific research can help us build a more sustainable future.
Research Team
Shannon Kilmartin-Lynch, Rajeev Roychand, Mohammad Saberian, Jie Li, Guomin Zhang
Publication References
Application of COVID-19 single-use shredded nitrile gloves in structural concrete: Case study from Australia is published in the Journal of Science of The Total Environment (DOI: 10.1016/j.scitotenv.2021.151423)
Preliminary evaluation of the feasibility of using polypropylene fibres from COVID-19 single-use face masks to improve the mechanical properties of concrete is published in the Journal of Cleaner Production (DOI: 10.1016/j.jclepro.2021.126460)
A sustainable approach on the utilisation of COVID-19 plastic based isolation gowns in structural concrete is published in the Journal of Case Studies in Construction Materials (DOI: 10.1016/j.cscm.2022.e01408)
Blog 2: High durability zero cement concrete beats corrosion and resists fatbergs
Researchers from RMIT University have pioneered an innovative zero cement concrete, wielding the power to eliminate corrosion and thwart the formation of fatbergs, thus extending the lifespan of infrastructure like never before.
The problem
Cement concrete, the backbone of our urban infrastructure, not only comes with high carbon footprint, but in the realm of sewage infrastructure, hides a dirty secret. The cement that binds the sand and gravel has a weak link i.e., free lime – a byproduct of cement hydration, that is released into the concrete. In the acidic sewage environment, the concrete rich in free lime becomes a vulnerable target to the corrosive acids, silently corroding the very core of sewage pipes. An even grimmer fate awaits on the inside of the pipes, where the same free lime reacts with fats, oils, and greases (FOGs) in the sewage to form giant, pipe-clogging "fatbergs". Maintaining and upgrading the sewage network comes with high costs and disruptions to the general public. With annual maintenance expenses reaching up to $15 million in Australia, tens of millions in the United Kingdom, and figure skyrocketing to billions in the USA, the financial burden on governments and taxpayers is undeniable.
Deciphering the Code
The team of researchers, led by Dr Rajeev Roychand, have cracked the code, unveiling how free lime, the hidden instigator of concrete corrosion, also plays a pivotal role in the formation of fatbergs. Furthermore, they have demonstrated how this innovative zero cement concrete, free from this inherent vulnerability, can play a crucial role in addressing these challenges.
The Innovation
By harnessing a cocktail of industrial byproducts like fly ash and slag, and fortifying it with nano-silica particles, the researchers have conjured up a concrete capable of withstanding the corrosive conditions inside sewers, while also help in preventing the sewers' worst enemies: corrosion and fatbergs. This innovation has the potential to revolutionize the way we build and maintain our infrastructure.
A sewer pipe dream come true?
While the researchers have shown it's possible to eliminate Portland cement from concrete sewage pipes, the long-term performance of this zero-cement concrete in real-world conditions still needs to be proven. Nevertheless, the study points the way to a future where concrete infrastructure is not only greener, but also lasts longer with less maintenance - a win for sustainability on multiple fronts.
Research Team
Rajeev Roychand, Jie Li, Saman De Silva, Mohammad Saberian, David Law, Biplob Kumar Pramanik
Publication Reference
Development of zero cement composite for the protection of concrete sewage pipes from corrosion and fatbergs is published in the Journal of Resources, Conservation & Recycling (DOI: 10.1016/j.resconrec.2020.105166)
Blog 1: Double shot at circular economy - Steel slag soaks up toxins, then boosts concrete strength
Imagine a world where the by-products of steelmaking not only clean up wastewater but also contribute to creating stronger, more resilient concrete.
The Innovation
An inter-disciplinary research team at RMIT, jointly led by Dr. Rajeev Roychand (Civil) and Dr. Biplob Kumar Pramanik (Environmental), have cracked the code, revealing the power of steel slag in a zero-waste strategy that not only benefits the environment but also boosts the circular economy. This innovative approach not only removes harmful chemicals from municipal wastewater but transforms the chemical and mineralogical composition of the slag, making it a star performer in enhancing concrete strength. It's a double win for sustainability—cleaner water and stronger structures, all from a by-product of steel manufacturing process!
Transformation of Slag Chemistry after Water Treatment
The most dramatic change was the massive increase in iron content after filtration. XRF showed that iron oxides shot up from a mere 0.7% in the original slag to a whopping 30.5% post-sewage treatment. This iron was present in new crystalline compounds like calcium aluminum iron oxide and wuestite, which were completely absent in the raw slag. Interestingly, common slag minerals like akermanite-gehlenite were no longer detectable after wastewater filtration, likely transforming into amorphous phases. The sewage-soaked slag also formed new phosphate-containing crystals, suggesting that some of the phosphorus removed from the wastewater was chemically incorporated into the slag.
The Microscopic Detective Work
Scanning electron microscope images revealed densely packed crystalline compounds in the pores of the wastewater-treated slag. These compounds formed during the filtration process, strengthening the slag granules. Furthermore, both treated and raw slag chemically bonded better with cement compared to regular stone aggregates, creating a more cohesive microstructure.
The Green Dividend
Concrete made with the recycled slag aggregates achieved 32.5% higher 7-day strength and 8.2% higher 28-day strength compared to concrete made with untreated slag. The 28-day strength exceeded that of regular concrete by nearly 17%. The study shows how detailed knowledge of material chemistry can turn an industrial pollutant into a valuable resource, supporting the circular economy while making concrete production more sustainable.
Next Steps
While the initial results are promising, long-term durability studies are needed before this greener concrete can be used on a wider scale. Dr. Pramanik and colleagues are already planning these critical tests.
Research Team
Rajeev Roychand, Biplob Kumar Pramanik, Guomin Zhang, Sujeeva Setunge
Publication Reference
Recycling steel slag from municipal wastewater treatment plants into concrete applications – A step towards circular economy is published in the Journal of Resources, Conservation & Recycling (DOI: 10.1016/j.resconrec.2019.104533)
Picture Credit: RMIT University
From Lattes to Concrete: The Surprising Strength of Coffee Waste
Imagine sipping your morning latte and knowing that the spent coffee grounds from your cup could one day form the foundation of your home. This idea may soon become a reality, thanks to a groundbreaking study by engineers at RMIT University in Melbourne, Australia. They have discovered a way to create stronger concrete using roasted used coffee grounds, giving this popular beverage a second life as a building material while significantly reducing waste going to landfills.
Motivation Behind this Innovation
The driving force behind this groundbreaking study was the alarming amount of organic waste ending up in landfills, contributing significantly to greenhouse gas emissions. In Australia, approximately 6.87 million tonnes of organic waste are dumped in landfills annually, accounting for 3% of the country's total greenhouse gas emissions. Recognizing the urgent need to address this issue, the research team at RMIT University decided to shift their focus towards developing innovative solutions that could divert this waste from landfills and transform it into a valuable resource. Interestingly, the idea to start with coffee grounds emerged during a team meeting over a cup of coffee, highlighting the serendipitous nature of scientific discovery.
The Coffee Waste
Coffee is one of the most widely consumed beverages in the world, with millions of cups enjoyed daily. However, this popularity comes at a significant environmental cost. In Australia alone, around 75,000 tonnes of spent coffee grounds end up in landfills each year, contributing to a growing waste problem. Globally, this number skyrockets to a staggering 10 billion kilograms of coffee waste annually. As the world becomes increasingly focused on sustainability and waste reduction, researchers are constantly seeking innovative ways to repurpose these waste materials and mitigate their environmental impact.
From Coffee Waste to Biochar
Coffee is one of the most widely consumed beverages in the world, with millions of cups enjoyed daily. However, this popularity comes at a significant environmental cost. In Australia alone, around 75,000 tonnes of spent coffee grounds end up in landfills each year, contributing to a growing waste problem. Globally, this number skyrockets to a staggering 10 billion kilograms of coffee waste annually. As the world becomes increasingly focused on sustainability and waste reduction, researchers are constantly seeking innovative ways to repurpose these waste materials and mitigate their environmental impact.
Coffee Biochar for a Stronger Concrete
When incorporated into concrete, the coffee-derived biochar proved to have remarkable effects. At an optimal replacement level of 15% by volume of sand, the biochar increased the compressive strength of the concrete by an impressive 29.3%. The porous nature of the biochar allows it to absorb water and contribute to the internal curing of the concrete, leading to enhanced strength development.
The Role of Pyrolysis Temperature
The researchers found that the temperature at which the biochar is produced plays a crucial role in its effectiveness. Biochar created at 350°C provided the best results, while that produced at 500°C showed a decrease in strength due to its more fragile structure. This highlights the importance of fine-tuning the pyrolysis process to maximize the benefits of the biochar.
Environmental and Economic Benefits
- ~30% increase in concrete strength
- This significant increase in strength can be leveraged to reduce the required cement content
- Creates a potential for the 100% uptake of this waste material for concrete applications
- This waste to resource transformation creates a potential for diverting this waste from going to landfills, promoting sustainability, and closed loop circular economy.
Research Team
Rajeev Roychand, Shannon Kilmartin-Lynch, Mohammad Saberian, Jie Li, Guomin Zhang, Chun Qing Li
Publication Reference
Transforming spent coffee grounds into a valuable resource for the enhancement of concrete strength is published in the Journal of Cleaner Production (DOI: 10.1016/j.jclepro.2023.138205)
Picture Credit: Mohammad Islam, RMIT
Rubber Meets the Road: Transforming Tires into Sustainable Concrete
In a world where sustainability is no longer a choice but a necessity, engineers have achieved the remarkable feat of creating concrete that completely replaces conventional aggregates, such as gravel and crushed rock, with rubber derived from discarded tires.
A Pressing Issue
Every year, billions of waste tires end up in landfills, posing significant environmental challenges. These non-biodegradable materials not only occupy valuable land space but also contribute to air and water pollution when burned or stockpiled. The need for effective recycling methods has never been more urgent.
From Waste to Resource
Enter the visionary team of researchers from RMIT University in Melbourne, Australia. Led by Dr. Mohammad Momeen Ul Islam, they have developed an ingenious method that transforms waste tire rubber into a valuable resource for the construction industry.
Their innovative approach involves replacing conventional coarse aggregates in concrete entirely with rubber particles from end-of-life tires. By employing a novel compression casting technique, they have successfully created structural lightweight concrete with remarkable mechanical properties.
Strength and Sustainability
The rubber concrete developed by the RMIT team boasts a compressive strength of up to 97% higher than traditional rubberized concrete. This significant improvement in strength is achieved through the compression casting process, which minimizes the gaps between the rubber particles and the cement matrix, resulting in a denser and more durable material.
Moreover, the carbon footprint of this rubber concrete is substantially lower compared to conventional concrete. By utilizing waste tires, which would otherwise end up in landfills, the researchers have found a way to reduce the environmental impact of construction while also conserving natural resources.
A Greener Future
The potential applications of this rubber concrete are vast, ranging from residential construction to infrastructure projects. Its lightweight nature and impressive strength make it an attractive option for builders seeking sustainable alternatives to traditional concrete.
As the world grapples with the urgent need to combat climate change and reduce waste, innovations like rubber concrete offer a glimmer of hope. By turning waste into a valuable resource, we can pave the way to a greener, more sustainable future.
The research conducted by Dr. Islam, Dr. Li, and their team at RMIT University is a testament to the power of scientific ingenuity in addressing global challenges. As more industries embrace such eco-friendly solutions, we can look forward to a world where sustainability is not just a buzzword but a way of life.
Research Team
Mohammad Momeen Ul Islam, Jie Li, Yu-Fei Wu, Rajeev Roychand, Mohammad Saberian
Publication Reference
Design and strength optimization method for the production of structural lightweight concrete: An experimental investigation for the complete replacement of conventional coarse aggregates by waste rubber particles is published in the Journal of Resources, Conservation and Recycling (DOI: 10.1016/j.resconrec.2022.106390)
Picture Credit: RMIT University
Disposable PPE waste makes concrete stronger by up to 22%
Researchers at RMIT University have found a way to give new life to disposable personal protective equipment (PPE) waste by using it to strengthen concrete, offering a creative solution to the challenge of managing the surge of pandemic-related plastic waste. The RMIT team is the first to investigate the feasibility of recycling three key types of PPE – isolation gowns, face masks and rubber gloves – into concrete.
The environmental impact of PPE waste
The COVID-19 pandemic has not only strained healthcare systems worldwide but has also created a new stream of plastic waste in the form of discarded PPE. Globally, it is estimated that 129 billion face masks and 65 billion gloves are used each month. This surge in PPE waste has led to increased littering, with discarded items ending up in landfills and oceans, contributing to the growing problem of microplastic pollution.
Recycling PPE waste in concrete
To tackle this environmental challenge, the RMIT research team, led by Dr Shannon Kilmartin-Lynch, has investigated the potential of incorporating shredded PPE waste into structural concrete. By repurposing these materials, they aim to divert waste from landfills and reduce the environmental footprint of the construction industry.
- Nitrile gloves
- Polypropylene face masks
- Isolation gowns
Concrete Strengthening Mechanism
The researchers found that incorporating shredded PPE waste into concrete helps in improving its strength properties. The team attributed these improvements to the strong bond formed between the shredded PPE materials and the cement matrix, as observed through scanning electron microscopy. This strong bond allows for better stress transfer and crack bridging within the concrete mixture.
- Up to 22% higher strength with shredded nitrile gloves
- Up to 17% higher strength with shredded face masks
- Up to 15.5% higher strength with shredded Isolation gowns
Towards a circular economy
The research conducted by the RMIT team demonstrates the potential for a closed loop circular economy approach in the construction industry, where waste materials are repurposed as valuable resources. By incorporating PPE waste into concrete, not only can we reduce the environmental impact of the pandemic but also create a more sustainable built environment.
As the world continues to grapple with the challenges posed by COVID-19, it is crucial to find innovative solutions to manage the waste generated by the pandemic. The work of Dr. Li and his team at RMIT University serves as an inspiring example of how creative thinking and scientific research can help us build a more sustainable future.
Research Team
Shannon Kilmartin-Lynch, Rajeev Roychand, Mohammad Saberian, Jie Li, Guomin Zhang
Publication References
Application of COVID-19 single-use shredded nitrile gloves in structural concrete: Case study from Australia is published in the Journal of Science of The Total Environment (DOI: 10.1016/j.scitotenv.2021.151423)
Preliminary evaluation of the feasibility of using polypropylene fibres from COVID-19 single-use face masks to improve the mechanical properties of concrete is published in the Journal of Cleaner Production (DOI: 10.1016/j.jclepro.2021.126460)
A sustainable approach on the utilisation of COVID-19 plastic based isolation gowns in structural concrete is published in the Journal of Case Studies in Construction Materials (DOI: 10.1016/j.cscm.2022.e01408)
Picture Credit: RMIT University
High durability zero cement concrete beats corrosion and resists fatbergs
Researchers from RMIT University have pioneered an innovative zero cement concrete, wielding the power to eliminate corrosion and thwart the formation of fatbergs, thus extending the lifespan of infrastructure like never before.
The problem
Cement concrete, the backbone of our urban infrastructure, not only comes with high carbon footprint, but in the realm of sewage infrastructure, hides a dirty secret. The cement that binds the sand and gravel has a weak link i.e., free lime – a byproduct of cement hydration, that is released into the concrete. In the acidic sewage environment, the concrete rich in free lime becomes a vulnerable target to the corrosive acids, silently corroding the very core of sewage pipes. An even grimmer fate awaits on the inside of the pipes, where the same free lime reacts with fats, oils, and greases (FOGs) in the sewage to form giant, pipe-clogging "fatbergs". Maintaining and upgrading the sewage network comes with high costs and disruptions to the general public. With annual maintenance expenses reaching up to $15 million in Australia, tens of millions in the United Kingdom, and figure skyrocketing to billions in the USA, the financial burden on governments and taxpayers is undeniable.
Deciphering the Code
The team of researchers, led by Dr Rajeev Roychand, have cracked the code, unveiling how free lime, the hidden instigator of concrete corrosion, also plays a pivotal role in the formation of fatbergs. Furthermore, they have demonstrated how this innovative zero cement concrete, free from this inherent vulnerability, can play a crucial role in addressing these challenges.
The Innovation
By harnessing a cocktail of industrial byproducts like fly ash and slag, and fortifying it with nano-silica particles, the researchers have conjured up a concrete capable of withstanding the corrosive conditions inside sewers, while also help in preventing the sewers' worst enemies: corrosion and fatbergs. This innovation has the potential to revolutionize the way we build and maintain our infrastructure.
A sewer pipe dream come true?
While the researchers have shown it's possible to eliminate Portland cement from concrete sewage pipes, the long-term performance of this zero-cement concrete in real-world conditions still needs to be proven. Nevertheless, the study points the way to a future where concrete infrastructure is not only greener, but also lasts longer with less maintenance - a win for sustainability on multiple fronts.
Research Team
Rajeev Roychand, Jie Li, Saman De Silva, Mohammad Saberian, David Law, Biplob Kumar Pramanik
Publication Reference
Development of zero cement composite for the protection of concrete sewage pipes from corrosion and fatbergs is published in the Journal of Resources, Conservation & Recycling (DOI: 10.1016/j.resconrec.2020.105166)
Picture Credit: RMIT University
Double shot at circular economy - Steel slag soaks up toxins, then boosts concrete strength
Imagine a world where the by-products of steelmaking not only clean up wastewater but also contribute to creating stronger, more resilient concrete. Steel slag is a by-product generated during the production of steel and is porous in nature. It forms when impurities in the raw materials used to make steel, such as iron ore, coke, and limestone, are melted and separated from the molten steel.
The Innovation
An inter-disciplinary research team at RMIT, jointly led by Dr. Rajeev Roychand (Civil) and Dr. Biplob Kumar Pramanik (Environmental), have cracked the code, revealing the power of steel slag in a zero-waste strategy that not only benefits the environment but also boosts the circular economy. This innovative approach not only removes harmful chemicals from municipal wastewater but transforms the chemical and mineralogical composition of the slag, making it a star performer in enhancing concrete strength. It's a double win for sustainability—cleaner water and stronger structures, all from a by-product of steel manufacturing process!
Transformation of Slag Chemistry after Water Treatment
The most dramatic change was the massive increase in iron content after filtration. XRF showed that iron oxides shot up from a mere 0.7% in the original slag to a whopping 30.5% post-sewage treatment. This iron was present in new crystalline compounds like calcium aluminum iron oxide and wuestite, which were completely absent in the raw slag. Interestingly, common slag minerals like akermanite-gehlenite were no longer detectable after wastewater filtration, likely transforming into amorphous phases. The sewage-soaked slag also formed new phosphate-containing crystals, suggesting that some of the phosphorus removed from the wastewater was chemically incorporated into the slag.
The Microscopic Detective Work
Scanning electron microscope images revealed densely packed crystalline compounds in the pores of the wastewater-treated slag. These compounds formed during the filtration process, strengthening the slag granules. Furthermore, both treated and raw slag chemically bonded better with cement compared to regular stone aggregates, creating a more cohesive microstructure.
The Green Dividend
Concrete made with the recycled slag aggregates achieved 32.5% higher 7-day strength and 8.2% higher 28-day strength compared to concrete made with untreated slag. The 28-day strength exceeded that of regular concrete by nearly 17%. The study shows how detailed knowledge of material chemistry can turn an industrial pollutant into a valuable resource, supporting the circular economy while making concrete production more sustainable.
Next Steps
While the initial results are promising, long-term durability studies are needed before this greener concrete can be used on a wider scale. Dr. Pramanik and colleagues are already planning these critical tests.
Research Team
Rajeev Roychand, Biplob Kumar Pramanik, Guomin Zhang, Sujeeva Setunge
Publication Reference
Recycling steel slag from municipal wastewater treatment plants into concrete applications – A step towards circular economy is published in the Journal of Resources, Conservation & Recycling (DOI: 10.1016/j.resconrec.2019.104533)
