Outside the box.. Cement recycling in steel furnaces

Out of the box.. Cement recycling in steel furnaces

Researchers at the University of Cambridge have developed a new, ultra-low-emissions method for producing concrete, an innovation that could transform the building materials industry. In order to reach net zero emissions. The new method - which the researchers describe as a “true miracle” - uses electric arc furnaces (EAF), which are used to recycle steel. To recycle cement at the same time. Cement - as we know - is the component with the largest carbon footprint in the concrete mixture.

Concrete is considered the second most used material - after water - on this planet, and it is responsible for about 7.5% of the total carbon dioxide emissions resulting from human activities, which has prompted the scientific and industrial community to research and develop to find green solutions that can reduce the carbon footprint of this material that forms the backbone of development and construction in our contemporary world.

Outside the box idea

Electric arc furnaces are furnaces that use electric current to reach the temperatures needed to recycle steel. This process includes the use of what is known as “magma,” which helps increase the metal’s ability to melt and flow. It also collects impurities on the surface of the melt in a layer known as slag, so that this layer protects the melt from the air. To prevent it from being oxidized.

In this context, Cambridge researchers found that cement found in spent concrete - such as demolition and construction waste - could represent a suitable alternative to lime, which is used as a lime flux in steel recycling. The idea is to grind the concrete waste so finely that the cement can be separated from the sand and gravel. After that, this cement can be used as a magmatic material instead of lime. The resulting slag isrecycled portland cement, which can be used again to produce new concrete.

What is special about the cement recycling method, developed by Cambridge researchers and published by Nature magazine; It does not require adding any new investments in concrete or steel factories in order to adopt this technology, as it can rely on existing production lines, and it also significantly reduces emissions resulting from the production of both concrete and steel. Due to the reduced need to use virgin cement, or add lime.

Recent tests conducted by the Institute of Materials Processing, located in the north of England, and a partner in this research project, have shown that recycled cement can be produced on a large scale in an electric arc furnace (EAF), which is the first time this has been achieved. This method may also enable us in the future to produce emissions-free cement, but on the condition that the referred electric arc furnaces are operated with renewable energy.

Professor Julian Allwood from the Department of Engineering at Cambridge, who led the research, said: “We held a series of workshops with leading companies working in the building materials industry on how to reduce emissions resulting from this sector. The result of these discussions was that we came up with many great ideas, but the question that everyone overlooked is: How can we transform the future of the world to be free of cement?

The problem in cement production

Concrete - as we know - is produced by mixing sand with gravel, water and cement, where the latter acts as the binding material for all the components. Although the percentage of cement in concrete is considered small, it is responsible for approximately 90% of concrete mixture emissions.

Cement is manufactured through a process that includes many stages, where limestone and a group of other raw materials are crushed and ground. After this, these materials are heated at about 1450 degrees Celsius in large rotating kilns, to produce what is known as “clinker,” which is then ground with gypsum and other additives in varying proportions. To obtain the final product: cement.

The problem in the cement industry lies in the stages of heating and burning the raw materials. In addition to consuming huge amounts of coal and other types of fossil fuels, which in turn release huge amounts of Greenhouse Gases (GHGs) - the process also produces large amounts of carbon dioxide. As a result of converting limestone (CaCO3) into lime (CaO) by heat.

Given the large carbon footprint and huge energy consumption, scientists and researchers have worked throughout the past decade on studying various alternatives to cement, and they found that approximately half of the amount of cement present in concrete can be replaced with alternative materials, such as fly ash (ash), but these alternatives need to be activated - chemically - by cement. So you can harden.

Allwood said: “The only problem is not finding alternatives to cement. The scientific community has already been able to find alternatives. But the other problem here is our inability to provide these alternatives in the appropriate quantity, so as to meet the increasing global demand for cement, which has exceeded the barrier of 4 billion tons annually. Therefore, achieving zero emissions in this industry requires thinking outside the box.”

Rapid and promising development

The clinker production process - as we mentioned - requires heat and specific percentages of oxides, and when looking at spent cement we find that it contains the same percentages of these oxides, except that it needs reactivation. So it can be used again.

From this standpoint, the researchers tested a variety of furnace slag resulting from the use of demolition waste as a magma material in the electric arc furnace, with the addition of lime, alumina, and silica. The slag is then processed in the electric furnace, along with the molten steel, before it is quickly cooled - air-cooled.

Researchers found that a mixture of cement clinker and iron oxide is an excellent slag for steelmaking. Because it is foamy, it can flow well, and - with the use of the correct proportions and rapid cooling of this slag - we can reactivate cement, and all this without requiring any additional investments or radical modifications in the steelmaking process.

Cement resulting from this recycling process contains higher levels of iron oxide than conventional cement, but researchers say this will have a minimal impact on performance and safety.

It is worth noting that the innovative method of Cambridge researchers in producing cement in steel electric arc furnaces; It is developing rapidly, as it has already moved from laboratory application to experimental application on an industrial level. This is what made researchers believe that this method could be responsible for producing one billion tons - annually - of cement by the year 2050, which represents about a quarter of cement production - annually - at the present time.

Alwood said: “Producing cement without emissions is a dream that haunts the scientific and industrial community alike, but in the same context, we must also reduce dependence on the cement and concrete that we use. Although concrete is cheap and strong, it can be manufactured almost anywhere; Increasing reliance on them could make the world reluctant to find more environmentally friendly solutions. Therefore, there must be a societal and political will to limit the use of cement and concrete, and find appropriate alternatives to them.”

Multi-pronged approach

What interested us at Earth Guards about this promising study is that it follows an approach that achieves many goals at the same time. On the one hand, the innovative method of recycling cement can provide an environmentally friendly solution and reduce our need to produce virgin cement, which in turn will lead to a significant reduction in carbon emissions that contributes to reducing climate change, and consequently achieving a number of Sustainable Development Goals (SDGs).

On the other hand, this green approach can represent a real solution to demolition and construction waste, which represents millions of tons annually, and unfortunately, this waste is often disposed of in an unorganized manner. Therefore, by converting this waste into a raw material again, we will be able to control the circulation of this waste, and integrate it into the circular economy.

Achieving the Sustainable Development Goals (SDGs) requires all of us to think outside the box. To find innovative solutions that can transform the major problems we face today into sustainable alternatives, something that Protectors of the Earth seeks to support with all force, by highlighting the most prominent research and creative solutions around the world. Believing in the pivotal role of spreading awareness and sustainable culture in creating a bright future for our coming generations.