An essential building material

Starting from the earliest beginnings of human civilisation, we can easily see how concrete structures have always been a key component of modern civilisation. In fact, concrete is used for building bridges and roads, and concrete is the most consumed material on Earth, while the steel used to reinforce it is the most used metal. Of course, this is not without its downsides, the main one being the high environmental impact: concrete is, in fact, responsible for 8% of global CO2 emissions. Nowadays, cement and concrete are among the most consumed materials worldwide. About 4.1 billion tons of cement are produced each year, half of which is produced by China alone. Although the cement and concrete industries strive to reduce the devastating effects on the environment through continuous improvement of production techniques and product standards, current measures alone are insufficient to deal with the environmental and waste disposal problem. Since it is neither possible to stop concrete production nor to replace it in the short term, the direction that has been taken is to try to reduce the environmental effects of the material but without compromising its performance. Recent research suggests that a solution may be found in recycled industrial waste, in particular, a by-product called steel slag. 

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No-Fines Concrete with Steel Slag Samples_[Photograph]_©Korat, L. (2015)
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Steel slag aggregate_[Photograph]_©Steel Slag Association

A breakthrough material for architecture

Steel slag is a by-product resulting from the oxidation of impurities in pig iron during the steelmaking process. Different types of steel slag are obtained depending on the production method used, each serving a different purpose. Using steel slag as fine aggregate also brings with it many advantages in terms of compressive strength. Steel slag, although in the past it could pose a severe threat to the environment due to its release into nature, is currently used in various fields as fine and coarse aggregates for concrete. Using steel slag in all these applications provides an optimal solution for resolving environmental problems caused by waste. Of all waste materials, it is one of the most encouraging from the point of view of its structural capacity. Due to its high mechanical strength, porosity, and water absorption, steel slag is already being used as a fine and coarse aggregate in many different areas. Its use in concrete is increasingly recognised for its environmental and physical properties, indicating that it could be a suitable material for high-strength concrete structures or for any other structure that could take advantage of its increased durability and sustainability. Australian scientists made a new type of concrete with steel slag, and the remarkable discovery was that the results were 17% better. 

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Carbon-neutral concrete_[Photograph]_©Sandberg, H. (2022)

New borders for sustainability

“The global steel industry produces more than 130 million tons of steel slag each year,” explains water engineer Biplob Pramanik of RMIT University in Melbourne. Through data shared by the World Steel Association, about 15.7 million tons of steel slag is produced in Europe alone, and of that, just 11.5 million tons are recycled. This huge amount of slag produced worldwide is by itself a major motivation for recycling the material, which would otherwise be wasted. Numbers that make the slag produced abundantly and also potentially valuable. Using steel slag in concrete reduces the amount of waste generated by the steel industry. In fact, given the high contamination caused by industrial waste, giving it new value is a great way to contribute to the circular economy. At the same time, concrete with steel slag also offers an additional benefit: it reduces the need for virgin aggregate materials, reducing CO2 emissions while maintaining the excellent physical qualities of concrete. Another key reason steel slag concrete has been considered a viable substitute for traditional concrete is that it offers many benefits beyond environmental sustainability. When the concrete is placed and weathered, the steel slag acts as a filler and thus helps to improve the density of the concrete, which in turn improves its strength and durability.

Wind Tower_[Photograph]_(Salmiya: Kuwait)_©Agi Architects (2017)

Benefits and disadvantages

However, this new type of material also has disadvantages. Those are, for example, the transportation costs, which are about 20% more expensive than traditional natural aggregates due to their high specific gravity. Despite that, steel slag can work as supplementary cementitious materials and fine and coarse aggregates in sustainable cement and concrete industries. This shows that the steel, cement, and concrete industries form a perfect industrial ecological relationship with each other for sustainable development in developed and developing countries. In addition, the use of industrial by-products such as steel slag largely reduces evening gas emissions and energy consumption without compromising the mechanical, physical, and durability properties of concrete. It is clear from analyses and studies that Portland cement cannot be 100% replaced with additional cementitious materials, but the amount of Portland cement can be reduced mainly through mixing with ground steel slag. The use of this material as aggregate in concrete could provide an economical and environmentally friendly solution. As the demand for aggregates is increasing (as is the demand for concrete), finding suitable alternatives for the future is becoming increasingly important.


Valeria Montjoy (2023) What is Steel Slag Concrete? [Online] Accessible at: [Accessed date: 2023/02/02]

Osman Gencel, Omer Karadag, Osman Hulusi Oren, Turhan Bilir (2021) Steel slag and its applications in cement and concrete technology: A review, Construction and Building Materials [Online] Accessible at: Steel slag and its applications in cement and concrete technology: A review – ScienceDirect  [Accessed date: 2023/02/02]

Subathra Devi, B.K. Gnanavel (2014) Properties of Concrete Manufactured Using Steel Slag [Online] Accessible at: Properties of Concrete Manufactured Using Steel Slag – ScienceDirect [Accessed date: 2023/02/02]


Laura Salurso is an architecture and design graduate with a strong passion for traveling, writing and photography. She has always looked at things around her from an architectural point of view, observing and studying the strong and archetypical connection between architecture and people.