By Nidhi DhullReviewed by Susha Cheriyedath, M.Sc.Aug 15 2024Steel is a top choice for sustainable construction due to its 100 % recyclability, retaining its physical and chemical properties throughout the process.
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Steel products and by-products can be readily recycled into new constructions, reducing the need for raw materials and conserving resources.1,2 As a result, utilizing recycled steel helps to lessen the environmental impact of the construction industry and decrease carbon emissions associated with steel production.3
Both iron ore and scrap-based steelmaking generate several by-products, including slags, dusts, mill scales, and sludges, with slag being the most significant. Steel slag, rich in valuable elements like iron, is particularly beneficial for recycling and finds use in applications such as cement production, road construction, and marine environment restoration.2
This article explores the various ways recycled steel and steelmaking by-products can be utilized as sustainable construction materials.
Recycled Steel as Construction Materials
Primary steel is produced from iron using either a basic oxygen furnace or an electric arc furnace, with these processes emitting approximately 1000-2500 kg of CO2 equivalent per ton of steel. To address the increasing resource demands for primary steelmaking and construction projects, scrap steel generated during steelmaking can be captured and recycled.3
Carbon steel slag, a by-product of low-carbon steel production in electric arc furnaces, often ends up in landfills, posing environmental hazards. However, this slag is highly beneficial for constructing roads, pavements, and other infrastructure, which helps reduce landfill use and conserve non-renewable resources. Steel slag aggregates can also replace high-quality silicate aggregates in concrete and mortar.1
Other by-products of steelmaking, such as dust and sludges, contain significant amounts of iron oxides and carbon and can be recycled for use in Portland cement. Additionally, mill scales, produced during the casting and rolling stages under oxidizing conditions, can be processed into briquettes and pellets for use as biomass fuels in brick manufacturing.2
Recycling and reusing steel components from demolished structures necessitate a thorough assessment of their structural integrity, involving designers, constructors, and building owners. Once evaluated, recycled steel can be repurposed into new structures or structural elements, thereby supporting sustainable construction practices.
Applications and Advantages
Using recycled steel in new construction projects has a host of benefits. For starters, it helps reduce waste by keeping materials out of landfills and supports sustainability through a circular economy. Plus, recycling steel is much more energy-efficient than the traditional steelmaking process, which significantly reduces the industry's carbon footprint.1
Recycled steel and steel slag can be turned into highly valuable construction materials. Steel slag, for example, is often used to replace cement in concrete, offering both environmental and cost-saving benefits. Its unique properties also make it a great choice for use in embankments, road construction, dams, asphalt pavements, concrete masonry, and soil improvement.1,2 In road construction, slag can even outperform natural aggregates in terms of mechanical properties.1
Steel slag is similar to artificial rock aggregates, providing high strength, great weathering resistance, and excellent durability. It is versatile enough to be used in making cement, bricks, concrete, wall materials, and ceramic tiles, which helps cut down the need for natural raw materials. Additionally, the high porosity and large surface area of steel slag make it perfect for restoring coral reefs and building artificial reefs in marine environments. It can also be used to absorb harmful substances like hydrogen sulfide (H2S) and metalloid contaminants.2
Flue dust from the steelmaking process contains considerable amounts of iron oxides and coke fines. Consequently, it can be recycled as fuel or raw material for cement production.1
Structures built with recycled steel are not only durable and resilient but also have the advantage of being repurposed once their original life is over. This approach supports a closed-loop system that minimizes waste and maximizes efficiency. In essence, using recycled steel in construction is a smart choice that balances environmental responsibility, economic benefits, and efficient use of resources, all while promoting sustainability.1
Challenges
While using recycled steel and slag in construction offers significant benefits, it also presents several challenges. One major issue is economic: sourcing recycled materials can be more costly and resource-intensive compared to using new materials. This is partly because procuring and processing recycled components often involves additional efforts that drive up costs.1
Natural materials are typically less expensive than recycled ones, and recycling can sometimes be more costly than simply disposing of waste. Recovering reusable elements from existing structures through deconstruction is also more complex and time-consuming than straightforward demolition. Additionally, the lack of standardized design rules for recycled materials can lead to increased costs and inefficiencies, making recycled steel less economically viable in some projects.1,3
Moreover, recycled steel and slag do not always improve the properties of constructed structures. For example, slag can cause volumetric expansion when used in road construction, which is a significant concern. These properties need to be carefully evaluated based on the temperature and humidity conditions at the construction site.
The construction and waste disposal industries are well-established, with substantial investments in equipment and processes designed for efficient handling. In contrast, recycling involves multiple stages—recovery, sorting, reprocessing, and repurposing—which add to the overall cost of recycled materials and construction projects.3
Recent Developments and Future Prospects
Recycled steel is increasingly being explored for its potential in sustainable construction. For example, a recent study published in Construction and Building Materials highlighted the use of recycled steel slag in radiation-shielding concrete. The research found that adding steel slag to concrete improves its ability to shield against gamma and neutron radiation. This slag-enriched concrete not only enhances compressive and tensile strength but also offers higher linear attenuation, a larger removal cross-section, and a reduced half-value layer compared to traditional concrete.4
Another study in Materials investigated the use of recycled steel fibers to control plastic shrinkage cracks in concrete. Recycled steel fibers derived from old tires were found to be more effective in minimizing plastic shrinkage and micro-cracks compared to new, manufactured fibers. These recycled fibers can also prevent crack development and propagation, even in extreme environmental conditions.5
The potential for recycled steel in construction is promising and likely to grow as the sector continues to focus on sustainability. However, achieving this potential requires advancements in technology and material science to improve the quality, durability, and cost-effectiveness of recycled steel, making it more competitive for infrastructure projects.
To accelerate the adoption of recycled steel, several factors are crucial: non-destructive testing methods, remote and drone surveys, better supply chain integration, standardized design practices, and fiscal incentives. These elements can help streamline the recycling process, enhance material performance, and make recycled steel a more attractive option in the evolving landscape of sustainable construction.
References and Further Reading
1. Puma, G. C. C., Salles, A., Turk, J., Ungureanu, V., & Bragança, L. (2024). Utilisation of Reused Steel and Slag: Analysing the Circular Economy Benefits through Three Case Studies. Buildings, 14(4), 979. DOI: 10.3390/buildings14040979, https://www.mdpi.com/2075-5309/14/4/979
2. Branca, T. A. et al. (2020). Reuse and Recycling of By-Products in the Steel Sector: Recent Achievements Paving the Way to Circular Economy and Industrial Symbiosis in Europe. Metals, 10(3), 345. DOI: 10.3390/met10030345, https://www.mdpi.com/2075-4701/10/3/345
3. Kanyilmaz, A., Birhane, M., Fishwick, R., & Castillo, C. (2023). Reuse of Steel in the Construction Industry: Challenges and Opportunities. International Journal of Steel Structures. DOI: 10.1007/s13296-023-00778-4,
https://link.springer.com/article/10.1007/s13296-023-00778-4
4. Aliyah, F., Kambali, I., Setiawan, A. F., Radzi, Y. M., & Rahman, A. A. (2023). Utilization of steel slag from industrial waste for ionizing radiation shielding concrete: A systematic review. Construction and Building Materials, 382, 131360. DOI: 10.1016/j.conbuildmat.2023.131360, https://www.sciencedirect.com/science/article/abs/pii/S0950061823010735
5. Alshammari, T. O., Pilakoutas, K., & Guadagnini, M. (2023). Performance of Manufactured and Recycled Steel Fibres in Restraining Concrete Plastic Shrinkage Cracks. Materials, 16(2), 713. DOI: 10.3390/ma16020713, https://www.mdpi.com/1996-1944/16/2/713
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