The strength, durability, recyclability and economy of structural steel make it a highly valuable building material that has been used to create many prominent buildings and structures worldwide.
It’s well known that the production of steel consumes immense amounts of energy and generates large quantities of pollution. According to the AIA’s Sustainable Design Resource Guide (1997), the global steel industry is responsible for the production of approximately 5% of all greenhouse gases.
On the plus side, steel is fully recyclable and is the most recycled material in the world, with an average rate of over 60%. Recycling steel is environmentally and economically beneficial since fabricating steel from scrap requires one quarter of the energy needed to produce it from virgin materials. Preferable to recycling is the reuse of a building’s steel components. However, many practical and economic difficulties with steel reuse must be overcome before it can become a common practice.
While steel’s benefits will ensure it remains an integral part of modern design and construction, it is important for architects and engineers to be conscious of the environmental impacts associated with its production and use. The manner in which structural steel is produced and used has a key role to play in efforts toward sustainability.
The two primary methods of steel production employed today are the Basic Oxygen Furnace (BOF) and the Electric Arc Furnace (EAF) processes. Both processes rely on recycled steel content to decrease manufacturing costs.
EAFs are the most efficient furnaces and account for about 45% of steel production in North America. Despite this, an EAF consumes enough energy to supply power to a town of 100,000 residents. EAFs are powered by coal-fired power plants that produce very high greenhouse gas emissions and deplete non-renewable fossil fuels. The advantage is that EAFs operate on virtually 100% scrap, while a BOF typically uses 15-30% scrap. Generally, the average amount of recycled content in structural steel is approximately 66%.
The steel industry has seen dramatic improvements in emissions control and efficiency over the past 30 years. But despite these advances, steel manufacturing remains a highly energy-intensive activity, and a significant source of pollution. Although steel typically comprises only 23% of building materials by weight, steel production accounts for 48% of the total energy used to manufacture those materials.
Steel can be recycled “infinitely” without suffering from degradation or the loss of inherent material properties. Steel manufacturers have been practicing recycling for most of the industry’s 150-year history, partly because incorporating scrap steel into the manufacturing process lowers the cost of production. This has created an extensive infrastructure for scrap collection, processing and distribution.
Steel recycling also reduces the demand for virgin materials. For every tonne of steel that is recycled, 1,140 kg of iron ore, 450 kg of coal, and 20 kg of limestone are saved. Reducing the need for these materials prevents habitat loss and pollution due to production. Finally, producing steel from scrap results in about one quarter the greenhouse gas emissions required for steel produced using virgin materials.
Despite the benefits, achieving true sustainability in steel production or the production of any other building material seems unlikely. Even if the steel industry achieved a near-100% recycling rate, the delay between steel’s initial manufacture and recovery–which could be 50-100 years for many buildings–and the ever-increasing demand for steel will require extraction and depletion of raw materials to continue.
Reuse of Steel Elements
The reuse of structural steel elements from buildings is highly desirable since energy is only required for deconstruction and transportation. Currently, economic and practical issues make reuse a less appealing alternative to recycling.
Once out of service, most structures are demolished and their components become unsalvageable. Even when the time is taken to remove intact steel elements, the material properties must be confirmed and the extent of deterioration evaluated. While the steel recycling sector has a well-established infrastructure, there is no equivalent for steel reuse.
There is growing interest in the careful deconstruction of buildings, so that components can be fully and individually salvaged for either recycling or reuse. It has been suggested that deconstruction could be more practical if buildings were designed at the outset with future disassembly in mind. As the prices of energy and materials increase, and as disposal space becomes scarce, disassembling buildings and salvaging their components may soon become more cost-effective.
Conscious Use of Steel
Design decisions by architects and engineers can help decrease the impact of steel production on our environment. The development of new high-performance steel and increasingly more accurate ways of analyzing steel properties are allowing professionals to arrive at more efficient designs and reduce resource use.
As steel reuse becomes more economical, design professionals must begin to consider the future deconstruction of buildings as carefully as they consider their construction. This will allow structural components to be reused, and will help minimize the amount of building waste sent to landfill.
Structural steel is a building material that has allowed engineers and architects of the 19th and 20th centuries to achieve remarkable feats of design and construction. While steel continues to be of the utmost importance to modern industrial economies, we must remember that it comes at a relatively high environmental price. Efficient and conscientious design can help reduce waste, encourage recycling and enable the reuse of structural steel while ensuring it is produced and used in a sustainable manner.
Brennan Vollering, M.A.Sc., P. Eng. is Project Engineer and Thorsten Klaus is a student intern at Halsall Associates Limited, a leading Canadian structural engineering and building sciences firm. Visit the Halsall Web site at www.halsall.com.