Carbon Impacts of Steel
Steel is manufactured in two types of factories. Large steel mills typically use basic oxygen furnaces (BOFs), which burns coal or natural gas to melt iron-ore to extract the iron, and then mixes the iron with scraps of iron and steel to make new steel. Most of the inputs to a BOF are mined, raw materials, so the recycled content level for BOFs is typically between 25%-37%. Recycled content is important because virgin steel can have an embodied carbon footprint that is up to five times greater than high-recycled content steel1.
Smaller factories normally use electric arc furnaces (EAFs) to melt scrap iron and steel into new steel. These factories don’t have the ability to process raw iron ore. As a result, the steel manufactured on EAFs has high levels of recycled content, up to 100%, with an average recycled content of 93% for hot rolled shapes2. Structural steel does not lose any of its metallurgical properties (the physical and chemical behavior of the alloys) when is is recycled, making the properties and performance characteristics of recycled steel equivalent to virgin steel3. EAFs are powered by electricity, rather than coal and natural gas, and therefore have the ability to be powered using renewable energy sources.
Using steel from electric arc furnaces is the best way to reduce embodied emissions in steel, because EAFs uses high levels of recycled material and can be powered by renewable energy sources.
Carbon Smart Attributes
Use steel that comes from electric arc furnaces (EAFs)
EAFs produce less than half as much CO2 as basic oxygen furnaces (BOFs)4, and even less when the source energy is renewable energy. Use structural steel that come from EAFs instead of steel from BOFs whenever possible. See Design Guidance for more information.
Use recycled steel
Virgin steel can have an embodied carbon footprint that is up to five times greater than high-recycled content steel1. EAFs use an average of 93% recycled content, where BOFs use an average of 25% recycled content. Use high-recycled content steel whenever possible.
Design & Construction Guidance
Use shapes that come from electric arc furnaces
North American manufacturers typically use electric arc furnaces to manufacture steel for hot rolled shapes like wide-flange members, angles, channel shapes, and rebar. Hollow structural shapes (HSS) and metal deck require a second process to roll the steel into its form, and tend to come from BOF mills that use less recycled content. Plates can be produced on either an EAF or BOF mill.
Utilize salvaged or reclaimed structural steel
There are used pipe dealers that offer pipe from decommissioned from oil and gas facilities and distribution systems. Use these pipes for pipe piles or columns, where possible, to eliminate the emissions associated with creating new materials5.
Use braced frames instead of moment-resisting frames
For the building’s lateral-load-resisting system, a recent study found that using braced frames instead of moment frames in a 3-story building reduced the embodied carbon impact of the building structure by 12%6,7. This is because moment-resisting frames and beams tend to be significantly heavier and require more material than braced frames in order to transfer forces and resist lateral loads. Additionally, a greater number of moment-resisting frames are often needed, compared to braced frames, to support the same load8.
Use joists or trussed members instead of rolled shapes
Joists and trussed members are often lighter and can support the same weight compared to heavier rolled shapes. Using joists and trussed members may reduce the overall quantity of steel required thus reducing the embodied carbon impact of the structure (for example, see resources).
Rightsize: one size does not fit all
Right-sizing steel members reduces excess material and thus reduces the embodied carbon impact of a project. Plan ahead and size each member precisely, instead of using set sizes for the whole project.
Utilize higher grade steel
Use higher grade steel, which can accomplish the same structural task using less material. However, ensure that the increased strength of the material does not result in additional CO2 emissions.
Design for adaptability and deconstruction
Due to its metal fasteners and standardization, structural steel framing is well suited for deconstruction and reuse. Make a plan to have structural steel members recycled or reused at the end of the building’s life.
Use reinforcement only when needed
Some applications of concrete (e.g. some slabs on grade) can be used without steel reinforcement as long as alternate crack control measures are taken. Whenever possible eliminate steel reinforcement from concrete to reduce the project’s overall embodied carbon footprint.
Work with fabricators to increase the efficiency of your design
Work with steel fabricators, explaining your objective for low carbon emissions by reducing steel quantities, using higher grade steel, and/or increasing the use of recycled steel(4).
Contact steel producers directly
Designers should contact producers directly to inquire about the specific production methods used to produce the structural steel for their project.
1 | 10 Steps to Reducing Embodied Carbon, Larry Strain
2 | More than Recycled Content: The Sustainable Characteristics of Structural Steel, AISC 2017
3 | Recycled Content in Steel, Building Green 2009
4 | ASCE/SEI Sustainability Guidelines for the Structural Engineer (See Steel chapter)
5 | Case study: NREL, Colorado. “Recycled Natural Gas Pipes Shore Up Green Building”
6 | ASCE/SEI Structural Materials and Global Climate (See Steel chapter)
7 | Nadoushani et al. 2015, “Effects of Structural System on the Life cycle Carbon Footprint of Buildings”
8 | Civil+Structural Engineer: Steel Moment Frames 101, 2014
SRI (Steel Recycling Institute). (2013). Cradle-to-gate Life Cycle Inventory (LCI) data for steel products, Pittsburgh, PA.
Effects of Structural System on the Life cycle Carbon Footprint of Buildings, Nadoushani et. al