Steel and Impacts on the Environment

According to the U.S. EPA, “Gases with a higher GWP [global warming potential] absorb more energy, per pound, than gases with a lower GWP, and thus contribute more to warming Earth.” The people at the SMDI want you to know that over its entire lifecycle, steel has a lot less GWP than aluminum. 

Mark Thimons is talking about building buildings with wood. Not just framing houses. But the work done by StructureCraft (structurecraft.com) in Minneapolis, the construction of the T3, a seven-story office building in downtown Minneapolis. The mixed-use building, designed by Michael Green Architecture and DLR Group, with MKA, has a concrete level at the bottom, but six stories of wood structure above it, materials like Nail-Laminated Timer panels.

StructureCraft built the 180,000-ft2 superstructure for the building in 9.5 weeks. Thimons, who is a registered professional engineer in Pennsylvania and a LEED-accredited professional in building design and construction (that’s as in the Leadership in Energy and Environmental Design green building rating system established by the U.S. Green Building Council), knows a little something about environmentally-based design practices.

But what Thimons is talking about isn’t wood. It’s steel. More specifically, about the greenhouse gas (GHG) emissions that are associated with materials during their lifecycle—as in from processing to recycling with use sandwiched in the middle.

Thimons also happens to be the vice president, Sustainability, Steel Market Development Institute (SMDI; smdisteel.org), a business unit of the American Iron and Steel Institute (AISI), where he is responsible for overseeing the Steel Recycling Institute and research projects in an array of markets, including construction. And automotive.

He makes the point that many architects are becoming tuned in to designing with materials’ environmental impacts (in addition to things like strength, durability and fire performance).

Here’s something that you probably didn’t realize: according to the AISI, a steel utility pole, compared to the trees stripped of bark and branches that you commonly see punctuating the landscape, is 30 percent lighter. This means that the steel pole is less costly to transport.

But Thimons’ real focus is not going toe-to-toe with wood. Rather, it is what has become the bête noire for steel in automotive: Aluminum.

“It’s a big deal.”
In November 2017, the Steel Recycling Institute released a peer-reviewed study titled “Life Cycle Greenhouse Gas and Energy Study of Automotive Lightweighting.”

The purpose: “The intent of the study is to develop comparative claims and assess trade-offs associated with automotive lightweighting by material substitution on the basis of life cycle GWP-100 [100-year global warming potential] and energy consumption.” 

There are footnotes and tables and figures. There is nearly impenetrable prose (for those who are not necessarily in the know vis-à-vis such things as Material Replacement Coefficients and Monte Carlo simulations). The study employs a peer-reviewed vehicle life cycle model developed by Dr. Roland Geyer at the University of California Santa Barbara.

Dr. Jody Hall, vice president, Automotive Market, SMDI, says that they’d released a white paper showing these findings two years ago, but because they realized that people might simply think, “Of course the steel industry is going to claim the superiority of steel over aluminum,” they decided to get the material vetted such that it would have solid credibility, which took the additional time.

“It is a big deal to us,” she says.

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Breaking it down.
So let’s simplify things.

The premise is that while federal regulations are focused on fuel economy and the consequent emissions from the combustion, what they call the “vehicle use phase,” they maintain “the complete GHG and energy profile of a vehicle is only evident by considering the entire life cycle.”

They looked at an array of model year vehicle types accounting for some 70 percent of all vehicles produced in North America. These vehicles are:
  • Compact battery electric: Nissan LEAF
  • Midsize: Chevrolet Malibu, Ford Fusion, Honda Accord, Hyundai Sonata, Nissan Altima, Toyota Camry
  • SUV: Chevrolet Equinox, Ford Escape, Honda CR-V, Nissan Rogue, Toyota RAV4, Ford Explorer, Jeep Grand Cherokee
  • Truck: Chevrolet Silverado, Ford F-Series, Ram 
  • Midsize hybrid: Chevrolet Volt, Ford Fusion SE Hybrid, Camry Hybrid LE, Prius

Then they developed a weighted average, an index of materials used, and then looked at one variant that is substantially produced with advanced high strength steel (AHSS) and one that is aluminum-intensive. They considered secondary mass savings (e.g., lighter primary structure means lighter brakes).

For the pickups, they set the lifetime driving range at 180,000 miles. It was set at 160,000 for the rest of the vehicles.

As for the life cycle: “The vehicle life cycle processes within the system boundary include raw material extraction and processing, the production and finishing of auto part materials (including casting, extrusion, rolling, and galvanizing), part manufacturing (including plastic molding processes and prompt scrap generation during part stamping/forming processes, but excluding stamping energy), vehicle assembly, fuel and fluids production and consumption during vehicle use, and recycling of materials at end-of-life.”

What it says.
There are several conclusions drawn. To cherry pick what seems to be the most pertinent (and clear):
  • “The use of aluminum instead of AHSS to lightweight the body structure and closures of the vehicles in this study resulted in a significant increase in production of GHG emissions and energy consumption for every scenario. These emissions occur at the start of (and continue to impact the atmosphere throughout) the vehicle life cycle.
  • “The increase in production emissions for vehicles lightweighted with aluminum vs. AHSS is not offset by emission reduction benefits during the use phase until at least the end of the vehicle’s useful lifetime, if at all, and only when the avoided burden recycling methodology is used to model steel and aluminum scrap recycling.
  • “[F]uel economy regulations for U.S. vehicles have been established to improve vehicle fuel economy and reduce GHG emissions. This study demonstrates, however, that concentrating exclusively on use phase (driving) emissions does not achieve an overall reduction in emissions with any degree of certainty. This is because increased production emissions have been shown in a variety of cases to outweigh emission reductions in the use phase, resulting in a net increase in emissions to the atmosphere.”

To synthesize those points, what it comes down to is that it takes a lot of energy to create aluminum (Hall: “It takes seven times the amount of energy to covert the ore to make aluminum than the ore to make steel. That’s just basic physics.”), so even though the vehicle made with aluminum may be lighter than a comparable one made of AHSS, the reduced GHG emissions of the lighter car will not offset the amount of GHG emissions generated during the production phase of the life cycle. 

Then there is the issue of how the recycling of the material is accounted for as regards emissions (there are three methods, the avoided burden method in the second point, as well as the 50/50 method and the recycled content method). About this aspect, Thimons says, “In this study, we were very generous to aluminum in the assumptions we made about end-of-life recycling.” But he adds, “There is a question about how much end-of-life automotive aluminum actually makes its way back to sheet products used in other aluminum components for vehicles,” and says, “One of the real advantages of steel is that it can be recycled from one product into another.”

Still, when you get to the third bullet above, there is the simple fact that federal regulations right now are not looking at the life cycle. And chances are, for the next few years it is unlikely that regulators will look at the life cycle, and that even the use phase requirements are likely to be eased. In the U.S.

Hall: “Automakers have to meet emissions requirement globally. Most of the automakers’ platforms are global.”

So while changes in U.S. CAFE change things in the U.S., selling vehicles in much of the rest of the world necessitates improvements in such things as powertrain efficiency, aerodynamics, reduced rolling resistance and vehicle mass.

Will it tip?
Which brings us back to the construction industry that we started with. Thimons says, “Nobody has ever suggested that greenhouse gas emissions are the primary reason why one person selects a material over another.” There are other factors to consider, from fundamental performance requirements to cost. Which are many of the same considerations when it comes to selecting materials for automotive use.

But Thimons suggests that if everything else looks fairly equal and there is a study that shows that aluminum results in higher GHG emissions, “It might tip the decision one way rather than another.”

To the way of steel. And they have the GHG data to prove it.