Carbon Group Publication: Structural Materials and Global Climate

Our publication Structural Materials and Global Climate is now available for purchase!

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Project: Thermal Break Strategies for Cladding Systems in Building Structures

Check out this developing project!

http://www.coe.neu.edu/Research/thermal-breaks/project_summary.html

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Carbon Group Post 4: Do you know how to achieve a carbon-efficient steel-framed building? Your fabricator does.

A common misconception within the Architecture/Engineering/Construction community is that structural steel is a carbon-intense, “dirty” product which sabotages the natural environment by utilizing large amounts of mined content.  In reality, the steel structure being fabricated for your current project has a decent chance of containing metal from a car similar to the one you were driving when you were 16.  

Figure 1 - The structural steel life cycle Credit: American Institute of Steel Construction

Domestic structural steel and rebar are produced with an average of 90% recycled content.  The process in which they are produced transitioned in the late 1970s from the Basic Oxygen Furnace (BOF) process to the Electric Arc Furnace Process (EAF).  This shift resulted in a 24-fold increase in productivity - from 12 hours per ton of steel to one-half of an hour per ton.  Steel products are also transported efficiently in the US, with the majority of steel being transported via barge or rail rather than truck.

Some lighter gage material, like decking and light gage studs, as well as Hollow Structural Sections (HSS) are made via both EAF and BOF.  The BOF process utilizes approximately 30% recycled content.   It is important to be able to differentiate between production processes for all types of steel used on your project when accounting for the carbon impact.  (In this post, as well as the carbon working group white paper, the term “carbon” is used to mean “carbon-dioxide equivalent.”) Versions 2 and 3 of the LEED rating system assume a 25% recycled content for all steel products as a default unless documentation via mill-specific data is provided.  In LEED v4, mill-specific recycled content data can be used to achieve the Leadership Extraction Practices option of the Building Product Disclosure and Optimization credit. 

The cradle-to-gate Environmental Product Declarations (EPDs) released by the American Institute of Steel Construction (AISC) in 2016 for fabricated hot-rolled structural shapes, fabricated HSS, and fabricated plate material provide a full accounting of material sourcing, production, transportation to fabrication shop, and labor and processing in the shop. However, only fabricators who were members of the Institute when it was produced (or have since joined and submitted environmental data) are able to legally use these EPDs to account for carbon content on their structures.

The EPD for Fabricated Hot-Rolled Structural Sections gives results for the impact category of Global Warming Potential (GWP) as 1.16 tons CO₂e per ton of steel produced, with approximately 85% of the total impact coming from the furnace production process.  With the material production impact being the dominant contributor to the total impacts, it is important to be sensitive to overall material use when lessening carbon impacts is the overall goal.  

Figure 2 - Comparison of structural steel frame in the Empire State building as constructed in 1931 vs. now.  Carbon emissions numbers include material production only.  Credit: American Institute of Steel Construction

Material, however, is only one side of the coin regarding overall sustainability.  An argument can be made that designing an erection-friendly structure can also lessen carbon impacts by reducing schedule and saving weeks of labor in the field, although this has yet to be quantified by an official EPD or Life Cycle Analysis (LCA).   

In order to find the “sweet spot” where material efficiency, up-front cost, life-cycle cost, and resiliency come together, one needs to discuss specific project goals with the structural steel fabricator as early as possible – preferably as a preconstruction partner.  The fabricator will be able to educate the design team on local material supply, desired connection schemes, how material can most efficiently run through their shop, as well as be efficiently sequenced in the field. They can aid in implementing green goals such as overall material reduction (both with a material efficient structure and by exposing structure to reduce finishes), material reuse, and integrated process credits. 

The Steel chapter of the upcoming White Paper “Structures and Carbon” describes and compares production processes used domestically.  Specific strategies to produce a carbon-efficient structure are presented.  We look forward to your reviews and comments!

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Carbon Group Post 3: Example Demonstrating How SCMs Can Reduce Embodied Impacts of a Concrete Building

This is the third in a planned series of blog posts on topics that are discussed in depth in the SEI Sustainability Committee’s forthcoming technical report, Building Structure and Global Climate, due out later this year.

In this example, a cradle-to-gate LCA was conducted to determine the embodied impacts of concrete on a building to compare the Global Warming Potential (GWP) of a reference building using typical concrete mixes with moderate amounts of Supplementary Cementitious Materials (SCMs) such as fly ash and slag and a proposed building using concrete mixes that have relatively high volumes of fly ash and slag. The building is an 18 story residential tower located in the northeast United States. Compressive strengths for each structural element are identified in Figure 1.

Figure 1. Specified compressive strength of concrete for an 18 story residential tower.

The first step in the analysis is to identify typical concrete mixes for the reference building. In 2014 (updated in 2016), National Ready Mixed Concrete Association (NRMCA) published benchmark mix designs and their environmental impacts for eight different regions in the United States (www.nrmca.org/sustainability). This example uses the benchmark mix designs for the Northeast region. 

The next step is to estimate mix designs that have significantly lower GWP than the benchmark mixes that still meet the performance criteria (strength, durability, etc.). This example uses high volume SCM mixes from the NRMCA Industry-Wide Environmental Product Declaration (EPD). A summary of the concretes selected for the reference and proposed building are provided in Tables 1 and 2.

Table 1. Mix designs selected for the reference building (from NRMCA benchmark report)

Concrete Element	Specified Compressive Strength (psi)	Portland Cement (lbs/yd3)	Slag (lbs/yd3)	Fly Ash (lbs/yd3)	SCM content
Mat Foundation	6000	782	119	82	20%
Basement Walls	5000	741	112	78	20%
Floors B2-1	5000	741	112	78	20%
Floors 2-18	5000	741	112	78	20%
Shear Walls	6000	782	119	82	20%
Columns	8000	967	147	102	20%

Table 2. Mix designs selected for the proposed building

Concrete Element	Specified Compressive Strength (psi)	Portland Cement (lbs/yd3)	Slag (lbs/yd3)	Fly Ash (lbs/yd3)	SCM Content
Mat Foundation	6000 psi	256	342	256	70%
Basement Walls	5000 psi	242	323	242	70%
Floors B2-1	5000 psi	512	0	341	40%
Floors 2-18	5000 psi	581	0	249	30%
Shear Walls	6000 psi	427	256	171	50%
Columns	8000 psi	503	302	201	50%

Using the Athena Impact Estimator for Buildings (Athena IE) software (www.athenasmi.org), the reference building and proposed building were defined using the proposed mixes in Table 1 and 2 respectively. Athena IE has the NRMCA benchmark mixes and the NRMCA Industry-Wide EPD mixes pre-loaded into the software. The software also permits the user to define new mixes based on the existing mixes in the library or completely new mixes if that information is available from a concrete producer.

Once all the concrete information is defined for each project, the user can then run a report that will provide the estimated GWP, along with other impacts, for each building. The reference building will represent the largest impacts and the proposed designs will represent lower impacts. The results for this example showed that the reference building has a GWP for concrete of 6.14 million kg CO₂ while the proposed building has a GWP for concrete of 3.92 million kg CO₂ meaning that the high volumes of fly ash and slag mixes resulted in 36% reduction in GWP as shown in Figure 2.

Figure 2. Summary of GWP for reference building and proposed building.

Keep in mind, this is example was simplified for illustration purposes. It only considered the effects of concrete during the material extraction and manufacturing stage on the environmental impacts of the building. The Athena IE software does contain environmental impact information for most materials and products used in buildings and allows input of operational energy data for conducting a more comprehensive whole building LCA.

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Carbon Group Post 2: What About the Data?

Carbon Group Post 2: What About the Data?

This is the second in a planned series of blog posts on topics that are discussed in depth in the SEI Sustainability Committee’s forthcoming technical report, Building Structure and Global Climate, due out later this year.

As with all analyses, the quality of environmental assessment results depends greatly on the quality of the input data. What we learned in our earliest structural engineering and computer programming courses holds true: garbage in = garbage out. When it comes to environmental analyses of our structures, no matter the level of detail of the analysis—carbon dioxide equivalent footprint (carbon footprint), life-cycle inventory, or life-cycle analysis (LCA)—quality input data is important to achieve credible, verifiable, and consistent results.

Uncertainty in analyses related to data quality and variability is important enough that an entire chapter of the SEI Sustainability Committee’s forthcoming technical report is devoted to the topic. In this post, I’ll highlight the key questions to ask related to data when evaluating a carbon footprint.

Data quality and variability

When performing a carbon footprint, data typically can be taken from a few different types of sources:

·         Public databases

·         Private databases

·         Primary data

A public database is usually managed by an association or a public or private institution. In the U.S., one public database is the U.S. LCI database and it is managed by NREL. Private databases can belong to large consulting firms that have performed multiple LCAs or software companies. Lastly, primary data can be obtained directly from product manufacturers. These data are the most applicable to the analysis, yet they are typically the most time consuming and expensive to get. In all cases, data for use in carbon footprint studies includes quantities of materials and energy that go into the system boundary being studied, and emissions to land, water, and air that come out of the system boundary.

Regardless of the source, data used in carbon footprints should be accompanied by evaluations of data quality and variability. Unfortunately, most LCI datasets do not include statistical variability. Information such as standard deviation and statistical distribution can be useful when evaluating or comparing carbon footprints. When evaluating an LCA report or EPD, research whether average data from public or private databases is representative of the industry. Keep relative uncertainty and statistical significance in mind when using data and results. Another way to check reliability of results is to request uncertainty/variability information from suppliers and trade organizations.

Data quality guidance is given in ISO standard 14044, Environmental Management-Life Cycle Assessment-Requirements and Guidelines. Typical factors that are addressed include: the timeliness, geographic and technical relevance, precision, completeness, representativeness, consistency, reproducibility, sources, and uncertainty of the information (for example, data, models, and assumptions).

This brief introduction to data quality and variability for carbon footprints will hopefully give you some indicators to look for the next time you read one of these studies. 

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Carbon Group Post 1: Why Climate Change Matters

Structural Materials and Global Climate: Why Climate Change Matters

The Carbon Task Group of the Structural Engineering Institute’s Sustainability Committee has spent years studying the ways structural materials and systems affect climate change. This is the first of a planned series of blog posts on topics discussed in depth in our forthcoming technical report.

Why should we care about climate change? How bad could it be? Warmer winters will be nice, right?

We all know what’s happening. Among other things, people are burning a lot of fossil fuels—coal, oil, gas—sending unprecedented quantities of carbon dioxide and other greenhouse gases into the atmosphere. These heat-trapping gases are raising the temperature of our air and oceans, and increasing the ocean’s acidity. Polar ice is melting, contributing to sea level rise. Some regions are experiencing more intense storms and more frequent droughts. Coral reefs are dying. But so what, we can adapt, you might think. Well, maybe, but it would not be easy and the risks are great.

Even if you don’t live by the ocean or in a place where water shortages may become commonplace, there’s a lot to worry about. Climate change promises to be politically destabilizing, as millions of people find their homes inundated or food supplies threatened. They will need to resettle, increasing the flow of refugees. Political instability will lead to conflict, and yet more refugees. The Pentagon considers climate change a major risk, an “accelerant of instability” and a “threat multiplier.” We will all be affected.

And changes are coming fast. A recent study found that the United States is likely to reach an average temperature increase of at least 2°C by 2035, nearly 15 years earlier than the prediction for the globe as a whole, and that there’s at least a 50-50 chance that the northeast could reach this dubious milestone in only 10 years (Figure 1). Coastal cities such as Boston are talking about taking extreme measures to control advancing seas, such as constructing a four-mile-long, 20-foot high, barrier wall around the harbor to protect the low-lying areas of the city (Figure 2).

But the most unsettling changes are not inevitable. We still have a short amount of time to mitigate such worst-case outcomes, and structural engineers have a key role to play. We will explore what we can do in coming blog posts, so stay tuned.

Figure 1 shows the range of climate model predictions for the timing of temperature increases in the northeastern United States, the United States as a whole, and the world as a whole. The vertical axis represents the percentage of climate models that predict a given temperature will be reached by a given year.

Figure 2 shows a proposed 4-mile-long barrier wall to protect the city of Boston (Boston Globe, 17 February 2017).

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2016 Geo-Structures Presentations

The ASCE-SEI Sustainability Committee and the ASCE Geo-Institute Sustainability in Geotechnical Engineering Committee had a very successful 2016 Geo-Structures Congress. We are happy to report that the two committees had representation at five sessions; they presented on various aspects of sustainable design. Since one of our main committee goals is to spread the word on sustainable design aspects that the practicing structural engineer can put to use, we’re posting the presentations here on our website. Have any questions on these presentations or on how to make your designs more sustainable, please comment below or contact Dave DeLong. Online copies of all of the following presentations are available here.

Track: The SEI Climate Action Initiative

‘Introduction/The Role of the Structural Engineer’ by Jim D’Aloisio

Raise awareness of the importance of climate change mitigation and adaptation by structural engineers, and share mitigation and adaptation ideas and strategies with the structural engineering community

’Mitigation of Emissions During Construction’ by Megan Stringer

My presentation discussed how engineers can quantify and reduce the embodied energy and emissions from buildings. 

‘Rationale for Concern’ byMark Webster

'Mitigation of Emissions During Building Operation'  by Dave DeLong

'The decisions that structural engineers make in detailing the building envelope can influence the building's R-value by a great degree. By detailing to increase this R-value, structural engineers can reduce the heating and cooling loads - and, as a result, the carbon impact - of the building over its service life

Track: Disaster Resilience – Indispensable for Sustainable Design

‘Introduction / Incorporating Life Cycle Assessment with Disaster Resilience’ by Tona Rodriguez-Nikl

An introduction to the session, putting forward the argument that disaster resilience must be considered as part of sustainable design. / A summary of recent efforts to integrate life cycle assessment with disaster risk methodologies. The goal of these studies is to quantify how different levels of disaster resistance affect environmental life cycle impacts.

‘Resilient Design Strategies for Structural Engineers

My presentation discussed resiliency, why it matters to structural engineers and how engineers can design resiliently. The presentation also reviewed current legislation, organizations, and rating systems that deal with resiliency. 

‘Learning to Survive: A global comparison of recovery from disasters’ by Erica Fischer and Sal Gimbert-Carter

Disasters have catastrophic impacts on countries economically, socially, culturally, and politically. This presentation compares how three different countries responded to three different disasters: 2004 Summatra Earthquake and Tsunami in Indonesia, 2005 Hurricane Katrina in New Orleans, and 2010-2011 Christchurch Earthquake Sequence in New Zealand.

 

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