Achieving Net Zero Embodied Carbon In Structural Materials .
Achieving Net Zero EmbodiedCarbon in Structural Materialsby 2050403530252015105020102020203020402050A White Paper by the Structural Engineering Institute’s SustainabilityCommittee Carbon Working GroupMark D. Webster, EditorMarch 2020Updated May 2020Image inspired by Figure SPM.3a from IPCC Report Global Warming of 1.5 C (2018)https://report.ipcc.ch/sr15/pdf/sr15 spm final.pdf
Achieving Net Zero Embodied Carbon in Structural Materials by 2050Executive SummaryStructural materials (i.e., steel and concrete) are responsible for over 10% of global carbondioxide emissions. This paper outlines five paths to achieve a net zero-carbon future within thebuilt environment. These paths include varying levels of adoption of 4 transition tracks: (1)design improvements, (2) greening the electrical grid, (3) material production improvements,and (4) carbon offsets.Through design optimization, we estimate that between 10% and 25% of emissions can beavoided relative to current practices. Ways in which these emissions can be reduced includethe avoidance of over-design, topology optimization, and performance-based design. Likewise,we estimate another 10% to 25% reduction in carbon emissions may be possible by specifyingthe appropriate materials. For example, concrete mix designs of the same compressive strengthcan vary significantly in their carbon emissions. Selecting concrete mixtures for both theirstructural and environmental performance can help structural designers reduce the carbonemissions of their structural systems by up to 40%. In addition, by reducing construction waste,for example through modular construction, we estimate between 5% and 10% reductions incarbon emissions can be achieved. Often the most effective design strategy to reduce carbonemissions from structural systems is to avoid new construction through retrofit and the adaptivereuse of existing buildings. Through retrofit, we estimate that between 5% and 15% of structuralsystem carbon emissions could be reduced. Another design strategy to reduce carbonemissions is the use of substitute structural systems. By building with biogenic carbon (e.g.,wood and straw), we estimate potential reductions in carbon emissions between 15% and 25%.Finally, design for resilience may be a contributing strategy, but insufficient research is availableto estimate how much this strategy may contribute to embodied carbon reductions by 2050. Thestructural engineering community's adoption of these design optimization strategies has thepotential to reduce carbon emission between 10% and 55%, showing a significant potential forreductions between present day and 2050.By transitioning the electrical grid from non-renewable, carbon-intensive energy sources torenewable, carbon-free energy, the embodied carbon of structural materials could be reducedby 5% to 10%. Currently, the United States' electrical grid is already becoming increasinglycarbon-free due to the decline of coal and state legislation requiring more electricity to beobtained from renewable energy sources. Overall, the reduction of embodied carbon from arenewable electric grid would vary depending on the material type. For structural steel, AISCestimates that carbon-free electricity would reduce the embodied carbon of steel byapproximately 50%. However, for concrete, the embodied carbon reduction due to carbon-freeelectricity would only be approximately 6%.Improvements in the production of structural materials could provide an embodied carbonreduction ranging from 10% to 30%. Currently, material manufacturers have been steadilySEI Sustainability Committee1.May 2020
Achieving Net Zero Embodied Carbon in Structural Materials by 2050reducing the unit carbon footprints of their products over the past decades by incorporatingmore efficient manufacturing technologies. The carbon intensity of cement in the US hasreduced by 33% within the past 50 years, though most U.S. production is already using modern,energy-efficient kilns so additional progress will likely not be as rapid moving forward. Thegreatest promise for U.S. concrete production is a move towards blended cements, such asthose popular in the European markets. For steel manufacturing, the energy intensity droppedby 10% between 1990 and 1998. However, the rate of reduction is slowing due to the minimumtheoretical energy required to produce steel. For wood products, carbon reductions are likely tocome from sustainable forestry management practices, better understanding and measurementof carbon sequestration, and future harvesting and manufacturing efficiencies.The final option to achieve net zero carbon emissions is the use of carbon offsets. Carbonoffsets are investments in actions that reduce carbon emissions and should be third-partyverified.Combining design strategies, electrical grid improvements, and manufacturing improvements,the built infrastructure can transition to net zero carbon emissions by 2050 even without the useof carbon offsets.SEI Sustainability Committee2.May 2020
Achieving Net Zero Embodied Carbon in Structural Materials by 20501. IntroductionThe Intergovernmental Panel on Climate Change (IPCC) has determined that to limit globalwarming to 1.5 C we must reduce CO2 emissions by 45% from 2010 levels by 2030 and to netzero by 20501. For buildings, this means we must work towards reducing the CO 2e2 emissions(“carbon” emissions, also called Global Warming Potential (GWP)) associated with materialsand construction (“embodied carbon”) to zero. How can structural engineers help accomplishthis objective?The SEI Sustainability Committee’s Carbon Working Group (CWG) is studying this issue. Thispaper primarily addresses structural materials, although other design professionals—especiallyarchitects—will need to play a central role. Structural materials represent half or more of theembodied impacts of most new buildings,3 and an even higher proportion of most infrastructureprojects such as bridges and dams, so structural engineers must be leaders in the essentialtransition to net zero embodied carbon and beyond to net-positive carbon-sequestering design.We identified four transition tracks that have the ability to reduce carbon emissions associatedwith structural materials:1. Design Improvements: Structural engineers must make design choices and otherdesign improvements, such as material selection and optimization, that reduce thecarbon emissions of new construction.2. Greening the Electrical Grid: The electrical power used to manufacture buildingmaterials must continue to transition towards renewable sources.3. Material Production Improvements: Material producers must continue to reduce thecarbon emissions associated with manufacturing processes and work towardsdesigning products and materials that durably store carbon.4. Carbon Offsets: Any remaining carbon emissions must be offset with investments invalidated near-term carbon reduction projects.Carbon sequestration and storage in building materials will be essential to achieve net zerocarbon without relying on offsets. Carbon storage includes the temporary removal of carbon1IPCC, 2018: Summary for Policymakers. In: Global Warming of 1.5 C. An IPCC Special Report on theimpacts of global warming of 1.5 C above pre-industrial levels and related global greenhouse gasemission pathways, in the context of strengthening the global response to the threat of climate change,sustainable development, and efforts to eradicate poverty [Masson-Delmotte, V., P. Zhai, H.-O. Pörtner,D. Roberts, J. Skea, P.R. Shukla, A. Pirani, W. Moufouma-Okia, C. Péan, R. Pidcock, S. Connors,J.B.R. Matthews, Y. Chen, X. Zhou, M.I. Gomis, E. Lonnoy, T. Maycock, M. Tignor, and T. Waterfield(eds.)] (https://www.ipcc.ch/sr15/chapter/spm/).2CO2e refers to CO2 equivalent. Emissions other than carbon dioxide, such as methane, alsocontributes to global warming. CO2e includes the effect of these other emissions normalized to CO 2.3See e.g. Strain, Larry. Time Value of Carbon, Carbon Leadership Forum white paper, May he-time-value-of-carbon/).SEI Sustainability Committee3.May 2020
Achieving Net Zero Embodied Carbon in Structural Materials by 2050from the atmosphere in products such as wood framing which will eventually return to theatmosphere at building end-of-life. Carbon sequestration refers to the more permanent removalof carbon, for example in chemical reactions that lock the carbon into the molecular matrix of amaterial.“Carbon sequestration and storage in building materials willbe essential to achieve net zero carbon without relying onoffsets.”Carbon can be stored in wood and agricultural products, but careful consideration of their supplychains is essential in order to be effective in reversing climate disruption. Timber harvestingcauses an uptick in carbon emissions, mostly due to soil exposure, that can take many years torecover. Experts argue that only wood extracted from sustainably managed forests, such asthose certified by the Forest Stewardship Council, are a climate-friendly material choice.Agricultural products made into building materials, such as straw and hemp, more clearlysequester carbon in the near-term because of the annual growing cycle. Designers can selectsuch products to reduce the carbon footprint of their projects.Material producers can also sequester carbon in their products. Some companies are alreadyoffering such technology for concrete and aggregate production.4 Others are sure to follow.The path to net zero embodied carbon will surely include various combinations of thesetransition tracks. We offer five possibilities, as outlined in Table 1-1 and Figure 1-1. Many othercombinations are possible. We examine the potential for each track later in this paper.4Sequestration possibilities include the development of carbon capture and storage technology atproduction facilities such as cement kilns. Product examples include Blue Planet, which is soon to becommercially available but already performing very well in trials at the San Francisco airport. BluePlanet captures emissions and turns them back into limestone aggregate for new concrete, heraldingthe possibility of truly carbon-sequestering concrete. Technologies which incorporate organic matterinto stable inorganic matrices such as hempcrete also qualify.SEI Sustainability Committee4.May 2020
Achieving Net Zero Embodied Carbon in Structural Materials by 2050Design sTrackDesign Dominant45%5%10%40%Electricity and MaterialProduction Dominant20%10%25%45%Strong Multi-Trackwithout Sequestration45%10%25%20%Strong Multi-Track withSequestration55%10%35%0%Status Quo10%5%10%75%Path IDTable 1-1: Some Possible Combinations of Transition Tracks to Get to Zero Embodied CarbonFigure 1-1: Some of the Possible Paths to Net Zero Embodied Carbon by 2050. Each barrepresents different combinations of the four available reduction tracks.The first two paths in the table and figure include strong action in some but not all the tracks.The third path represents strong action in all three tracks, but without sequestration, andtherefore leans on offsets to make up the difference. The fourth path is the most desirable:strong action on all tracks as well as sequestration to compensate for remaining emissionsSEI Sustainability Committee5.May 2020
Achieving Net Zero Embodied Carbon in Structural Materials by 2050rather than offsets. The final path represents the business-as-usual scenario, where emissionscontinue to drop at a slow rate, necessitating major investments in offsets to get to net zero.Status of Construction in the United StatesTo plot a route to net zero embodied carbon, we must understand where the opportunities lie.We used public information from the U.S. Census Bureau5 and the U.S. Energy InformationAdministration’s Commercial Buildings Energy Consumption Survey (CBECS)6 to estimate theproportion of construction in the commercial and residential sectors by structural frame type, asshown in Figure 1-2. The data shows that about two-thirds of new construction is in theresidential sector and one-third in the commercial sector. Residential construction is dominatedby wood-framed single-family homes. Most commercial construction is steel- and concreteframed.Figure 1-2: Annual New Construction in the United States by Building Type and Type ofStructural Frame5U.S. Census Bureau, New Residential Construction, html.6U.S. Energy Information Administration, Commercial Buildings Energy Consumption Survey, I Sustainability Committee6.May 2020
Achieving Net Zero Embodied Carbon in Structural Materials by 2050“.about two-thirds of new construction is in the residentialsector and one-third in the commercial sector.”We estimated the U.S. consumption of the primary structural materials—concrete, steel, andwood—in building construction using data from the American Institute of Steel Construction,7the National Ready Mix Concrete Association,8 and the Forest Products Lab.9 Using informationfrom industry-average Environmental Product Declarations (EPDs), we estimated the carbonemissions associated with these materials, as shown in Figure 1-3. Unlike Figure 1-2 which isby framing type, Figure 1-3 includes all concrete whether the building is steel-framed, woodframed, or concrete-framed, including concrete foundations and floors. (It bears noting thatalmost all new buildings use at least some wood, steel, and concrete; we designate them aswood, concrete, or steel structures based on which material predominates in the structuralsystem.) We see that the emissions associated with concrete, even without including plantmixed precast concrete and steel reinforcement, account for over three-quarters of the totalemissions associated with these three materials. Although most single-family homes areconstructed with wood framing, the contribution of wood to carbon emissions is small relative tothe emissions associated with concrete in these structures.10 The carbon emissions fromresidential construction exceed the emissions from commercial construction. Although structuralengineers play a limited role in most residential construction projects, this sector must beaddressed.“.the emissions associated with concrete.account forover three-quarters of the total emissions associated withthese three materials.”7American Institute of Steel Construction, Structural Steel: An Industry Overview, August, 2018.National Ready Mixed Concrete Association, Historical US Ready Mixed Concrete Production,unpublished, provided 14 March 2019.9United States Department of Agriculture, Forest Products Laboratory, U.S. Forest Products AnnualMarket Review and Prospects, 2013–2017, Research Note FPL–RN–0348, July 2017.10The wood EPDs that are the data source for this assessment treat biogenic carbon emissions ascarbon neutral.8SEI Sustainability Committee7.May 2020
Achieving Net Zero Embodied Carbon in Structural Materials by 2050Figure 1-3: Annual CO2e Emissions Associated with Structural Materials Used in NewConstruction in the United States by Building SectorSEI Sustainability Committee8.May 2020
Achieving Net Zero Embodied Carbon in Structural Materials by 20502: Reduced Carbon Footprint through DesignDesigners have the most control over reducing the embodied carbon of the buildings theydesign. This section provides a roadmap of different measures that designers can use to reducethe embodied carbon intensity of buildings. This section briefly introduces strategies, leaving itto the structural engineer and design team to determine which are best employed for theirproject. More comprehensive discussions of each of these strategies are included in the WholeBuilding LCA Practice Guide11 published previously by the committee.Design OptimizationDesign teams can optimize their designs to reduce their structures’ embodied carbon. Manydesign strategies exist, such as optimizing column grid layout and beam spacing to minimizethe total weight of materials used. Material quantity reduction strategies are often building andarchitecture specific, yet general principles apply for different materials. Some strategies forreducing material quantities for the three main structural materials follow:Concrete: Utilize voided slab systems or post-tensioned slabs to reduce totalconcrete quantities, and/or use higher strength concrete (but also accounting forthe increased environmental impacts). Also, slabs on grade and foundation wallscan sometimes be made thinner without reduction in performance, and the useof frost-protected shallow foundation designs can reduce required concretefoundation volume by 50% or more.Steel: Utilize composite design, braced frames instead of moment frames, longspan deck systems to eliminate intermediate framing, and/or lightweight concreteto reduce the weight of the structure. Also, the use of optimized element sizesrather than keeping all elements of similar size, can reduce steel tonnage eventhough this may not be the least expensive option.Wood: Optimize framing from a value engineering perspective to reduce the totalvolume of wood. These techniques, often described as “Optimum ValueEngineering” or “Advanced Framing,” include incorporating single top plates, 24inch stud spacing, eliminating headers in non-load-bearing walls, and using twostuds at corners. Further information is available at the APA website12 andelsewhere.Masonry: If possible, designing masonry walls without steel reinforcementeliminates the footprint of the grout, which is essentially a cement-rich flowable11Yang, F. (Ed.). (2018). Whole Building Life Cycle Assessment: Reference Building Structure andStrategies. American Society of Civil Engineers. Access at: .apawood.org/advanced-framingSEI Sustainability Committee9.May 2020
Achieving Net Zero Embodied Carbon in Structural Materials by 2050concrete, as well as the reinforcing bars. If reinforcement is required, usepartially-grouted masonry walls over fully-grouted.These savings can be evaluated using LCA. The reader is referred to the WBLCA PracticeGuide produced by the SEI Sustainability Committee previously referenced.Supporting ResearchKaethner & Burridge (2012) studied three commercial building types from cradle-to-site usingalternative structural systems (steel-framed, concrete-framed, and long-span) and found thatno particular structural system was consistently the lowest in embodied carbon. The margin ofuncertainty due to variability in material impact factors was greater than any advantage betweenstructural materials. However, once a structural system was chosen, Kaethner & Burridge foundthat there was significant opportunity for embodied carbon reduction through carefulspecification and efficient design. Kaethner & Burridge found that the embodied carbon of thebuilding’s structure was more than half the embodied carbon of the entire building and thatadding a long-span scheme added about 10% to the whole building impact.Research shows that there is a large opportunity to reduce embodied carbon by increasing theefficiency of steel design. Moynihan & Allwood (2014) found in a study of 23 steel buildingswith more than 1,000 steel beams that the average beam utilization was below 50%. Repetitionacross floor plates eases the design and fabrication burden; Moynihan & Allwood found that inthe buildings studied, 5 beam sizes accounted for more than 75% of the beams in the floorplates, suggesting many buildings are designed based on worst-case loading. Thirion (2012)explored the reduction in embodied carbon possible if a steel cross section is varied along itslength and found the potential reduction is up to 30%. Thirion acknowledges, however, that alarge portion of this reduction is due to the overdesign of steel beams, similar to Moy
Achieving Net Zero Embodied Carbon in Structural Materials by 2050 SEI Sustainability Committee 1. May 2020 Executive Summary Structural materials (i.e., steel and concrete) are responsible for over 10% of global carbon dioxide emissions. This paper outlines five paths to achieve a net zero-carbon future within the built environment.
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Net Zero and the NHS THE EMISSIONS CHALLENGE Building design in the UK faces an unprecedented . Typically, the procurement and travel components of carbon make up circa 75% to 85% of total operational carbon. OPERATIONAL CARBON SPLIT The split of embodied carbon on a non-domestic project varies depending on the type of project.
from a climate perspective is carbon foot-print. A building carbon footprint includes both operation emissions and the emissions associated with producing the material. A building material carbon footprint is often referred to as “embodied carbon.” Note that embodied carbon refers to th
The Net-Zero riteria are part of the STi’s Net-Zero Standard. The Net-Zero Standard, which entails both the Criteria and forthcoming Net-Zero Guidance, will be finalized by November 2021 in advance of the 2021 United Nations Climate Change Conference (COP26). Public consultation of the Net-Zero Guidance is scheduled to begin in July 2021.
List of Figures, Tables and Boxes Figures 2 Figure S1 Overview of the key nuances of net-zero target implementation approaches 5 Figure S2 Ten basic criteria for net-zero target transparency 14 Figure 1 Internet searches for net-zero emissions 15 Figure 2 Map of cities and regions pursuing net-zero emissions 16 Figure 3 Population of cities and regions with net-zero targets, by geographic region
emissions ('net zero emissions') has grown, so has the need for a common understanding on what net zero emissions means and how to achieve net zero goals. Investors are also putting pressure on companies to lay out their plans for reaching net zero emissions and to demonstrate how net zero pathways are integrated into their long-term strategy.4
China net zero and job creation: Potential for the creation of c.40 mn jobs by 2060 33 Laying out the path to a net zero China: A sectoral deep dive 34 China net zero: The role of carbon sequestration 61 China net zero: The potential implications for natural resources demand 64
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