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The role of biobased building materials in the climate impacts of construction: Effects of increased use of biobased materials in the Swedish building sector
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials. RISE - Research Institutes of Sweden. (Civil and Architectural Engineering)ORCID iD: 0000-0003-3140-6823
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

A significant share of the global climate change impacts can be attributed to the construction sector. One mitigation strategy is increasing the use of biobased materials. Life cycle assessment (LCA) has been used to demonstrate the benefits of this, but forest complexities create uncertainty due to omission of key aspects. The aim of this thesis is to enhance understanding of the effects of increasing use of biobased materials in climate change mitigation of construction works with a life cycle perspective. Non-traditional LCA methodology aspects were identified and the climate impact effects of increasing the use of biobased materials while accounting for these was studied. The method applied was dynamic LCA combined with forest carbon data under multi-approach scenarios. Diverse case studies (a building, a small road bridge and the Swedish building stock) were used. Most scenarios result in impact reductions from increasing the use of biobased materials in construction. The inclusion of non-traditional aspects affected the results, but not this outcome. Results show that the climate mitigation potential is maximized by simultaneously implementing other strategies (such as increased use of low-impact concrete). Biobased building materials should not be generalised as climate neutral because it depends on case-sensitive factors. Some of these factors depend on the modelling of the forest system (timing of tree growth, spatial level approach, forest land use baseline) or LCA modelling parameters (choice of the time horizon, end-of-life assumptions, service life). To decrease uncertainty, it is recommended to use at least one metric that allows assessment of emissions based on their timing and to use long-term time horizons. Practitioners should clearly state if and how non-traditional aspects are handled, and study several methodological settings. Technological changes should be accounted for when studying long-term climate impacts of building stocks.

Abstract [sv]

Irreversibel global påverkan på klimat och miljö måste undvikas och olika strategier som begränsar klimatförändringarna kan utnyttjas för att hantera denna utmaning. En betydande andel av de globala utsläppen av växthusgaser kan hänföras till byggsektorn i allmänhet och cementproduktion i synnerhet, och begränsningsstrategier söker alternativ till fossil- och mineralbaserade resurser, med mindre påverkan, som exempelvis en ökad användning av biobaserade material i byggandet. Livscykelanalys (LCA) har använts för att demonstrera klimatnyttan av denna ökning, men skogens komplexiteter i samband med biogent koldioxid skapar osäkerhet i resultaten då de som genomför LCA-studier traditionellt utelämnar viktiga nyckelaspekter.

Denna avhandling syftar till att öka förståelsen för effekterna av en ökad användning av biobaserade material för begränsning av byggandets klimatpåverkan i ett livscykelperspektiv. Forskningsfrågorna formulerades med fokus på att identifiera icke-traditionell LCA-metodik, samt att bedöma miljöeffekterna av en ökad användning av biobaserade material med redovisning av dessa aspekter på olika nivåer, gällande enstaka konstruktioner och byggnadsbeståndet som helhet. Den metodik som används är dynamisk LCA i kombination med data om skogskolbalans, med analyser av flera scenarier med olika metodologiska antaganden. Fallstudier med olika kännetecken användes, nämligen en byggnad, en bilvägsbro och en uppskattning av det svenska byggnadsbeståndet på lång sikt.

Resultaten bekräftar att en ökad användning av biobaserade material minskar klimatpåverkan av byggandet – en tydlig majoritet av de scenarier som analyserats för alla fallstudier resulterar i sänkt klimatpåverkan. Införandet av icke-traditionella LCA-aspekter påverkar resultatet, men förändrar inte att en ökad användning av biobaserade material resulterar i lägre långsiktig och kumulativ klimatpåverkan. Resultaten visar också att den maximala klimatbegränsningspotentialen endast nås genom att samtidigt införa andra tekniska lösningar med lägre klimatpåverkan. När det gäller LCA-metodik visar resultaten att antagandet att biobaserade byggnadsmaterial är klimatneutrala är en överförenkling eftersom deras klimatpåverkan beror på fallspecifika faktorer och därför bör inga generaliseringar göras. Några av dessa klimatpåverkande faktorer beror på modellering av skogssystemet i en dynamisk LCA; såsom när skogstillväxten antas börja i förhållande till avverkningen, den geografiska upplösningen för att analysera de biogena kolflödena dvs. som ett avverkningsbestånd eller på landskapsnivå och vad utgångsläget sätts till vid analys av skogens markanvändning. Andra faktorer beror på LCA-modellering, nämligen valet av integrerad tidshorisont för beräkning av klimatpåverkan, det antagna scenariot för avfallshantering och lagringsperioden för det biogena kolet i tillverkade produkter.

För att minska osäkerheten i bedömning av klimatpåverkan av biobaserade byggmaterial rekommenderas användning av minst en mätmetod som gör det möjligt att bedöma koldioxidutsläppen baserat på tidpunkten på dessa, samt att tillämpa mätvärden med långa tidsperspektiv. Redovisning av icke-traditionella aspekter har en betydande effekt på klimatpåverkan av biobaserade byggmaterial. Utförare av analyser rekommenderas därför även att redovisa hur dessa aspekter hanteras och att ställa upp flera olika scenarier och analysera dessa med flera olika metodologiska inställningar. Slutligen rekommenderas att ta hänsyn till den tekniska utvecklingen vid analyser av långsiktig klimatpåverkan av byggnadsbeståndet som genomförs med dynamiska värden för processer som äger rum i framtiden.

Abstract [es]

Para evitar impactos irreversibles a nivel global, es necesario mitigar el cambio climático. Una parte significativa de las emisiones globales de gases efecto invernadero puede atribuirse al sector de la construcción y la producción de cemento. Entretanto, se busca implementar estrategias de mitigación de bajo impacto, tal es el caso de incrementar el uso de materiales de origen forestal. El análisis de ciclo de vida (ACV) se aplica con frecuencia para demostrar los beneficios climáticos de este incremento, pero las complejidades relacionadas con el bosque y el carbono biogénico crean incertidumbre ya que los autores normalmente omiten ciertos aspectos clave.

Esta tesis busca mejorar la comprensión de los efectos de un incremento en el uso de materiales de origen forestal en la mitigación del cambio climático en el sector de la construcción, bajo una perspectiva de ciclo de vida. Para ello se han formulado preguntas de investigación centradas en la identificación de los aspectos metodológicos no tradicionales del ACV que pueden afectar el resultado, así como en la evaluación de los efectos ambientales del aumento del uso de materiales biológicos en construcciones o en la construcción en existencia, mientras se toman en cuenta dichos aspectos. Los métodos aplicados incluyen el ACV dinámico en combinación con modelos del balance de carbón en el bosque, además del análisis de múltiples escenarios con diferentes configuraciones metodológicas y asunciones. Se utilizaron casos de estudio con diferentes características y sus respectivos productos equivalentes de referencia; un edificio, un puente para carretera pequeño y la construcción en existencia en Suecia a largo plazo.

Los resultados confirman que el aumento del uso de materiales de origen forestal disminuye el impacto climático de la construcción, ya que la gran mayoría de los escenarios analizados para todos los casos de estudio resultan en reducciones del impacto climático. La inclusión de aspectos no tradicionales del ACV ha influido en los resultados, sin afectar el hecho de que incrementar el uso de material biológico se traduce en menores impactos climáticos acumulados a largo plazo. Los resultados también muestran que el potencial máximo de mitigación climática sólo se alcanza mediante la implementación simultánea de otras tecnologías de bajo impacto. En cuanto a la metodología del ACV, la tesis ilustra que la hipótesis de que los biomateriales de construcción son neutrales respecto a sus impactos climáticos es una simplificación excesiva, y demuestra también que los flujos de carbono biogénico deben ser tenidos en cuenta. El balance de carbono de los materiales de construcción de origen forestal depende de factores relacionados con el sistema forestal que son sensibles las circunstancias del caso de estudio; por lo que no deberían hacerse generalizaciones. De dichos factores, algunos dependen de los modelos usados para simular el sistema forestal; tales como la contabilización del punto temporal de ocurrencia de los flujos de carbono biogénico, la perspectiva espacial para medir estos flujos y la línea de base trazada para el sistema forestal. Otros factores dependen del modelo usado para el ACV, como la elección del horizonte temporal integrado para el cálculo del impacto, el escenario de disposición final y el período de almacenamiento del carbono biogénico en los productos.

Para obtener conclusiones más robustas, se recomienda que los autores de estudios utilicen al menos un método adicional al GWP que les permita evaluar las emisiones de carbono basadas en el punto temporal de su ocurrencia, así como que se apliquen horizontes temporales a largo plazo en el uso de dichos métodos. Tener en cuenta los aspectos no tradicionales estudiados en esta tesis en estudios de ACV de materiales de construcción de origen forestal puede tener una influencia significativa en su impacto climático, por lo que se recomienda que los autores expongan claramente si estos aspectos se incluyen y cómo se incluyen. También se recomienda que se analicen múltiples escenarios con una variedad de configuraciones metodológicas alternativas. Por último, se recomienda tener en cuenta los cambios tecnológicos en los análisis a largo plazo de los impactos climáticos de la construcción en existencia, utilizando factores de impacto dinámico para los procesos que trascurran en el futuro.

Place, publisher, year, edition, pages
Stockholm, Sweden: KTH Royal Institute of Technology, 2017. , 50 p.
Series
TRITA-BYMA, ISSN 0349-5752 ; 2017:02
Keyword [en]
LCA, timber buildings, timber bridges, biobased building materials, dynamic LCA, climate change mitigation, building stock, scenario analysis, biogenic carbon
National Category
Environmental Engineering
Research subject
Civil and Architectural Engineering
Identifiers
URN: urn:nbn:se:kth:diva-207130ISBN: 978-91-7729-418-4 (print)OAI: oai:DiVA.org:kth-207130DiVA: diva2:1096048
Public defence
2017-06-09, Kollegiesalen, Brinellvägen 8, floor 4, Stockholm, 10:00 (English)
Opponent
Supervisors
Projects
EnWoBio - Engineered Wood and Biobased Building Materials Laboratory
Funder
Swedish Research Council Formas, 2014-172
Note

QC 20170517

Available from: 2017-05-17 Created: 2017-05-16 Last updated: 2017-06-29Bibliographically approved
List of papers
1. Climate impact assessment in LCAs of forest products: Implications of method choice for results and decision-making
Open this publication in new window or tab >>Climate impact assessment in LCAs of forest products: Implications of method choice for results and decision-making
Show others...
(English)Manuscript (preprint) (Other academic)
Identifiers
urn:nbn:se:kth:diva-161213 (URN)
Note

QS 2015

Available from: 2015-03-10 Created: 2015-03-10 Last updated: 2017-05-16Bibliographically approved
2. Exploring the climate impact effects of increased use of bio-based materials in buildings
Open this publication in new window or tab >>Exploring the climate impact effects of increased use of bio-based materials in buildings
2016 (English)In: Construction and Building Materials, ISSN 0950-0618, E-ISSN 1879-0526, Vol. 125, 219-226 p.Article in journal (Refereed) Published
Abstract [en]

Whenever Life Cycle Assessment (LCA) is used to assess the climate impact of buildings, those with high content of biobased materials result with the lowest impact. Traditional approaches to LCA fail to capture aspects such as biogenic carbon exchanges, their timing and the effects from carbon storage. This paper explores a prospective increase of biobased materials in Swedish buildings, using traditional and dynamic LCA to assess the climate impact effects of this increase. Three alternative designs are analysed; one without biobased material content, a CLT building and an alternative timber design with “increased bio”. Different scenario setups explore the sensitivity to key assumptions such as the building's service life, end-of-life scenario, setting of forest sequestration before (growth) or after (regrowth) harvesting and time horizon of the dynamic LCA. Results show that increasing the biobased material content in a building reduces its climate impact when biogenic sequestration and emissions are accounted for using traditional or dynamic LCA in all the scenarios explored. The extent of these reductions is significantly sensitive to the end-of-life scenario assumed, the timing of the forest growth or regrowth and the time horizon of the integrated global warming impact in a dynamic LCA. A time horizon longer than one hundred years is necessary if biogenic flows from forest carbon sequestration and the building's life cycle are accounted for. Further climate impact reductions can be obtained by keeping the biogenic carbon dioxide stored after end-of-life or by extending the building's service life, but the time horizon and impact allocation among different life cycles must be properly addressed.

Place, publisher, year, edition, pages
Elsevier, 2016
Keyword
Biogenic carbon dioxide, Climate impact assessment, Dynamic LCA, Life Cycle Assessment, Wood construction, Buildings, Carbon dioxide, Ecodesign, Forestry, Global warming, Wooden construction, Alternative designs, Forest carbon sequestration, Global warming impact, Life Cycle Assessment (LCA), Traditional approaches, Life cycle
National Category
Civil Engineering
Identifiers
urn:nbn:se:kth:diva-195234 (URN)10.1016/j.conbuildmat.2016.08.041 (DOI)000385600100022 ()2-s2.0-84982189595 (Scopus ID)
Note

QC 20161117

Available from: 2016-11-17 Created: 2016-11-02 Last updated: 2017-06-26Bibliographically approved
3. The influence of system boundaries and baseline in climate impact assessment of forest products
Open this publication in new window or tab >>The influence of system boundaries and baseline in climate impact assessment of forest products
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Purpose

This article aims to explore how different assumptions about system boundaries and setting of baselines for forest growth affect the outcome of climate impact assessments of forest products during life cycle assessment (LCA), including potential climate impact mitigation from replacing non-forest benchmarks. This article attempts to explore how several assumptions interact and influence results for different products with different service life lengths.

Methods

Four products made from forest biomass were analysed and compared to non-forest benchmarks using dynamic LCA with time horizons between 0 and 300 years. The studied products have different service lives: butanol automotive fuel (0 years), viscose textile fibres (2 years), a cross-laminated timber building structure (50 years) and methanol used to produce short-lived (0 years) and long-lived (20 years) products. Five calculation setups were tested featuring different assumptions about how to account for the carbon uptake during forest growth or regrowth. These assumptions relate to the timing of the uptake (before or after harvest), the spatial system boundaries (national, landscape and single stand approaches) and the land use baseline (zero baseline and natural regeneration).

Results and discussion

The implications of using different assumptions depend on the type of product. The choice of time horizon for dynamic LCA and the timing of forest carbon uptake are important for all products, especially long-lived ones where end-of-life biogenic emissions take place in the relatively distant future. The choice of time horizon is less influential when using landscape or national spatial boundaries than when using a stand approach, but has great influence on the results for long-lived products. The influence of the methodological choices studied in the comparison of the products with their benchmarks has divergent outcomes. Short-lived products perform worse than their benchmarks with short time horizons whatever spatial boundaries are chosen, while long-lived products outperform their benchmarks with all methods tested.

Conclusions

The choices of spatial boundaries, temporal boundaries and land use baseline have a large influence on the results, but this influence decreases for longer time horizons. Short-lived products are more sensitive to the choice of time horizon than long-lived products. Recommendations are given for LCA practitioners: to be aware of the influence of method choice when carrying out studies, to prioritise case-specific data for forest growth and to communicate clearly how results should be used and interpreted.

National Category
Environmental Engineering
Research subject
Industrial Ecology
Identifiers
urn:nbn:se:kth:diva-207142 (URN)
Funder
Swedish Energy Agency
Note

QC 20170602

Available from: 2017-05-17 Created: 2017-05-17 Last updated: 2017-06-02Bibliographically approved
4. Climate impacts from road bridges: effects of introducing concrete carbonation and biogenic carbon storage in wood
Open this publication in new window or tab >>Climate impacts from road bridges: effects of introducing concrete carbonation and biogenic carbon storage in wood
2017 (English)In: Structure and Infrastructure Engineering, ISSN 1573-2479, E-ISSN 1744-8980Article in journal (Refereed) Published
Abstract [en]

The construction sector faces the challenge of mitigating climate change with urgency. Life cycle assessment(LCA), a widely used tool to assess the climate impacts of buildings, is seldom used for bridges. Materialspecificphenomena such as concrete carbonation and biogenic carbon storage are usually unaccountedfor when assessing the climate impacts from infrastructure. The purpose of this article is to explore theeffects these phenomena could have on climate impact assessment of road bridges and comparisonsbetween bridge designs. For this, a case study is used of two functionally equivalent design alternativesfor a small road bridge in Sweden. Dynamic LCA is used to calculate the effects of biogenic carbon storage,while the Lagerblad method and literature values are used to estimate concrete carbonation. The resultsshow that the climate impact of the bridge is influenced by both phenomena, and that the gap betweenthe impacts from both designs increases if the phenomena are accounted for. The outcome is influencedby the time occurrence assumed for the forest carbon uptake and the end-of-life scenario for the concrete.An equilibrium or 50/50 approach for accounting for the forest carbon uptake is proposed as a middlevalue compromise to handle this issue.

Place, publisher, year, edition, pages
Taylor & Francis Group, 2017
Keyword
Life cycles, wooden bridges, concrete bridges, environmental engineering, climate change, biogenic carbon storage, concrete carbonation
National Category
Environmental Engineering
Research subject
Industrial Ecology
Identifiers
urn:nbn:se:kth:diva-207128 (URN)10.1080/15732479.2017.1327545 (DOI)2-s2.0-85019192178 (Scopus ID)
Projects
EnWoBio - Engineered Wood and Biobased Building Materials Laboratory
Funder
Swedish Research Council Formas, 2014-172
Note

QC 20170602

Available from: 2017-05-16 Created: 2017-05-16 Last updated: 2017-06-02Bibliographically approved
5. Future scenarios for climate change mitigation of new building construction in Sweden: Effects of different technological pathways
Open this publication in new window or tab >>Future scenarios for climate change mitigation of new building construction in Sweden: Effects of different technological pathways
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Climate mitigation strategies are required with urgency. The Swedish construction sector contributes to a significant share of the country’s yearly greenhouse gas (GHG) emissions. A variety of alternative climate mitigation strategies is available aimed to different processes and activities related to production and operation of buildings. Several studies evaluating the effectiveness of these strategies have been performed at the building stock level. These studies however do not consider the technological change in manufacturing of building materials. The objective of this study is to evaluate the climate change mitigation effects of increasing the use of biobased materials in the construction of new residential buildings in Sweden under different scenarios related to technological change in material manufacturing. For this, the climate impact from Swedish new buildings has been assessed for the coming one hundred years using a model that combines scenario analysis based on official statistics and life cycle assessment of seven different building typologies. Eight different scenarios for increased use of low-impact building typologies such as timber buildings and low-impact concrete are explored under different pathways for growth of their market share and changes in energy production. The results show that the benefits from an increased use of biobased materials are significant in all scenarios evaluated, but decrease if the use of low-impact concrete expands more rapidly or under optimistic scenarios for energy production. Results are also highly sensitive to the choice of climate impact metric. Results also show that the Swedish construction sector can only reach maximum climate change mitigation scenarios if all the low-impact typologies are implemented together and rapidly, including a rapid switch to cleaner energy.

National Category
Environmental Engineering
Research subject
Industrial Ecology
Identifiers
urn:nbn:se:kth:diva-207143 (URN)
Projects
EnWoBio - Engineered Wood and Biobased Building Materials Laboratory
Funder
Swedish Research Council Formas, 2014-172
Note

QC 20170602

Available from: 2017-05-17 Created: 2017-05-17 Last updated: 2017-06-02Bibliographically approved

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