https://doi.org/10.14311/APP.2022.33.0585 Acta Polytechnica CTU Proceedings 33:585–590, 2022 © 2022 The Author(s). Licensed under a CC-BY 4.0 licence Published by the Czech Technical University in Prague ENVIRONMENTAL ASSESSMENT OF NON-METALLIC REINFORCEMENT FOR CONCRETE STRUCTURES AS AN ALTERNATIVE TO STEEL REINFORCEMENT Nadine Stoiber∗, Mathias Hammerl, Benjamin Kromoser Research Group for Resource-Efficient Structural Engineering, University of Natural Resources and Life Sciences Vienna, Peter-Jordan-Straße 82, 1190 Vienna, Austria ∗ corresponding author: nadine.stoiber@boku.ac.at Abstract. The concrete industry accounts for a significant amount of CO2 emissions worldwide. One ap- proach to counter this issue includes material reduction of structural components via the use of non- metallic reinforcement, such as carbon, glass and basalt fibre reinforced polymers. On the one hand, non-metallic reinforcement. However, as its environmental impact has not been sufficiently investi- gated yet, a Life Cycle Assessment of the production phase is presented within this paper. In a first step, the environmental impact of the sole various reinforcement components and types is compared to each other per mass, per tensile or rather yield strength as well as density unit, at which an envi- ronmental disadvantage of especially carbon-fibre reinforced polymers is apparent in most cases. In a further step, a focus is put on applying the environmental data of carbon-fibre reinforced polymers to a pedestrian bridge, which is finally compared to a conventionally reinforced concrete bridge and a steel bridge with similar boundary conditions. The latter results indicate that an adequate application of carbon-fibre reinforcement in structural components has the potential to lead to designs of less environmental impact in comparison to conventionally reinforced pendants. Keywords: Concrete structures, environmental impact, FRP reinforcement, life cycle assessment, non-metallic reinforcement. 1. Introduction: ’Concrete footprint’ According to [1], in 2018 the construction industry was responsible for approximately 10% of CO2 emis- sions worldwide. On a global level, the report further identifies concrete as most widely used building ma- terial type. What is more, it is predicted by [2] that the building material concrete will account for around 12% of worldwide greenhouse gas emissions in 2060. Besides emissions regarding the production phase and respective required fuels, concrete is characterised by so-called process emissions due to its intrinsic chemi- cal reduction from calcium carbonate to calcium ox- ide, which represent around two thirds of total emis- sions [3]. These numbers outline the urgency as well as the potential of the concrete industry in pushing attempts to decrease its emission-intensity forward. Several options exist to counter the above outlined issue, at which three major approaches, according to [4], are briefly listed: Reducing the amount of ce- ment via an optimization of the concrete mixture, a reduction of concrete material used via a struc- tural optimization of the design as well as the use of high-strength materials such as ultra-high perfor- mance concrete (UHPC) and fibre-reinforced poly- mers (FRP) made out of basalt, glass or carbon fibres. The latter approach is pursued within this paper, at which the environmental performance is subject of investigation. Firstly, the method and materials are outlined. Secondly, the investigated reinforcement types are compared with each other, solely on material level. Here, several matrix as well as fibre types are anal- ysed. Subsequently, the application of the environ- mental data of carbon fibre-reinforced polymers to pedestrian bridges as conducted in [5] is presented. 2. Methodology: Life Cycle Assessment According to EN ISO 14050, Life Cycle Assessment (LCA) is described as an assessment of the inputs, outputs and the potential environmental impacts of a product system throughout its life cycle. LCA is divided into several phases, including Life Cycle In- ventory (LCI) analysis, where the inputs and outputs of a product system are determined, as well as Life Impact Assessment Analysis (LCIA), where the envi- ronmental impacts of a product system are evaluated and assessed. Several characterisation models exist regarding the latter step of an LCA, at which CML- IA from the University Leiden is mentioned within this context [6]. The underlying standardisation of conducting an LCA comprises EN ISO 14040 (fundamentals) and EN ISO 14044 (instructions). EN ISO 14025 outlines the use of Life Cycle Assessment to establish an Envi- 585 https://doi.org/10.14311/APP.2022.33.0585 https://creativecommons.org/licenses/by/4.0/ https://www.cvut.cz/en J. Anderson, M. Hammerl, B. Kromoser Acta Polytechnica CTU Proceedings Figure 1. Comparison of GWP values extracted from EPDs with the European average of [7]. ronmental Product Declaration (EPD). The national standard ÖNORM EN 15804 has to be highlighted in this context, which regulates the development of EPDs for the product category of construction prod- ucts. Life cycle phases of a product system range from product, construction process to the end of life stage. The product stage is compulsory to be cov- ered when developing an EPD, at which this stage is divided into three categories: Raw material supply (A1), transport (A2) and manufacturing (A3). This type of LCA is described as cradle-to-gate. Com- monly, a cradle-to-gate LCA represents the most ad- equate type, as the inputs and outputs are often char- acterised by satisfying data completeness and quality. Other life cycle stages, such as the construction pro- cess stage, are accompanied by comparatively more underlying assumptions. At best, all life cycle stages are covered within an EPD. Due to limited data avail- ability, the production stage of the considered con- struction products is assessed within this paper. Fur- thermore, several impact indicators are selected to be evaluated, such as the Global Warming Poten- tial (GWP) in kg CO2-eq., the Acidification Potential (AP) in kg SO2-eq. as well as the Abiotic Deletion Potential of fossil fuels (ADPf) in MJ. Commonly, due to public popularity, the GWP is paid the most attention to. In order to establish a wider picture of the environmental impact of the considered products, further impact indicators should be assessed. Consulted sources within this paper include EPDs and Life Cycle Inventory data. Details about the respective sources as well as the chosen declared or rather functional units are outlined in the sections be- low. It is crucial to note that irregularities go hand in hand with the comparison of environmental data from varying sources. For example, the LCIA phase of the Life Cycle Assessment can be based on varying characterisation models. The authors aimed at main- taining maximum transparency within the process to enable traceability and reproducibility. 2.1. Excursion: Data bias To briefly outline the phenomenon of data bias and raise awareness regarding data quality within Life Cy- cle Assessment, the example of steel reinforcement is consulted. Extracted GWP values of steel reinforce- ment (cradle-to-gate LCA, declared unit: 1 kg) as done by [5] are illustrated in Figure 1. The first five, grey bars represent extracted GWP values from Eu- ropean EPDs, at which the last, green bar outlines the European average of steel production in 2019 pro- vided by [7]. For further detailed information on data sources of the EPDs, the reader is directly referred to [5]. Given the GWP values extracted from the EPDs in Figure 1, one would assume to have an av- erage value of around 1.0 kg CO2-eq., nevertheless, the European average is higher. When analysing the manufacturing methods of the various EPDs it be- comes apparent that, except for Ukraine, all EPDs are built up on electric arc furnace. Nevertheless, [8] shows otherwise, at which not electric arc furnace but basic oxygen steelmaking represents the major man- ufacturing method of steel products in Europe. The average of the given data extracted from the EPDs is therefore not representative for the Global Warming Potential of steel reinforcement in Europe. 3. Results on material level: Comparison of reinforcement components and types Figure 2 and Figure 3 show the normalized results of the GWP of various fibre and matrix types. GWP values for carbon fibres are extracted from [9], for glass fibres from [10], for basalt fibres from [11], for styrene butadiene rubber and acrylate from [12], for polyester resin, vinylester resin and epoxy resin from [13] as well as from [14]. Impact indicators, like the GWP, were directly extracted from these sources. Only the last source, [14], represents LCI data, which was extracted and subjected to self- evaluation according to the specifications of ÖNORM EN 15804:2020. In all cases, the production stage (cradle-to-gate) was considered. Regarding Figure 3 it is apparent that carbon fi- bres are characterised by the highest Global Warm- ing Potential in comparison to glass and basalt fi- bres. As reason the energy-intense production pro- cess up to 3,000řC is mentioned. The differences be- tween the various matrix materials in Figure 2 are not that significant, nevertheless, a row in depen- dence of the GWP is possible. The normalized GWP values of carbon fibre-reinforced polymers (CFRP), glass fibre-reinforced polymers (GFRP) and basalt fibre-reinforced polymers (BFRP) are illustrated in Figure 4, at which epoxy resin was chosen as matrix material. The results are presented in a normalized 586 vol. 33/2022 Non-Metallic Reinforcement for Concrete Structures Figure 2. Comparison of the GWP of different matrix materials (normalized values). Figure 3. Comparison of the GWP of different fibre types (normalized values). Figure 4. Comparison of the GWP of different FRPs (normalized values). manner to enhance readability. The respective com- ponents of the FRPs were combined according to an analysis of data sheets, at which the respective fibre share ranges from 75 to 90% and the matrix mate- rial share ranges from 10 to 25%. The GWP of car- bon fibres of 26.4 kg CO2-eq. per kg was extracted from [9] and is given as example. Comparing Figure 3 with Figure 4 it can be seen that the trend of car- bon being the least favourable material choice in case of environmental impact continues, nevertheless the difference between the varying fibre types becomes smaller. In this context, the study of [15] is men- tioned, who conducted a cradle-to-grave LCA for con- ventional steel- and textile-reinforced (glass, carbon and basalt) façade elements. Their findings indicate that all textile versions show comparatively less en- vironmental impact. The carbon version showed a comparatively higher impact than the glass or basalt solution amongst most of the investigated impact in- dicators (GWP, AP and Eutrophication Potential). 3.1. In detail: CFRP reinforcement The environmental impact of CFRP is further inves- tigated based on evaluations done in [5], at which the analysis is extended to impact indicators such as the Acidification Potential in kg SO2-eq. (AP) and the Abiotic Depletion Potential of fossil fuels in MJ (ADPf). Furthermore, the environmental impact of CFRP reinforcement is directly compared to the one of conventional steel reinforcement (European aver- age, compare with Figure 1). The results are illus- trated in Figure 5 to Figure 7. The properties of a CFRP rebar product from solidian GmbH are con- sulted [16]. In Figure 5, the results are solely based on masses or rather per declared unit of 1 kg of the product sys- tem. This figure shows the environmental advantage of conventional steel reinforcement in comparison to CFRP reinforcement amongst all considered impact indicators. Figure 6, which is based on masses as well as on the performance of the reinforcement type, still shows environmental benefits of steel reinforcement. Nev- ertheless, an additional consideration of the perfor- mance, more precisely the tensile strength of 2,100 MPa of CFRP reinforcement as well as the yield strength of 550 MPa of steel reinforcement shows re- sults more on favour of CFRP reinforcement than a sole consideration of the masses as illustrated in Fig- ure 5. Figure 7 shows otherwise, at which an environmen- tal benefit of CFRP reinforcement amongst the im- pact indicators GWP and ADPf is visible. Here, the performance (tensile and yield strength) as well as the related densities (7,850 kg/m3 for steel reinforcement, 1,500 kg/m3 for CFRP reinforcement) were consid- ered. Figure 7 already shows the potential of CFRP reinforcement as an environmentally friendly alterna- tive to steel reinforcement on the material level. 587 J. Anderson, M. Hammerl, B. Kromoser Acta Polytechnica CTU Proceedings Figure 5. Comparison of steel and CFRP reinforce- ment per kg product system (normalized values). Figure 6. Comparison of steel and CFRP reinforce- ment per kg product system as well as per MPa tensile respectively yield strength (normalized values). 4. Results on system level: Comparison of pedestrian bridges The environmental data of CFRP were further ap- plied to pedestrian bridges of varying building types by [5], whose results will be outlined as a subsequent step. The consulted bridges are illustrated in Fig- ure 8. The first bridge is a carbon concrete bridge in Albstadt Ebingen, Germany and was built in 2015 (abbreviated with B1-CCB), which is characterised by a thin CFRP reinforced cross section and a gal- vanized steel railing. The second bridge is a conven- tional steel reinforced concrete bridge, built in 2009 in Vienna, Austria (abbreviated with B2-RCB). The last bridge, a mild steel bridge, was built in 1999 in Vienna, Austria (abbreviated with B3-SB). The masses for the quantity survey were extracted from [17] for B1-CCB and provided by the Municipal De- partment 29 in Vienna Austria in case of B2-RCB and B3-SB. Further details can be found in [5]. The func- tional unit for the subsequent comparison is a pedes- trian bridge with a span length of ∼ 15 m, an effective width of ∼ 3 m and an imposed load of ∼ 5 kN/m2. The materials of the superstructure were considered. The results of the environmental assessment of the pedestrian bridge types are illustrated in Figure 9. The impact indicators GWP and ADPf are clearly in favour of the CFRP reinforced concrete bridge due to Figure 7. Comparison of steel and CFRP reinforce- ment per MPa tensile respectively yield strength as well as per density unit (normalized values). significant savings in material masses when compar- ing B1-CCB with B2-RCB. To get a deeper understanding of the allocation of the environmental impacts, the results are fur- thermore divided per building material and outlined in Figure 10 to Figure 12. The consideration of the GWP as well as of the ADPf shows that the galva- nized steel railing of B1-CCB has a significant share in the whole environmental impact. Regarding ADPf, the reinforcement is responsible for the majority of the environmental impact. Regarding AP in Fig- ure 11, it becomes apparent that the CFRP reinforce- ment is mainly responsible. The environmental data are characterised by high limits of variation, at which [9] gives the consultation of different reaction equa- tions for the combustion of ammonia and hydrocyanic acid during the production process of carbon fibres as reason for these variabilities. This circumstance outlines room for higher data precision regarding the AP in the future. Furthermore, the authors want to indicate, that a more comprehensive consideration of the environmental impact was initially intended, with further impact indicators such as Ozone Depletion Potential (ODP), Eutrophication Potential (EP) and Photochemical Oxidant Creation (POCP) being con- sidered. Unfortunately, the respective environmental data of CFRP were either not available nor valid. Up- dates in the data availability are constantly checked and re-evaluated by the authors. 5. Conclusion The intention of this paper was to evaluate, whether fibre-reinforced polymers are a possible environmen- tally friendly alternative to conventional steel rein- forcement in concrete structures or not. In a first step, the varying fibre and matrix material types were solely evaluated per unit weight, at which car- bon fibres and CFRP reinforcement showed by far the highest Global Warming Potential. Subsequently, a more detailed environmental assessment of CFRP re- inforcement on material level showed that steel rein- forcement is more favourable when considering solely the declared unit of 1 kg as well as the declared unit 588 vol. 33/2022 Non-Metallic Reinforcement for Concrete Structures Figure 8. Pedestrian bridge examples, from top to bottom: B1-CCB (solidian GmbH), B2-RCB and B3-SB (Mathias Hammerl). Figure 9. Comparison of impact indicators of vari- ous pedestrian bridge types (normalized values), ex- tracted from [5]. Figure 10. Comparison of the GWP of various pedestrian bridge types (normalized values) divided by the used building materials, extracted from [5]. Figure 11. Comparison of the AP of various pedes- trian bridge types (normalized values) divided by the used building materials, extracted from [5]. Figure 12. Comparison of the ADPf of various pedestrian bridge types (normalized values) divided by the used building materials, extracted from [5]. 589 J. Anderson, M. Hammerl, B. Kromoser Acta Polytechnica CTU Proceedings in combination with the tensile or rather the yield strength of the respective material. Nevertheless, the consideration of the reinforcements’ performance as well as the density of the material showed a lesser en- vironmental impact of CFRP reinforcement in com- parison with conventional steel reinforcement. In a second step, an assessment and comparison of the su- perstructure of a carbon concrete, a reinforced con- crete and a mild steel pedestrian bridge outlined the environmental benefits of the carbon concrete bridge type. The potential of CFRP as an environmentally friendly alternative to steel reinforcement in the case of pedestrian bridges could be shown. It has to be mentioned that overall conclusions of this applica- tion example to other structures are not acceptable: An individual profound analysis is always necessary. Furthermore, only the production stage of the rein- forcement components and pedestrian bridge mate- rials was considered. A more holistic consideration of further life cycle stages with an extension to other structural components is highly recommended as an optimal continuation of this study. Acknowledgements The authors would like to thank Dirk Neuburg from the Municipal Department 29 in Vienna and Dr. Sergej Rem- pel from solidian GmbH for the provision of the orig- inal bridge documents and additional information used for the bridge examples. They would like to thank Clare Broadbent from the World Steel Association for the pro- vision of environmental data as used within the cradle-to- gate LCA. The authors also want to thank Dr. Andrea Hohmann for her support in the early stage of the as- sessment. A part of the data collection was done within the scope of the VIF project 2019 "Potentiale von nicht- metallischer Bewehrung im Infrastruktur-Betonbau". The authors want to thank the customers Austrian Railways (ÖBB), the Austrian Autobahn and highway financing stock corporation (Asfinag), the Bundesministerium für Klimaschutz, Umwelt, Energie, Mobilität, Innovation und Technologie (BMK) as well as the Austrian Research Pro- motion Agency (FFG) for the management. References [1] International Energy Agency and the United Nations Environment Programme. 2018 Global Status Report: towards a zero-emission, efficient and resilient buildings and construction sector, 2018. https: //wedocs.unep.org/handle/20.500.11822/27140. [2] OECD. Global Material Resources Outlook to 2060: Economic Drivers and Environmental Consequences (Paris: OECD Publishing), 2019. https: //www.oecd.org/environment/waste/highlights-glo bal-material-resources-outlook-to-2060.pdf. [3] G. Mauschitz.Emissionen aus Anlagen der Österreichischen Zementindustrie, 2018. [4] B. Kromoser, P. Preinstorfer, J. Kollegger. 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