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Glass Struct. Eng. https://doi.org/10.1007/s40940-022-00211-y RESEARCH PAPER Make or break the loop: a cross-practitioners review of glass circularity Esther Geboes · Waldo Galle · Niels De Temmerman Received: 1 June 2022 / Accepted: 4 November 2022 © The Author(s) 2022 Abstract End-of-life insulating glass units (IGUs) to be the main opportunities for glass circularity. The continue to follow a linear, wasteful path from reno- cross-practitioners’ insights in this paper contribute to vation and demolition sites into landﬁlls or low-value close the glass loop and to further development and recycling. To get one step closer to the question of how up-scaling of circular strategies. to close the glass loop, this exploratory research out- lines a cross-practitioners review of glass circularity in Keywords Insulating glass unit · Circular economy · conventional Flemish and Brussels practices. A series Waste management · Circular valorisation strategies · of semi-structured interviews with network actors and Closed material loops · Barriers · Opportunities an extensive literature study is conducted to identify existing and missing circular practices and to pinpoint the key barriers and opportunities. In general, the cir- cular strategies repurpose and open-loop recycling of 1 Introduction end-of-life IGUs are successfully applied in Flemish and Brussels construction practices. Repair, reuse, and In the Belgian region of Flanders, like in other Euro- closed-loop recycling remain unexplored. The main pean regions, policy is shifting from waste to sustain- barriers are the lack of collaboration, logistic and labour able materials management by establishing an econ- costs to collect end-of-life IGUs, its complex disassem- omy of closed material loops by 2025 (European Com- bly, the lack of legal incentives and the conservative- mission 2020; Galle et al. 2017;OVAM 2014). The ness of the construction sector. Case studies, the high construction sector plays a crucial role in the reali- recycling potential and the scale of projects are found sation of those ambitions due to its material intensity and its potential to use recycled materials. In Europe, E. Geboes ( ) · W. Galle · N. De Temmerman this sector is responsible for 20 to 30% of the total Department of Architectural Engineering, Vrije mass of generated waste (Ellen MacArthur Foundation, Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium e-mail: Esther.Geboes@vub.be McKinsey Center for Business and Environment, and SUN 2015). Whereas most stone and concrete waste W. Galle are already being recycled for various applications, still e-mail: Waldo.Galle@vub.be 54% of the construction and demolition waste is sent N. De Temmerman to landﬁlls (Ibid.). In Flanders and Brussels-Capital e-mail: Niels.De.Temmerman@vub.be Region (BCR), these landﬁlled materials mainly relate W. Galle to waste fractions of wood, PVC, plasterboard, insu- VITO Transition Platform, Flemish Institute for Technological Research (VITO), Boeretang 200, 2400 Mol, Belgium lation materials such as glass wool, and ﬂat glass 123 E. Geboes et al. (Debacker et al. 2021;OVAM 2014; Romnée and Vri- “the energy intensity of glass production is estimated jders 2018). Architectural ﬂat glass, for instance, is to be around 7–8 GJ/t. This is less than other energy a fully recyclable material and yet, it follows a lin- industries such as steel, 20–30 GJ/t and aluminium, ear, wasteful path from renovation and demolition sites 90–100 GJ/t, but more than cement, 3–6 GJ/t.” It con- into landﬁlls or low-value recycling (Debacker et al. tributes to signiﬁcant global CO emissions, contribut- 2021; DeBrincat and Babic 2018; Hestin et al. 2016; ing to annual CO emissions of approximately 86 Mt Westbroek et al. 2021). In Flanders and BCR, it is it (Westbroek et al. 2021). Moreover, raw materials are is typically crushed together with other building rub- running out: roughly 32 billion to 50 billion tonnes of ble. This mixed waste is then either brought to the suitable sand are depleted globally each year, mainly incinerator, put into landﬁlls, or used as an impurity for making concrete, glass, and electronics (Bendixen in recycled aggregates for low-value applications such et al. 2019). By 2050, this demand could outstrip the as concrete for pavements, foundations, or road con- supply (Ibid.). structions (Debacker et al. 2021; DeBrincat and Babic 2018; Dubois et al. 2013; Glass for Europe 2013;Hes- tin et al. 2016; Nodehi and Mohamad Taghvaee 2022). 1.1 The circular economy as an alternative model In 2007, the global ﬂat glass production reached 44 million tonnes, of which 70%—or almost 31 mil- Conventionally, the construction industry adopts a lin- lion tonnes—was architectural ﬂat glass (Hubert 2019). ear take-make-waste model (Romnée and Vrijders Architectural ﬂat glass implies the glazing used in 2018). In this linear economy, all investments end up as buildings and structures, such as insulated glazing, inte- waste one day. The circular economy is an alternative rior glazing, etc. (Belis et al. 2019). A commonly used model that strives for an economy without waste by insulated glazing in the building envelope is the insu- keeping materials in circulation for as long as possible lating glass unit (IGU), a unit composed of two or (Ibid.) For instance, by implementing circular strate- more glass panes separated by a space bar that is glued gies such as repairing, reusing, repurposing, and recy- with a sealant (Ibid.). The development of the IGU has cling ﬂat glass, the material loop is closed and conse- been driven by reducing the operational energy need for quently, waste is minimised (Ellen MacArthur Foun- heating and cooling buildings while optimizing the use dation et al. 2015). of daylight (Glass for Europe, 2012). As a result, the In theory, glass is a 100% recyclable material. Con- importance of ﬂat glass has been growing in both new cretely, this means that IGUs can be processed into ﬂat buildings and renovations. Replacing outdated glazing glass cullet—or in other words, crushed and processed with new two-layer or three-layer IGUs has become ﬂat glass—and can then be reintroduced in the pro- a standard intervention to meet energy requirements. duction process to produce new ﬂat glass products or Yet, these interventions have led to an almost expo- other glass products. The ﬁrst is also known as closed- nential increase in the consumption of glass material loop recycling, deﬁned by Debacker et al (2021)as“the per window (Lendager and Pedersen 2020). For Flan- material is recycled and used in the same application ders, as well as for other European regions, a signiﬁ- without changing the original properties of the recycled cant increase in both ﬂat glass consumption and waste material”. However, the ﬂat glass used for recycling is expected. To illustrate, Dubois et al. (2013) estimate must be free of contamination (e.g., ceramics, stones that 127 to 151 kt of ﬂat glass waste was generated in and porcelain (CSP), glass ceramics, metals, organic Flanders in 2011. Four years later, in 2015, this amount substances, and hazards) that might originate from IGU was increased to 172 kt according to Debacker et al. components (e.g., metal spacer bar) or other building (2021). materials (concrete, bricks, steel, etc.) on the demoli- To meet the current and future demand, more ﬂat tion or renovation site. As DeBrincat et al. (2018) warn: glass needs to be manufactured. However, manufactur- “Once introduced into a furnace contamination can take ing ﬂat glass—the ﬂoat process—is an energy-intensive several days to pass through the system. Thus low lev- process in which primary raw materials, principally els of contamination can result in several days of lost silica sand, soda, lime, and dolomite, are melted at production which will cancel out the environmental and high temperatures between 1500 and 1600 °C (Souvi- cost beneﬁts of recycling.” The second, open-loop recy- ron and Khan 2021). Westbroek et al. (2021) compare: cling, implies that ﬂat glass cullet is used to produce 123 Make or break the loop: a cross-practitioners review of glass other glass products, such as container glass, glass wool tomorrow’s architectural ﬂat glass waste in a sustain- insulation, and foam glass. Recycling, therefore, elim- able manner. inates the need for more and more raw materials. How- ever, important to notice is that once ﬂat glass is open- loop recycled into container glass, which implies it is 2 Research objectives and scope mixed with container glass cullet, it can never be recy- cled back into ﬂat glass. This is due to certain impurities In the last few years, main barriers and opportunities of that may be present in bottles and jars and do not meet circular strategies have been studied extensively for the building sector. Some papers focus on the entire build- the high-quality requirements of ﬂat glass production (Rodriguez Vieitez et al., 2012). For instance, metal ing sector (Giorgi et al. 2020; Harder, 2018), while oth- ers narrow it down to materials and systems (Hobbs and contamination in bottles originate from cans or caps that are thrown in the waste collection banks (Ibid.) Adams 2017; Hartwell et al. 2021). Yet, none of them The same logic applies to applications like glass wool covers the circular strategies and practices related to the or foam glass. These contaminants may cause damage management of end-of-life IGUs. Therefore, this work to the produced glass, as well as to the furnace (Dubois addresses three, so far unanswered, research questions: et al. 2013; Hubert 2019). For instance, CSP and glass � What is the present level of application of circular ceramics have a higher melting point than glass com- valorisation strategies, not only recycling, but also ponents and might not melt with the glass. As a result, reuse, repair, and repurpose, for IGUs in Flanders defects may occur in the ﬁnal glass product, in partic- and Brussels? ular aesthetic and technical quality losses (Debacker � Which circular valorisation strategies for IGUs are et al. 2021). still missing in Flemish and Brussels’ practices and Additionally, the use of cullet has many environ- what does this mean locally and globally? mental beneﬁts. First, for every tonne of cullet used � What are the related barriers and opportunities for in the manufacturing process, 1.2 tonnes of primary end-of-life IGUs? raw materials are saved (DeBrincat and Babic 2018; Lebullenger and Mear 2019). Second, compared to the To answer these questions, we must look beyond energy needed to convert primary raw materials into the technical properties of glass and glass production glass, less energy is needed to melt the glass cullet. theory. Like all sustainability transitions, a shift from a Consequently, the furnace temperature can be lowered. linear to a closed-loop economy requires to change day- In general, every 10% glass cullet added to the melting to-day practices as well as underlying values (Geels process reduces the energy consumption by approx- et al. 2011). Those practices and values also explain imately 3% (Dubois et al. 2013; Hestin et al. 2016; why making the transition is so difﬁcult. To get one Lebullenger and Mear 2019; Westbroek et al. 2021). step closer to the question of how to close the glass Summarised, replacing all primary raw materials with loop, this article creates on the one hand a complete and glass cullet would result in about 30% furnace energy thorough overview of the current linear waste manage- savings. At present, however, only a third of the batch ment practices for end-of-life ﬂat glass in Flanders and consists of secondary raw materials, being the internal BCR. On the other hand, this study discovers which production waste (e.g., cutting losses, melting losses) innovative, inspirational circular strategies are already of the ﬂat glass manufacturers and processors (Butler implemented in the regions and which are still miss- and Hooper 2019). ing in today’s practices compared to other regions. In Altogether, the case for recycling ﬂat glass is strong. total, four circular valorisation strategies within ﬂat Yet only 11% of ﬂat glass is recycled worldwide glass management—namely, repair, reuse, repurpose, (Harder 2018), while other circular strategies, like the and recycle—and the related barriers and opportunities repair, reuse, or repurpose of IGUs, remains a niche are studied in more detail. practice. Taking into account the signiﬁcant growth in The focus of this article is set on Flemish and both ﬂat glass consumption and waste generation, and BCR. Both regions are forerunners in applying cir- the potential savings of energy, raw materials and CO cular strategies in the construction sector. Initiatives emissions of a closed material loop for ﬂat glass, urgent such as Circular Flanders or Brussels-Capital Regional questions arise about how we will manage today’s and Program for a Circular Economy (BCRPCE) have 123 E. Geboes et al. proved to be successful in practice so far. Introduced while IGU refers to the system of assembly whereby in 2011, the Flanders Materials Programme “provides two or more glass panes are separated by a spacer bar Flanders for a future-proof economy where material and a cavity ﬁlled with insulating gas. The study has cycles are closed”, building on three pillars: a long-term a speciﬁc focus on the IGU, and more speciﬁcally on vision, policy-relevant scientiﬁc research and actions the glass of this product. The other components—the and projects in the ﬁeld (Ellen MacArthur Founda- spacer bar, coatings or ﬁlms, and the seals—are not tion 2016). Furthermore, the regions Flanders and BCR considered. host 17 insulating glazing manufacturers (members of Verbond van de Glasindustrie VGI) (Verbond van de Glasindustrie 2019) and two ﬂat glass recyclers. 3 Method The regions play an important role in the interna- tional sustainable management of today’s end-of-life 3.1 Data gathering ﬂat glass, especially for the export and import of recy- cled ﬂat glass (cullet). Almost half of the recycled ﬂat First, to create a representative, general overview of the glass in Flanders—123 tonnes out of 295 tonnes—was ﬂat glass management practices in Flanders and Brus- imported from neighbouring regions in 2015 (Debacker sels, literature material was selected based on three cri- et al. 2021). teria. The ﬁrst selection criterium was “relevant for the With the insights of this exploratory research, it is Flemish and Brussels building sector”, which relates to possible to explore under which conditions the circu- the location context of this study. For instance, several lar practices can be replicated and upscaled in Flanders included papers conducted a material ﬂow analysis at a and BCR; but also, which other niche practices (from global scale (Butler and Hooper 2019; Westbroek et al. abroad) could ﬁnd ground in the Flemish and Brus- 2021), at European scale (Hestin et al. 2016) and at a sels region. Although the article focuses on the prac- local scale (Debacker et al. 2021; Dubois et al. 2013). tices in Flanders and BCR, the insights are presented The second selection criterium was “circular valorisa- in this paper as a basis to further question construction tion strategies for ﬂat glass”. Included papers focus on practices in other regions in Europe and beyond. For speciﬁc circular alternatives like closed-loop recycling example, inspirational circular practices and the related (DeBrincat et al. 2018; DeBrincat and Babic 2018; barriers and opportunities might be of interest to other Glass for Europe 2013; Rodriguez Vieitez et al., 2012; regions with similar climate and material scarcity chal- Wittekoek 2020), repair practices (Mohamed 2020; lenges. Souviron 2021), and reuse practices (Gorgolewski First, section two (cf. 2) explains how the studies 2008; Hartwell et al. 2021), and/or highlight pioneer- and interviewees were selected (cf. 2.1) and how the ing projects (Jackson and Lanzarotto 2021;Bowers data was analysed (cf. 2.2). Then, in section three (cf. and King 2013). The third and last selection criterium 3) the key results of the reviewed papers, reports and was “recent, up-to-date research and products”. Conse- interviews are highlighted. An overview is given of the quently, the selected papers and reports were published conventional practices—quantities of waste, origin and in 1999 or later. The limit of 1999 relates to the intro- collection of waste, and their application—for both pre- duction of the EU Landﬁll Directive in 1999. It intro- and post-consumer ﬂat glass waste (cf. 3.1). Then, the duced stringent technical requirements that resulted in encountered circular practices for managing pre- and a signiﬁcant reduction in the amount of waste ending up post-consumer glass are discussed and missing circular in landﬁlls. Furthermore, Hartwell and Overend (2020) practices are identiﬁed (cf. 3.2). Next, section four (cf. illustrate “that at 25 years, it would be expected that at 4) discusses, per theme, the barriers that hinder these least 86% of IGU units would fail to meet their initial circular practices, as well as the opportunities that are functional performance requirements”. created. Last, a conclusion and further research possi- Second, interviews are conducted with experts in bilities are given (cf. 5). circularity and with network actors active in circular Throughout this paper, the terms insulated glaz- practices of ﬂat glass management in Flanders and ing and insulating glass unit are used interchangeably. BCR. The aim of the interviews is to collect the quali- Insulated glazing refers to a more overarching term, tative experiences of the actors and their practices and e.g., vacuum glass unit and insulating glass unit (IGU), to obtain a thorough understanding of the main barriers 123 Make or break the loop: a cross-practitioners review of glass and opportunities they encounter when implementing themes: organisation, (material-) technical aspects, leg- circular strategies for ﬂat glass. The interviews were islation, ﬁnancial aspects, and mentality and knowl- semi-structured, with a common set of predetermined edge. The results were then compared to create a com- questions focussing on: prehensive understanding of the key barriers and oppor- tunities encountered. � The role and responsibility of the interviewees in the ﬂat glass supply chain; � The existing (non-)circular operations, processes, 4 Management of end-of-life IGUs in Flanders and interactions of the interviewees in the supply and BCR chain; � And the experience of the interviewees with the Mohamed (2020) points out that IGUs are mainly being implementation of circular valorisation strategies replaced due to failure of the assembly (e.g., seal fail- (e.g., barriers and opportunities). ure) even though the technical life of the glass sheets The interviews took place between November 2019 themselves has not been reached. Due to the degrada- and October 2021 and each interview lasted 45 to tion of the primary seal, the insulating gas in between 60 min. the glass sheets can escape and external air can enter An overview of the major network actors of the cur- the cavity. This results in a signiﬁcant drop in thermal rent ﬂat glass supply chain (for the IGU speciﬁcally) performance of the IGU and it might lead to condensa- and the material and intangible ﬂow between them is tion issues between the glass panes, lowering the trans- mapped in Fig. 1. From these major actors, only the parency of the window (Ibid.). Hartwell and Overend network actors with experience in implementing circu- (2020) mention a predicted service life of only 25 years lar practices are targeted: three ﬂat glass or insulated for IGUs. glazing manufacturers active in glass recycling, three In general, the end-of-life IGU can be categorized glass recyclers or collectors for recycling, one architect into two types of glass waste: pre-consumer and post- with experience in glass recycling, two deconstruction consumer ﬂat glass waste. The former is “waste glass contractors with expertise in disassembly for reuse or resulting from the manufacturing of products that con- repurpose, and four researchers on glass sustainability. tain glass as one of their components, and which In total 13 network actors and researchers were inter- leaves the speciﬁc facility where it was generated, viewed. Ten of the targeted network actors are based becoming waste but not reaching the consumer mar- in Belgium and three in European countries outside ket” (Rodriguez Vieitez et al., 2012). Examples of pre- Belgium, namely France, the United Kingdom, and the consumer ﬂat glass waste are offcuts and pieces from Netherlands. defective manufacturing or surplus manufacturing. The latter is “waste glass originated after the use of the glass products at the consumer market”, for example from renovation, deconstruction, or demolition of a building 3.2 Analysis procedure (Ibid.). Besides, a distinction is made between internal and The data emerging from literature research and the external ﬂat glass waste, which indicates ownership of interviews was analysed through qualitative coding ﬂat glass waste by the ﬂat glass producer (internal) analysis, which consists of categorising data in themes or an external company, such as an independent insu- (i.e., coding), constant comparison and exploring the lated glazing manufacturer or contractor (Dubois et al. links between those themes. By comparing the results, 2013). Looking through the lens of construction prac- a comprehensive understanding of the key barriers and tices, the analysis below will show that this ownership opportunities could be created. An early estimate of is deciding for the further reapplication of the waste themes was set up based on the draft notes made dur- (cf. 3.1). ing the interviews. Then, the coding process was done manually by highlighting the data and linking them to the most appropriate theme. The themes were fur- ther adapted during this process. This resulted in ﬁve 123 E. Geboes et al. Fig. 1 Value Network Map of the current major network actors of the ﬂat glass sector showing the material and intangible ﬂows between them (mapping method after Galle and Matti (2022)) 4.1 Conventional practices: business-as-usual waste management 4.1.1 Pre-consumer ﬂat glass waste from IGUs Quantities per origin and application The Sankey diagram in Fig. 2, from a recent study conducted in the context of the Flemish Living Lab on circular construc- tion (Galle et al. 2019), shows that pre-consumer ﬂat glass waste—which amounted to 92 kt in 2015—fol- Fig. 2 Sankey diagram of the pre-consumer ﬂat glass ﬂow per lows a circular path into recycling and reuse. Most of origin, ownership, and application in Flanders, expressed in kilo- the pre-consumer ﬂat glass waste (57 kt)—consisting tonnes (reference year 2015). Results from and ﬁgure based on mainly of internal waste—is re-applied to high-value Debacker et al. (2021.) applications like closed-loop recycling (56 kt or 61%) or reuse (1 kt or 1%) (Ibid.). The other 35 kt (or 38%), mainly external pre-consumer waste, is open-loop recy- cled to other glass applications, e.g., container glass, glass ﬂows can be distinguished—based on how the glass wool insulation or foam glass (Ibid.). glass is collected and brought to the recycler—for the Collection and applications The interviews with recycling process: monolithic glass, laminated glass, recyclers and collectors show that four pre-consumer insulated glazing, and mixed glass. 123 Make or break the loop: a cross-practitioners review of glass The ﬁrst ﬂow, monolithic glass, refers mainly to the collected internal waste originating from the manufac- turing process (e.g., melting and cutting). This glass is unprocessed, i.e., without ﬁlms or spacers, and is also known as annealed glass. According to the interviewed recyclers and manufacturers, this ﬂow is typically rein- troduced as a secondary raw material to manufacture ﬂat glass. The second ﬂow refers to the collected laminated glass waste. This is mainly generated during the pro- cessing of annealed glass into laminated glass. Lam- Fig. 3 Schematic representation of the advanced and minimal inated glass is a type of safety glass that contains selective collection method for building materials a polyvinyl butyral (PVB) interlayer between two or more glass panes (DeBrincat and Babic 2018). After removing the PVB interlayer and separating the glass panes with a pre-treatment, the interviews with recy- 4.1.2 Post-consumer ﬂat glass waste from IGUs clers and manufacturers indicated that this ﬂow is gen- erally closed-loop recycled to ﬂat glass. Quantities per origin and application Debacker et al. The third ﬂow, insulated glazing, originates from estimate that approximately 80 kt of post-consumer order surpluses or damage during installation or trans- ﬂat glass waste was collected in 2015 in Flanders. port of the panes. The interviews with ﬂat glass recy- Approximately 22 kt through the advanced selective clers and manufacturers stress the importance of not deconstruction method, and 58 kt through the mini- damaging the spacer bars of the IGU during collection. mal selective deconstruction method. The ﬁrst method These spacers bars often contain metals, such as nickel implies the separate collection of wood, soil and stones, sulphide, that need to be removed carefully prior to mixed stone waste, mixed residual waste, rooﬁng, the recycling process (Debrincat et al. 2018). Nickel rigid plastics, plasterboard or gypsum, and glass waste sulphide inclusion can cause spontaneous breakage (Debacker et al. 2021), while the minimal selective of glass after manufacture and toughening processes deconstruction method only includes the separate col- (Kasper 2019). According to the interviewed recyclers, lection of four fractions: wood, soil and stones, the this contaminant cannot be detected with the current mixed stony fraction, and the mixed residual fraction infrastructure of the recycling plant. Consequently, the (Ibid.) (Fig. 3). interviewed ﬂat glass manufacturers are not willing to Only a small fraction, approximately 21 kt (27%) take the risk and do not accept this ﬂow for closed-loop of the collected post-consumer ﬂat glass in Flan- recycling. Instead, this ﬂow is typically open-loop recy- ders, is open-loop recycled to container glass (e.g., cled to container glass, glass wool insulation or foam jars, bottles, etc.), glass wool insulation or foam glass glass. (Debacker et al. 2021). The majority of post-consumer The last ﬂow refers to a combination of the ﬂat glass waste—which amounts to 59 kt (73%)– ends above-discussed collected ﬂows: laminated glass, non- up in low-value applications (Ibid.). Multiple studies laminated glass, insulated glazing, and depending on on a regional Flemish level (Dubois et al. 2013), and the case, sometimes mixed with other building materi- European level (DeBrincat and Babic 2018;Glass for als (e.g., other types of glass, stones) from the installa- Europe 2013; Hestin et al. 2016) conﬁrm that post- tion process. One interviewed recycler mentioned that consumer ﬂat glass waste is almost never recycled, with the current infrastructure at the recycling plants, reused or repaired. Instead, in Flanders, about 1 kt ends it is not technically or ﬁnancially feasible to separate up (optionally through incineration) in landﬁlls, while them. Accordingly, this fraction is open-loop recycled 58 kt (72.5%) is downcycled to low-value applica- to container glass, glass wool insulation or foam glass. tions. More speciﬁcally, the glass waste is used as ﬁller in recycled aggregates to produce concrete (e.g., for applications such as road constructions, foundations, pavements, etc.) (Debacker et al. 2021; DeBrincat and 123 E. Geboes et al. Fig. 4 Sankey Diagram of the post-consumer ﬂat glass ﬂow per origin, ownership, and application in Flanders, expressed in kilo- tonnes (reference year 2015). Results from and ﬁgure based on Debacker et al. (2021) Fig. 5 Picture taken by the author from a glass container on a typical Brussels demolition site Babic 2018; Dubois et al. 2013; Glass for Europe 2013; According to Debacker et al. (2021) and the inter- Hestin et al. 2016; Nodehi and Mohamad Taghvaee viewed deconstruction contractors, the advanced selec- 2022). The Sankey diagram in Fig. 4 illustrates the tive deconstruction method is typically used in large- post-consumer ﬂat glass ﬂow for Flanders per origin, scale renovation or demolition projects or sites that collection method, and application, based on Debacker include a large amount of ﬂat glass. Selective collec- et al. (2021). tion of glass is the result of advanced selective decon- struction methods. However, the interviewed recyclers mentioned that ﬂat glass is often mixed with other types Collection and applications According to Debacker of glass, like glass ceramics or glass wool insulation et al. (2021) and conﬁrmed by the interviewed decon- (Dubois et al. 2013). Furthermore, often other contami- struction contractors, the minimal selective deconstruc- nants, such as stones and metals, end up in the glass con- tion method is typically used for partial or complete tainer as well. Figure 5 shows a contaminated glass con- demolition of buildings in small-scale projects. This tainer at a typical Brussels site where the glass façade results in the non-selective collection of ﬂat glass. The of an ofﬁce building was demolished. This fraction is interviewed deconstruction contractors explained that typically open-loop recycled to produce i.a. container the ﬂat glass is crushed together with the mixed (stony) glass, glass wool insulation or foam glass (Debacker fraction during the minimal deconstruction method. et al. 2021). In some cases, fractions are so contami- This fraction is then sent to a recycling centre, where the nated (e.g., by the metal-containing spacer) that it ends most valuable materials (such as aluminium frames) are up in landﬁll (Ibid.). sorted out. However, the interviewed recyclers pointed out that it would be extremely costly to sort out the glass from the waste stream when it is crushed and mixed already. The contaminated batch is typically 4.2 Circular practices: sustainable waste management downcycled (Nodehi and Mohamad Taghvaee 2022; Rodriguez Vieitez et al., 2012). However, only moder- While some circular strategies are already part of the ate volumes of waste glass can be absorbed with down- business-as-usual (e.g., closed-loop recycling an open- cycling because the ﬂat glass waste acts as an impurity loop recycling), most of the (post-consumer) end-of- in the aggregates (Debacker et al. 2021; Heriyanto et al. life IGUs are still managed in an unsustainable way. 2018). These are thus low value, non-circular material Based on the interviews and literature study, this section streams and cannot be recycled again at their end-of- highlights the circular (niche) practices for end-of-life life. Accordingly, they are not considered circular or IGUs already present in Flanders and BCR. Further- sustainable processes (DeBrincat & Babic, 2018). more, additional circular practices are discussed which 123 Make or break the loop: a cross-practitioners review of glass Fig. 6 The four considered circular strategies (repair, reuse, repurpose, and recycle) with deﬁnitions adapted after Potting et al. (2017) and the corresponding actions following from the interviews with network actors are now absent in Flanders and BCR as well as the cir- cular practices that are already implemented in pioneer- ing projects outside Flanders. Figure 6 explains the four considered circular strategies—adapted to end-of-life IGUs after Potting et al. (2017)—and their actions—as discussed in the interviews with network actors. 4.2.1 Existing circular practices in Flanders and BCR Reuse of pre-consumer IGUs Besides the closed- loop and open-loop recycling practices of collected pre- consumer glass (cf. 3.1.1b), the reuse of pre-consumer ﬂat glass was pointed out as an alternative practice in Fig. 7 Environmental impact or beneﬁt per application—reuse, Flanders (Fig. 2). Practically, this implies the reappli- open-loop recycling, closed-loop recycling, low-value recycling, cation of brand-new IGUs that are discarded due to for landﬁll, and incinerator—of ﬂat glass waste (ine/tonne). Results instance surplus production or incorrect orders. from and ﬁgure based on (Debacker et al. 2021) The environmental impact or beneﬁt of the reuse strategy is mapped by Debacker et al. (2021) and is illustrated per application in euro per tonne in Fig. 7. After the MMG monetisation method (OVAM 2018), the outcomes clearly show the environmental beneﬁts of reuse compared to the environmental losses of down- was adapted during the design phase to the size of the cycling, landﬁll, or incineration. However, the reuse of reclaimed window (Opalis 2011). pre-consumer IGUs represents only one percent of the Furthermore, the feasibility to repurpose reclaimed total collected pre-consumer waste (cf. 3.1.1a). IGUs into outdoor purposes has been extensively stud- ied by Junger (2019). Junger focused on repurposing Repurpose of post-consumer IGUs One of the inter- the bronze-tinted glazing of the World Trade Centre viewed deconstruction contractors shared that they Towers in Brussels North Quarter into urban green- sometimes reclaim IGUs from a building’s façade to houses. Since the glazing of the 1970s does not corre- repurpose them into furniture, partitioning walls, doors, spond to current passive standards, an alternative use greenhouses, winter gardens or verandas. This inter- was sought in which the glazing could be still used to vention, however, can require space to store and reman- form a thermal barrier or buffer space between the out- ufacture the IGUs. An example from practice, found in side and the heated living space. Her research showed vulgarizing publications, is the construction of Number that repurpose in greenhouses is feasible in this case Nine Studios in Gentbrugge. In this project, a double- if a certain level of remanufacturing was performed glazed unit was found on-site and was repurposed as (Junger 2019). Yet this study remained theoretical and an indoor partitioning wall. The load-bearing structure was not executed in practice. 123 E. Geboes et al. Open-loop recycling of post-consumer IGUs Open- the need to seal the glass sheets in the post-war period, loop recycling (i.e., to glass wool insulation, con- however their use has remained marginal. tainer glass and foam glass) is already—but only A more recent example of such an alternative tech- marginally (27%)—present in the conventional prac- nique is the theoretical work of Mohamed (2020), tices (cf. 3.1.2b) (Fig. 4). During the interview, the called the Re-seal Window. The weakest part of the architect mentioned a large-scale project in which they IGU, the seal, is redesigned to increase the repairabil- had set the ambitions to closed-loop recycle the IGUs. ity of IGUs. In this design, the seal could be easily However, one of the interviewed manufacturers (also replaced every ten years so that the glass panes can involved in the project) explained that these IGUs could have a life span of more than 100 years. not be accepted for closed-loop recycling due to the Today, repairing IGUs remains a niche market and speciﬁc colour of the glazing. Since the production is often only explored for heritage or monumental process of container glass has less stringent quality- projects, such as the renovation of the Empire State requirements, the IGUs were instead open-loop recy- Building in New York and One Triton Square in Lon- cled to container glass. Practically, the IGUs were one don. These cases show that glazing can easily be by one removed from the building and collected in a reclaimed for repair purposes. As it is often claimed separate glass container, which was then brought to a about these cases, a local pop-up factory was set up to recycling centre. perform repairs of the damaged parts—the disassem- The advantage of open-loop recycling is that high bling of the unit to clean the glass panes, replace the concentrations of ﬂat glass waste can be recycled into seals and add new coatings, coated glass, or ﬁlms. After glass wool insulation and container glass, respectively the repairs, the glazing was re-installed in its original up to 90% and 60% of the raw materials (Dubois et al. façade (Jackson and Lanzarotto 2021; Koch 2013). 2013; Rodriguez Vieitez et al., 2012). This is partic- The repair strategy has many advantages as it pre- ularly interesting for lower quality cullet because less vents the replacement of glass units by interventions pure cullet is needed compared to the production of that extend their service life. Therefore, it allows sav- ﬂat glass (cf. 1.1). However, it is important to keep in ings in raw materials and energy (e.g., during produc- mind that glass wool insulation is an application which tion processes) and reduces waste generation. is currently not recyclable again (Debacker et al. 2021; Rodriguez Vieitez et al., 2012), while container glass, Reuse of post-consumer IGUs Although the reuse on the contrary, is fully recyclable. The European con- strategy for façade systems and components is very tainer glass recycling rates are the world’s highest, aver- well documented (Beurskens and Durmisevic 2017; aging 73% (Heriyanto et al. 2018). Gorgolewski 2008; Hartwell et al. 2021), the reuse of post-consumer IGUs is lacking in practice. The inter- 4.2.2 Missing circular practices in Flanders and BCR viewed deconstruction contractors mention that there is currently no market demand for reclaimed IGUs for Repair of post-consumer IGUs The repair of glaz- reuse. Souviron et al. (2019) point out: “reuse of win- ing was once common practice, but this changed since dows are more or less anecdotal, partly because the the breakthrough of the IGU in the 1970s. New failure technical obsolescence of the product recovered, but issues arose with the IGUs, such as condensation issues also because of damage caused by disassembly and and a lowered thermal performance. Souviron (2021) transportation.” explains “cleaning and repair are almost impossible due to the sealed assembly of the two panes, which prevents their separation and thus access to the interior cav- Closed-loop recycling of post-consumer IGUs ity. The replacement of units then becomes necessary, Despite the lower environmental beneﬁt of closed-loop being also favoured by government energy policies and recycling compared to other open-loop processes (see by the glass industry itself, as both promote the use of Fig. 7), two interviewed researchers and deconstruc- new and more efﬁcient products (for example, low- tion contractors advice to give priority to closed-loop emissivity glass, argon insulation, self-cleaning coat- recycling for two reasons. First, in the open-loop recy- ings, ultra-clear glass, etc.)”. In this work, Souviron cling processes the ﬂat glass downgrades irreversibly looks at several alternative techniques that circumvent to another product (cf. 1.1). Second, the percentage of 123 Make or break the loop: a cross-practitioners review of glass ﬂat glass cullet that is used as secondary raw mate- glass container for selective collection. Third, the logis- rial in the ﬂoat process—now reaching 30%—can be tical feasibility depends on the scale of the project. For increased if also post-consumer ﬂat glass waste would instance, in smaller projects, the quantities of ﬂat glass be accepted (DeBrincat and Babic 2018). However the collected are often not enough to ﬁll a full ﬂat glass demand of ﬂat glass manufacturers for high-quality ﬂat container (Debacker et al. 2021; Dubois et al. 2013). glass cullet, the supply seems not to be met. And last, interviews with one researcher and recycler A unique example however shows that closed-loop indicate that, in Flanders and BCR, the distance to the recycling of ﬂat glass is feasible. The Lloyd’s project stone processing plant is often shorter than that to a in London was the ﬁrst to input such an enormous glass processing plant, which makes it logistically and amount of post-consumer glass—approximately 123 ﬁnancially more interesting for demolishers to mix the tonnes—into the ﬂoat process (Bowers and King 2013). ﬂat glass waste with the stony fraction (Debacker et al. Bowers and King (2013) explain: “This represented 2021). This implies that a network with local collection a high degree of environmental responsibility, as dis- points for ﬂat glass is lacking in Flanders. carding such a quantity of glass would have been very wasteful.” 5.1.2 Opportunities The two mentioned case studies illustrate that logistical 5 Barriers and opportunities barriers can be countered in some cases, e.g., by cre- ating a pop-up factory to remanufacture and store the The above-discussed circular practices remain niches. reclaimed insulated glazing nearby the site (cf. 3.2.2a) (Jackson and Lazzarotto 2021). Sharing the knowledge In identifying the barriers and opportunities to scale of these case studies will highlight how they deal with up these practices, ﬁve central themes emerged from the cross-practitioners’ interviews and literature study: logistics and timing in their project. Often, for instance, space can be reserved on-site (in large-scale renovation organisation, (material-) technical aspects, ﬁnancial aspects, legislation, and mentality and knowledge. Fig- or (de)construction projects) or nearby the site (e.g., available public storage) with minimal effort. ures 8 and 9 map, respectively, the encountered barriers and opportunities that were mentioned during the inter- The interviewed ﬂat glass manufacturers, recyclers and collector mentioned how the foundation of Vlak- views per theme. glas Recycling Nederland in The Netherlands counter logistical barriers with a recycling fee for imported and 5.1 Organisation produced insulated glazing (Wittekoek 2020). The ini- tiative allows contractors to deposit ﬂat glass waste free 5.1.1 Barriers of charge at local collection points, therefore, making it easier for the contractor to choose advanced selective From the interviews and literature study, within the dis- collection. It was the collaboration of network actors persed supply chain of IGUs, there is only limited col- that led to a successful up-scaling of the logistical sys- laboration between the different network actors. How- tem for recycling ﬂat glass. The interviewed ﬂat glass ever, collaboration is key to valorise end-of-life IGUs. manufacturers explicitly indicated that they were open For instance, reclaim and reapplication of the materials for such collaboration and participation in a similar can only be achieved when the construction team and system. deconstruction team collaborate; matching the poten- Furthermore, the interviewed deconstruction con- tial reuse materials with the actual reclaimed materials tractors explained how they underwent a shift of their and searching for a sales market. initial role (from demolishing IGUs—initial role—to Furthermore, several issues arise concerning the col- reclaiming and reselling them—new role) to contribute lection and reclamation of IGUs. First, the interviewed to a circular economy. This allows the actors to act deconstruction contractors complain that often insufﬁ- within different stages of the life-cycle, e.g., product, cient time is planned to realize this. Second, the inter- construction and end-of-life phase of the IGU. For viewed architect claims that often there is a lack of stor- instance, by introducing take-back systems, a logis- age space to store the reclaimed IGUs or to place a ﬂat tical system that the interviewed manufacturers want 123 E. Geboes et al. Fig. 8 Overview of the barriers categorised per theme to experiment with further. In fact, to take back mate- connections was raised as a difﬁculty for valorisation rial for i.e., recycling, has many beneﬁts for the glass –disassembly is required for recycling and repair, and producer, like lower energy consumption and cost, and optionally reuse and repurpose. Besides, the disassem- savings in virgin materials (cf. 1.1). bly of an IGU is a dangerous task because of the mate- rial properties of glass; it is fragile and breaks easily. The limited technical service life of the IGU is men- tioned by the architect and contractors. The gradual 5.2 (Material-) technical aspects drop in thermal performance leads to questions about how the quality and performance of such a second- 5.2.1 Barriers hand product can be guaranteed. The quality needs to In the interviews with the recyclers and researchers, the complex disassembly due to the irreversibly glued 123 Make or break the loop: a cross-practitioners review of glass Fig. 9 Overview of the opportunities categorised per theme be reassessed, yet an approach to validate the perfor- State Building, Lloyd’s building, One Triton Square, mance of reclaimed IGUs is not yet developed among etc., illustrate that with tailor-made infrastructure, the network actors, nor in policy implemented. disassembly, remanufacturing, and re-assembly of end- of-life insulated glazing is technically feasible, despite the complex assembly. More research and experiments 5.2.2 Opportunities are needed into the remanufacturing possibilities of The technical end-of-life possibilities of IGUs are promising: once disassembled the glass panes are fully recyclable and can be re-assembled for reuse or repur- pose. Case studies like the renovation of the Empire 123 E. Geboes et al. end-of-life IGUs and the corresponding quality and per- so the selective collection or reclamation of ﬂat glass formance of the repaired, reused, or repurposed prod- waste, can be ﬁnancially beneﬁcial for projects con- uct. Moreover, redesigning the IGU’s irreversible con- taining large amounts of IGUs. To illustrate the feasi- nections (cf. 3.2.2a) would facilitate the disassembly bility to the industry, more project examples and initia- process signiﬁcantly. tives from the actors are needed in Flanders and BCR. The interviewed deconstruction contractors stated Charging a recycling fee, as successfully introduced in that the reclamation of IGUs from buildings is facili- The Netherlands (Wittekoek 2020), can make circular tated by window beads (present at most window frames, strategies ﬁnancially feasible on a large scale. such as PVC and metal window frames). This reversible connection allows fast demounting. 5.4 Legislation 5.4.1 Barriers 5.3 Financial aspects The interviewed researchers mention a lack of regula- 5.3.1 Barriers tions for advanced selective collection of glass and for the implementation of circular strategies. For instance, A major bottleneck that the interviewed network actors for Flemish and Brussels’ deconstruction contractors encounter today is the ﬁnancial feasibility of the circu- there is no legal incentive to selectively collect or lar strategies. The interviewed deconstruction contrac- reclaim IGUs, besides the technical prescriptions for tors mention that labour costs for the advanced selec- glass in recycled aggregates (PTV406) (COPRO vzw tive deconstruction method (e.g., reclamation, disas- 2020). In addition, the interviewed architect com- sembly, and other interventions), and logistic costs for plained about inﬂexible regulations for energy perfor- the selective collection (e.g., separate container, infras- mance in buildings that make the implementation of tructure, transport, and storage) are high in Flanders reused materials, such as reclaimed IGUs (with no qual- and BCR. Labour taxes are the highest in Belgium, the ity guarantee), almost impossible. tax wedge for the average single worker reaches up to 52.6% (OECD 2022). In addition, Debacker et al. 5.4.2 Opportunities (2021) explain that “the price difference between pri- mary and secondary raw materials remains too small In Flanders and BCR, a demolition inventory must be […] to stimulate (advanced) selective demolition and carried out if a building is demolished. The main task of separate collection.” this demolition inventory today is to identify hazardous If not done manual, to repair, reuse, repurpose waste materials so that they can be removed from other or recycle IGUs sometimes expensive techniques or building materials (Debacker et al. 2021). However, it infrastructure are needed (e.g., expensive tailor-made does not mention how non-hazardous waste materials machinery for disassembly, expensive sorting tech- should be collected or if it is obliged to collect a non- niques to sort out contaminants, etc.) An investment hazardous fraction separately. One of the interviewed that the interviewed recyclers and deconstruction con- deconstruction contractors and researchers suggested tractors are not willing to make because of the low that the demolition inventory could instead support the ﬁnancial value of ﬂat glass. A ﬁnancial incentive is implementation of circular strategies. For instance, to thus missing. identify the reuse potential and repair, repurpose, or recycling possibilities of end-of-life insulated glazing. 5.3.2 Opportunities The scale of a project can have a signiﬁcant inﬂuence 5.5 Mentality and knowledge on logistical costs. Debacker et al. (2021) explain for Flanders and BCR: “the proportion of transport costs 5.5.1 Barriers in relation to the total cost decreases by 19% for the advanced selective deconstruction of 23 houses instead According to the interviewed network actors, in gen- of one house.” Advanced selective deconstruction, and eral there is insufﬁcient knowledge and awareness 123 Make or break the loop: a cross-practitioners review of glass among network actors about the circular strategies and circular strategies are marginal in the Flemish and their implementation, especially concerning technical Brussels conventional construction practices. Yet, at a aspects. The traditional demolition approach—which small scale, the circular strategies repurpose and open- refers to the minimal selective collection method—and loop recycling of end-of-life IGUs are being success- more speciﬁcally the conservative attitude of most fully explored. In contrast to post-consumer IGUs, pre- demolition companies, is pointed out as a barrier by consumer ﬂat glass waste from IGUs is already com- the interviewed recyclers and manufacturers. pletely recycled or reused at high-value. Furthermore, including reclaimed IGUs for reuse in Second, repair, reuse and closed-loop recycling a design requires a totally different approach than the are circular strategies absent in Flemish and Brussels traditional design approach (Beurskens and Durmise- construction practices. However, pioneering projects vic 2017). “Reclaimed materials do not show up at the from other regions illustrate the viability of repair and right time, in the right amount or the right dimensions” closed-loop recycling of post-consumer IGUs. Reuse conﬁrms Gorgolewski (2008). remains unexplored. Third, the barriers and opportunities to the up- scaling of the circular strategies are identiﬁed per theme 5.5.2 Opportunities by interviewing 13 network actors and researchers. In general, the main organisational barriers are limited Some of the interviewed recyclers and all deconstruc- collaboration between actors (e.g., between construc- tion contractors requested speciﬁc training for labour- tion and deconstruction teams, and between recyclers ers and organisations. For instance, to educate them on and manufacturers), challenging logistics (e.g., lack of how to collect and reclaim IGUs properly and safely. storage space to store reclaimed or collected glass, and As sector federations, e.g., of the construction sector, lack of local collection points), and time and cost pres- glass sector, etc., already play a role in the conventional sure that hinder the disassembly of IGUs. However, practices to give advice and sometimes workshops to sharing knowledge from case studies can help facilitate network actors. This could be an opportunity to reach the implementation of circular strategies in construc- out to the network and share technical, logistical, and tion practices. Also, network actors are experimenting other knowledge to valorise end-of-life IGUs. with take back systems and role shifts to act within Mental and behavioural changes are needed among multiple life-cycle stages of the IGU. The material- the network actors to valorise end-of-life IGUs. technical constraints, speciﬁc to IGUs, are its com- For instance, pioneering projecs show innovative plex assembly and uncertain quality and performance design approaches for repurpose of reclaimed IGUs at the end-of-life. Redesigning the unit would facilitate (cf.3.2.1b). Additionally, interviews with the network this process, however, successful cases prove that these actors show that there is already some interest and technical challenges can be surmounted. At a systemic, demand to valorise end-of-life ﬂat glass. economic level, high labour, and logistic costs (e.g., Furthermore, Debacker et al. (2021) advise to disassembly is labour intensive, higher costs for stor- increase the research and knowledge on material age and transport of reclaimed or collected glass, etc.) streams on the part of government and policymakers, and expensive techniques or infrastructure to reclaim or so that material streams can be better controlled, and process glass contribute to the lack of ﬁnancial incen- strategic decisions can be substantiated. tives for network actors in Flanders and BCR. Large scale projects and legal ﬁnancial incentives can reduce 6 Conclusion these ﬁnancial challenges. In general, legislation for selective collection is missing and should be intro- With a speciﬁc focus on the end-of-life stage of IGUs, duced, for instance in an updated, obliged demolition this exploratory study gives, for the ﬁrst time, an inventory. Further, sharing knowledge and providing overview of Flemish and Brussels conventional and cir- training for labourers can change the conservative atti- cular construction practices with corresponding barri- tude of labourers and improve insufﬁcient knowledge ers and opportunities. and awareness of applying circular practices among First, following other studies, the priority must be network actors. set on how to valorise post-consumer IGUs, hence, 123 E. Geboes et al. Finally, the insights of this study—innovative niche and reversible buildings: conference proceedings. Sarajevo Green Design Foundation. https://greendesignconference. practices, barriers and opportunities for the network com/gdc2017/ (2017). Accessed 17 October 2022 actors, and cross-practitioner insights in ongoing prac- Bowers, M., King, P.: “Lloyd’s Cloudless”: reglazing Lloyd’s of tices—are the basis for further research in how to close London - a ﬁrst for recycling. Arup J. 84–89. https://www. the material loop for IGUs. For instance, which condi- arup.com/perspectives/publications/the-arup-journal/ section/the-arup-journal-2013-issue-2 (2013). Accessed 17 tions are required to upscale or replicate current local October 2022 niche practices; but also, how to bring other—currently Butler, J.H., Hooper, P.D.: Chapter 15 - Glass Waste. In: Letcher, absent—niche practices to the Flemish and Brussels T.M. and Vallero, D.A. (eds.) Waste (Second Edition). region. pp. 307–322. Academic Press (2019). https://doi.org/10. 1016/B978-0-12-815060-3.00015-3 COPRO vzw: PTV 406 (9.0) Prescriptions techniques pour Acknowledgements We would like to thank all the partici- granulats recyclés, COPRO. https://www.copro.eu/en/ pating interviewees for their valuable input and feedback. This document/ptv-406-90-prescriptions-techniques-pour- research was funded by Fonds Wetenschappelijk Onderzoek granulats-recycles (2020). Accessed 17 October 2022 (FWO), Grant Number 1S20722N Debacker, W., Vrijders, J., Voorter, J., Vergauwen, A., Bergmans, J., Stouthuysen, P.: Urban Mining van gebouwen. Naar het Author contribution The conceptualization, the outlining of the creëren van waarde via het sluiten van materiaalstromen. methodology, the original draft preparation and the making of the Circular Flanders. https://vlaanderen-circulair.be/nl/blog/ ﬁgures was performed by E.G; For writing—review and edit- detail-2/wat-als-we-opnieuw-bouwden-met-35-van-het- ing, E.G. and W.G. were involved. The study was supervised by afval-in-vlaanderen (2021). Accessed 17 October 2022. N.D.T. and W.G. All authors have read and agreed to the pub- DeBrincat, G., Babic, E.: Re-thinking the life-cycle of archi- lished version of the manuscript. On behalf of all authors, the tectural glass. ARUP. https://www.arup.com/perspectives/ corresponding author states that there is no conﬂict of interest. publications/research/section/re-thinking-the-life-cycle- of-architectural-glass (2018). Accessed 17 October 2022 Data availability The datasets generated during and/or anal- DeBrincat, G., Surgenor, A., Holcroft, C., Gill, P.: Build- ysed during the current study are not publicly available due to ing glass into the circular economy - how to guide. UK conﬁdentiality reasons but are available from the corresponding GBC. https://www.ukgbc.org/ukgbc-work/building-glass- author on reasonable request. into-a-circular-economy/ (2018). 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Glass Structures & Engineering – Springer Journals
Published: Nov 27, 2022
Keywords: Insulating glass unit; Circular economy; Waste management; Circular valorisation strategies; Closed material loops; Barriers; Opportunities
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