Circular economy for durable products and materials: the recycling of plastic building products in Germany—status quo, potentials and recommendations

In a first step, it was identified which individual construction products made of plastic are on the German market. To obtain an overview of the material-specific plastic diversity in buildings, the types and quantities of plastic used were identified for each product. This market analysis is the starting point for the further investigations.

The lists of harmonized specifications (hEN and EAD) derived from European Construction Products Regulation (EU) No. 305/2011, as well as the administrative regulation template for technical building regulations (especially parts B, C and D), initially served as the basis for the compilation of the comprehensive product list of plastic construction products used [9, 10] Those lists were reviewed with respect to construction products predominantly plastic- or bitumen-based. The relevant construction products were noted and included in the product list. To ensure the clarity of the compiled product list, the construction products being evaluated were classified into four levels (see chapter results and discussion). After identifying the various plastic construction products, an assessment of current market volumes (in terms of quantities produced and installed) was conducted. For the time being, data from the production statistics of the German Federal Statistical Office according to the list of goods (nine-digit data) were used as the basis for the production quantities [11]. However, a review and assessment quickly indicated that the data from the Federal Statistical Office alone is insufficient for clearly allocating the varying production volumes to the respective construction products researched. Through the use of the various association and industry statistics, along with data from specialist literature and the Federal Statistical Office, it was possible to make an initial determination of the quantities currently installed in German buildings. In interviews with industry experts, manufacturers and associations, the quantities determined in this manner could be confirmed or supplemented.

To determine the dynamics of the anthropogenic stock of building products made of plastics, the quantities determined above were offset against data on the growth of plastic processing in the construction sector. These data were drawn from a biennial survey of the plastics market. The development of the input into the anthropogenic stock could, therefore, be based on the specifically-determined amount consumed in 2017, and could be calculated retroactively back to 2003. Data from the waste statistics (Technical Series 19) of the Federal Statistical Office were used for the output-side analysis of the stock list [12]. The following waste types associated with construction and demolition waste were considered relevant: Plastics from construction and demolition waste (waste code: 170203), mixed construction and demolition waste (waste code: 170904), insulation materials (waste codes: 170603 and 170604), cable waste (waste code: 170411), and plastic waste (excluding packaging) from the gardening and landscaping sector (waste code: 020104). It can be assumed that the wastes listed under codes 170203 and 020104 are exclusively plastics. The corresponding proportion of plastics for the other waste types was estimated on the basis of different statements from experts and plausible assumptions.

An estimate of future developments was made for both the input- and output-side considerations to be able to draw conclusions regarding the future development of return flows from the stock list.

For more detailed information on the assumptions and calculations compare chapter 2.1.1–2.1.3 of the study, this report is based on [13].

In take-back systems, products are recovered following their use phase. Take-back schemes can take different organizational forms, such as deposit systems, loan models where products are rented out, or simple take-back. There are several take-back systems in the German construction sector. The goal of the analysis was to provide a comprehensive list of the individual systems and their characteristics. Furthermore, the basic conditions for functioning recovery systems should be identified to derive recommendations for their successful application and transfer on other products. Information was compiled from literature, expert interviews and data available online.

In Germany, mechanical recycling of plastic products is widespread. Since plastic building products are very diverse, the aim of reviewing the German recycling sector was to identify which processes are most suitable for construction products and to make recommendations for increasing recycling. This was done through research in specialist literature and expert interviews.

To outline the potential use of recyclates in plastic construction products, the general prerequisites for the use of recyclates in the manufacturing of building products were examined in detail. Due to their high relevance, pipes in particular but also cable ducts, are considered, with current standards and requirements for the use of recyclates being explained and the technical limits and further obstacles outlined. Based on this, an assessment was made of the potential use of recyclates in the four major application areas of pipes, profiles, insulation materials, and others.

In Germany, the total quantity of installed construction products made of plastic was 2.64 million t in 2017. The shares of the aggregated application areas are shown in Fig. 1.

In the pipes sub-segment, the data situation was mostly satisfactory. In addition to the data from the production statistics, the statistics of the Trade Association of the Plastic Pipe Industry were used as a supplement to determine current market volumes. A review and evaluation of the data indicated an annual production volume of around 1.03 million t of plastic piping, with pipes made of polyethylene and polyvinyl chloride accounting for the largest share in terms of overall mass. The installed mass was estimated to be around 0.81 million t per year (see Fig. 1) of which around 0.30 million t comprised PE, 0.19 million t PVC, 0.08 million t PP, 0.05 million t GFRP, and 0.19 million t of plastics that could not be precisely identified [11, 14, 15].

For the profiles sub-segment, the production in 2017 was around 0.91 million tons. Profiles are continuously extruded semi-finished products that are then used to manufacture final products such as the frames of windows or doors. The material most often used here was PVC. Due to a very high export surplus within this sub-segment, the mass was estimated to be around 0.57 million t (see Fig. 1) of which around 0.41 million t comprised PVC, 0.02 million t GRP, 0.11 million t PE, and 0.03 million t of plastics that could not be precisely defined [11, 14].

In the insulation sub-segment, data from technical literature and associations (e.g., from interviews with experts) were mostly used [16, 17]. It should be noted here that the obtained information mostly refers to the three insulation material types of expanded polystyrene (EPS), extruded polystyrene (XPS), and polyisocyanurate, respectively, polyurethane. No information was available on the market quantities of other insulation materials (e.g., those made of phenolic resin rigid or polyethylene foams), although it was confirmed during the expert interviews that these make up a negligible proportion in terms of the total quantity of insulation materials installed.

For the last sub-segment, others, the production mass of waterproofing materials, floor coverings, and cables are especially relevant. Due to their versatility and the large number of different products in the sub-segment, the availability of data on the current market quantities of the different construction products turned out to be highly heterogeneous. Therefore, to estimate the quantities of waterproofing membranes, floor coverings, and cables, data from the technical literature or corresponding association statistics was utilized. For data on other products belonging to the others sub-segment, production statistics were employed [11, 14]. The installed volume for the sub-segment others was estimated to be approximately 0.782 million t, of which bitumen-based roofing, plastic roofing and waterproofing membranes accounted for around 49% [18, 19]. The remaining production mass could mainly be attributed to floor coverings (around 23%) and cable materials (9%) [20].

After aggregation of the sub-segments of pipes, profiles, insulation, and others, the shares by plastic type corresponds to the installed volumes (2.64 million t) in 2017, as shown in Fig. 2. Around 30% of the installed volume could be attributed to PVC plastic, and around 16% to PE. Other plastics of particular relevance in terms of volume include EPS (8%), PIR/PUR (5%), PP (4%), and GFRP (3%).

Based on the methodology described above, the past and future development of the anthropogenic stockpile of building materials made of plastic have been estimated. The total waste volume for the period between 2005 and 2017 was around 7.94 million t (see Fig. 3). At 6.4 million t, the plastics contained in mixed construction and demolition waste (waste code: 170904) make the largest share of waste mass. Additionally, around 0.4 million t of plastic cable waste (waste code: 170411) and around 0.2 million t of insulation materials (waste codes: 170603 and 170604) accrued in that period of time. Both, plastic from cable waste and plastic from insulation materials were collected together with other cable and insulation material. Only 1.16 million t of plastics (14.6%) were collected separately (waste codes: 170203—plastic waste collected separately from construction and demolition waste and 020104—agriculture, horticulture, pondmanagement, forestry, hunting, and fishing).

The net input (input minus output) of the anthropogenic stockpile in the period between 2005 and 2017 can thus be estimated to have been roughly 22.4 million t. This corresponds to an average annual increase of 1.7 million t (see Fig. 4). The projection by 2030 indicates that the anthropogenic stock will roughly double by 2030 compared to 2005. The application of plastics in the construction sector definitely increases. These extrapolations are based on the available data and should be treated as a rough estimate. Nevertheless, the amount of plastics applied in the construction sector will definitely increase and thus the anthropogenic stockpile too.

The large difference between the volumes of plastics consumed and those generated as waste in the construction sector is primarily a function of the industry-specific service live times of the various product types and the increased use of the material in the construction sector in recent decades. Compared to plastic products from other sectors, such as packaging (typical service lives of a few days or weeks), plastic-based construction products are characterized by significantly longer service lives and, in some cases, remain in the building stock for several decades. A large part of the waste currently generated during dismantling was installed many decades ago. Plastic products currently being used will, in turn, not emerge in the waste stream for several decades. This state of affairs represents a major obstacle to holding manufacturers responsible under the ‘polluter pays’ principle, or implementing manufacturer-supported take-back and recycling systems for currently returning streams. The utility of the mechanical recycling of current and, from today’s point of view, partially contaminated post-consumer waste, must also be examined on a case-by-case basis and, depending on the ingredients that were initially used. On the other hand, longevity as such already offers ecological advantages over the use of plastics in products with short service lives.

Take back systems offer the following solutions to improve high-quality recycling:

On the other side, the implementation of take-back schemes has some challenges that need to be considered

The following criteria that recycling of plastic construction materials have to face in general apply to take-back schemes as well

Different take-back schemes have been analysed. Most of them are focused on the sectors of PVC, floor coverings and agricultural films, compare Table 2. For insulation materials, no larger scale take-back system exists. PVC-U take-back systems function well for window and door profiles. Here, considerable amounts are taken back and recycled in a controlled loop. For pipes, a suitable recycling process exists as well but here the difficulties of separation during dismantling together with long product life time result in lower relative amounts that are recycled. While PVC-U take-back systems are organized industry wide, take-back systems for textile floor coverings are implemented by just a few companies. Those carpets are reused or downcycled to carpet backings. Additionally, in particular agricultural films, are collected and partly recycled to films again in considerable amounts.

In general, it can be stated that the implementation of take-back systems is a good prerequisite for high-quality recycling and should be supported if the circumstances are suitable.

Literature research and expert interviews showed that the recycling of thermoplastic plastic building products typically proceeds as follows:

Besides mechanical recycling, other techniques of high-value recycling are solvent-based processes and chemical recycling. In general, mechanical recycling is the most sustainable method. Solvent-based processes can be a suitable solution in cases where recycling-incompatible substances, for example additives, need to be removed from the waste stream. An example for a solvent-based process is the creasolve process which was in pilot stage during the study but went bankrupt in march 2022. The process carried out consists of dissolution, cleaning, precipitation and extrusion. The solvent is purified by distillation and then regenerated and reused [23, 24]. The additives to be removed depend on the feedstock, for building products the flame retardant HBCD plays a major role. Chemical recycling is still in development but experts agree that it should only be used for waste streams that cannot be mechanically recycled and would otherwise be discarded as substitute fuel. It remains to be seen whether it can serve this purpose from a sustainability perspective.

The choice of recycling techniques depends strongly on several factors, the important ones being

In general, it can be stated that PVC-U, e. g. from windows and doors as well as most forms of pipes and agricultural films are recyclable by means of available recycling structures and techniques. Floor coverings have the potential to be recycled to high-quality products if they are designed for recycling, e. g. by a wear layer made of a single material. Recycling of PIR /PUR insulation products is challenging as well. Here the low mass of the product, the difficulties of separation during dismantling and the non-thermoplastic nature of the material are to be considered. Significant difficulties arise for GFRP since neither the fibers nor the resin are recyclable so far.

The recycling of plastic building products can only achieve its full potential when it is taken into account throughout the whole product life cycle and by all involved stakeholders. It includes, for example, using design-for-recycling principles during product design and using appropriate techniques in the building process which allow for disassembly and separation at the time of dismantling. Especially glued, or subterranean installed products are hard or impossible to recover in a financially viable manner.

The long product life time makes these considerations on one hand especially important, because products being used now will reach their end of life stage at a point of time where a circular economy is expected to be state of the art. On the other hand, long product lifetimes pose a significant challenge because regulations and recycling techniques might change considerably up until the time when the product enters the recycling phase.

In general, it can be stated that for many products the possibility of recycling exists but this goal must be pursued by all stakeholders of the value chain and will most likely result in significantly higher costs for these stakeholders.

For more detailed information on the process of obtaining the primary information by literature review an interviews, see chapter 4 of the study this report is based on [13].

The recyclability of plastics is influenced by different properties. As plastic waste, especially in the post-consumer sector, accumulates as a heterogeneous mixture and the different types of plastic are often very difficult to mix with one another, separation into individual plastic fractions (for example, by means of near-infrared spectroscopy) is usually a mandatory prerequisite for the production of a high-quality recyclate. The enormous variety of plastic types, blends, colorants, and additives used often make this step significantly more difficult. Prerequisites for the use of plastic recyclates are summarized in the following bullet points:

Based on our research, the following recommendations can serve to improve plastics recycling in the construction sector. An in depth discussion can be found in chapter 7 of the report this paper is based on [13].

A product’s recyclate content as well as its recyclability are valuable information and should be included in technical documentations and product labeling on a mandatory basis. This information can function as a valuable guide for informed user decisions. At the same time, the cost and effort for their declaration is minimal. Where possible, the information may be passed along with the product based on digital markings such as a QR code or a watermark.

If, for reasons of low quantity availability, waste from the construction sector cannot be reused for the manufacturing of the same product (e.g. pipe-to-pipe), efforts should be made to utilize these materials for other construction products. Especially in the case of products that do not require proof of usability in accordance with Part D of the Model Administrative Rules on Technical Building Regulations [9] and for which there are no recognized rules of technology, there is still great potential for increasing the use of recycled materials.

High recyclate contents in packaging for building products should be promoted. The feasibility has been demonstrated in various products such as stretch and shrink film, big bags, pallets, canisters bottles and others [37‐40]. One way of promoting recyclate use could be a mandatory recyclate quota for films as proposed by various stakeholders. Another approach would be to strictly enforce existing regulations for separation of plastic waste at the building sites to cycle the packaging materials.

As stated before, high-quality recycling does not start at the waste stage of a product but needs to be considered in the production process as well. This means applying design-for-recycling principles and thus avoiding materials, material combinations and additives not suited for recycling. In the case of toxicologically critical additives this implies a conservative, anticipatory approach that takes into account the long product life times and changes of regulation in that time. Product design needs to consider dismantling and separation from the waste stream and to minimize packaging.

While regulatory approaches to enforce design-of-recycling are difficult to implement, all measures promoting or enforcing recyclate use will promote design-for-recycling principles in the long run as a trickle down effect.

Take-back schemes have been shown to provide very good opportunities for high-value recycling when they create well-defined closed loops. The establishment of take-back schemes should thus receive more scrutiny from the industry side. Research can here elucidate further suitable material streams and organizational parameters that can help to amplify the number of take-back schemes and to make them more efficient and profitable.

Even an efficient recycling process has a considerable ecological footprint. For products whose lifetime is governed by their durability, measures like extending product lifespan or improving repairability is therefore preferred to recycling from a sustainability point of view. In general, the use of plastic for building products is ecologically preferable compared to single use or short live plastic products. Nevertheless, especially against the background of the long lifetimes of building products, the long-term goals of the circular economy and also CO₂ neutrality in the middle of the century must definitely be kept in mind in the further development of building products made of plastic.