Introduction

The EU Horizon 2020 funded CityLoops project focuses on closing the material loops of two central sectors of any city in terms of material flows, societal needs and employment, namely the construction and biomass sectors. Due to their sizes, they represent a considerable opportunity for cities to transform their metabolism and economy towards a more circular state.

Within this project, seven European cities, amongst those also the City of Roskilde are planning to implement demonstration actions to kickstart their circularity journey. To better understand what the current circularity status quo is, as well as the impact of these actions, and the efforts needed to transform their sector, a Sector-Wide Circularity Assessment method was developed. This method combines a circular city and circular sector definition, a material flow and stock accounting method, as well as circularity indicators. The sector itself was defined in terms of a number of representative materials that make up a large share of the sector and associated economic activities. The construction sector is made up of 11 materials, depicted as icons here, which were studied along the entirety of their supply chains. Altogether, these elements help to set a solid knowledge and analytical foundation to develop future circularity roadmaps and action plans.

The assessment was carried out by the cities themselves after receiving extensive training in the form of courses on data collection (construction and biomass) and data processing. Numerous additional insights can be found in the individual Data Hubs of each city.

This current Sector-Wide Circularity Assessment report provides contextual information on the city and the economic sector under study. It then illustrates how circular these sectors are through circularity indicators and a Sankey diagram. Finally, it analyses and interprets the results, presents the limitations from the data used and offers recommendations about how to make this sector more circular.

(* The italic texts in this report were written by Metabolism of Cities' Aristide Athanassiadis and Carolin Bellstedt. They provide relevant general information and serve as connecting elements of the single report parts.)

Urban context

To contextualise the results of the sector-wide circularity assessment, this section provides population and land use information data of the city. In addition, population and area of the city under study, as well as its corresponding NUTS3, NUTS2 and country were included. Data for these scales were added to better understand how relevant and important the approximations are when downscaling data from these scales to a city level.

Population of Roskilde

Roskilde municipality is characterised by a steady increase in population, namely by 2.67% from 86,689 inhabitants in 2017 to 89,001 in 2021. Roskilde is a popular settlement municipality and the city's relocation rate has been continuously increasing, for example by 1,200 people from 2019 to 2020. Expressed in households, there were a total of 40,102 in 2020. Roskilde municipality is characterised by a population that is largely represented by the fact that there are more than twice as many with a long higher education as in the rest of the Region Zealand. Also measured in short and medium-term higher education, Roskilde Municipality is above Region Zealand. Roskilde University attracts a number of new citizens every year and a portion of those stay in the municipality when they start working. This is balanced by a growing portion of elders in the population, since the number of deaths are increasing.

As can be seen in the graphic below, the population is comparatively young with about 40.6% (2021) of them being 34 years and younger, while the largest number of people are in the 50-64 year olds age group.

Data source

Land use

Data source

The municipality is characterised by a mixed land use. Agriculture and nature fills up a significant part of the landscape. Low rise dwelling areas also dominate the land use. In 2021, there will be a special focus on changed land use, nature conservation and increased biodiversity on municipal land, cooperation on afforestation, further development of the nature areas close to the city, and improved access to nature.

Economic context of construction sector

This section puts into perspective the economic context of the sector under study. It describes how many people are employed in this sector, as well as who the main actors involved (from all lifecycle stages for the sector’s materials) are.

The construction sector in Roskilde

The construction industry plays a key role as the second largest industry in the municipality and contributes to the economic activity overall. The construction industry accounts for 13% of the total industry. The construction sector of Roskilde is characterised by many small to medium sized companies in the construction sector. Most are associated with rawmaterial production and typical craftmen.

The actors of the construction sector

The primary actors associated with material flows in the construction sector are: Nymølle, Roskilde Sten & Grus ApS, Munck Asfalt, Betonelement, DK Beton, and ARGO.

Extraction

A number of actors that deal with extraction of raw construction materials can be found in Roskilde. As seen on the map, there are a total of six companies present, most of which are gravel pit operation sites. Nymølle Stenindustrier A/S and Roskilde Sten & Grus ApS are the largest companies by employees with around 70 and 45 people respectively in 2019, whereas the other four companies have less than five employees. The so-called “Hedehusene” gravel pit (see image), though in the municipal boundaries of Roskilde and operated by Nymølle, is the largest gravel pit of Denmark. In 2020, about 2 million tonnes of gravel were excavated from that site. For over 100 years, gravel has been sourced from this area with different levels of quality that the Danish construction and infrastructure industry are dependent on. These gravel deposits have been deposited by huge meltwater rivers during the last ice age and cover a vast area from Roskilde west and all the way to Hedehusene in the east, containing an unusually high content of stones. Therefore, the municipality is well suited to produce a wide range of high quality sand, gravel and stone products to fit many different purposes, e.g. foundation, road construction, construction projects, as well as a contract for asphalt and concrete production​​ (Nymølle Stenindustrier A/S 2019).

Data source

Compared to Nymølle, Roskilde Sten & Grus ApS has not been in operation for so long, but also already for three generations. What began with the discovery of sand in their agricultural field in the 1970s and the initial operation of a gravel pit in Himmelev is nowadays a family-owned company that has excavated several areas in the vicinity of Roskilde. Since 1999, the primary excavation work has been at Øde Hastrup Vej (Roskilde). The area has since grown and the third generation, Anders Jensen, has taken over the day-to-day operations. The gravel pit delivers both for the very large construction and building projects, for the small craftsman, gardener, mason and contractor as well as for the private homeowner who has the opportunity to bring their own trailer and pick up materials (Roskilde Sten & Grus ApS 2021).

Manufacturing

The construction material related manufacturing industry in Roskilde is limited to two materials: bitumen/asphalt and concrete. For all other materials (aluminum, bricks, glass, gypsum, insulation, iron (steel), timber), there are no companies registered to be dealing with those in the municipality.

Asphalt

The main bitumen/asphalt company in terms of employees is Munck Asfalt with 27 people (2019). Founded in 1995, their business revolves around the manufacture of asphalt and the construction of roads and motorways. At the “Sjælland - Asfaltfabrik Svogerslev”, the asphalt plant which is located between Svogerslev and Lejre, approx. 8 km west of Roskilde, new asphalt is mixed in a batch operation with a 4 tonne mixer and a capacity of approx. 240 tonnes per hour. The site also has a crushing plant that receives old, broken asphalt and electric slag for crushing.

Next to Munck Asfalt, there is also the Dansk Støbeasfalt, with officially 9 employees, which has existed under this name since 1986 and was owned and operated by Vagn Rask for 25 years. Since then, Dansk Støbeasfalt has had an administration and factory in Roskilde. Since the end of 2011, the company has been owned by and operated as a subsidiary of the DAB Group AB, which handles membranes, sealing layers, cast asphalt and concrete renovation. The local subsidiary itself focuses on casting asphalt and moisture insulation (Dansk Støbeasfalt 2021).

The third company registered in Roskilde municipality to handle asphalt is Sjællands Emulsionsfabrik I/S (SE). SE is a production company that produces various bitumen based products. Typically, the products are used in the production and laying of asphalt. Other areas of application for SE products are, for example, gluing, grouting, moisture protection, impregnation and sealing. (SE 2021).

Concrete

As for concrete, there are two actors, namely Betonelement and DK Beton.

Betonelement is a subsidiary of CRH Concrete A/S, which manages several brands and employs approximately 1,300 employees in 11 factories throughout Denmark. CRH Concrete A/S is part of the international group CRH plc (approx. 80,000 employees in 30 countries). The Betonelement company is located in the south of Roskilde municipality, in Viby Sjælland, where it has the production site, as well as the headquarters of Betonelement and CRH Concrete A/S. There, it produces concrete and lightweight concrete with a special focus on concrete building elements that it also designs and installs as a service. Betonelement supplies all types of elements, from prestressed structures, over facades, walls, columns and beams, to complete solutions in both industrial, domicile and residential construction. Since recently, they can also deliver filigree decks, double walls, tunnel elements and prestressed bridges (Betonelement 2021).

DK Beton is the other company manufacturing concrete in Roskilde. While a national supplier with 17 locations that supply ready mix concrete, two of those sites are in the municipality, namely in Roskilde and Gadstrup. The company delivers both traditional concrete, floating / vibratory and set concrete in all strengths. Floor concrete, curb concrete, joint concrete and gravel concrete are also part of their supply. daily concrete delivery. Their customers range from private individuals to large contractors.

Retail and wholesale

There was no information provided on the companies registered in Roskilde that are operating in the retail or wholesale related to the construction sector. Oftentimes, the manufacturing companies are engaged in direct sales to other companies or contractors, thus skipping the step of a retail middle person. Moreover, even if the company names are known, it is generally very difficult to obtain data on sales volumes of materials. Therefore, the actors of this supply chain stage are disregarded.

Use

As for the actors in the use stage, the share of companies or private persons employing construction materials for construction or renovation work is unknown. Although there are permits for such work, it is not stated who carries it out, no less which materials and quantities for it are employed. In all likelihood the number of actors, especially in the form of small companies, is quite large. However, there is no overview of those. Even if there was, the local contractors’ shares of doing work within the boundaries of the municipalities vs. outside of it and those who aren’t registered in the municipality, but still conducting work in it are unknown.

Waste collection and treatment

The four main actors dealing with waste collection and treatment in Roskilde are all concentrated to the east of the center of the municipality, in industrial areas, close to highway 21. ARGO, an I/S waste company that treats waste for citizens and companies in nine Zealand municipalities, dominates waste processing in Roskilde. The company's primary task is to ensure that waste is converted into resources. The prioritisation is as follows: reuse before recycling before energy utilisation before landfill. As much waste as possible must be reused and recycled, and energy utilisation must take place in an environmentally sound manner and with the greatest possible benefit in the form of electricity and district heating. In Roskilde, ARGO operates two sites: a recycling center and a combined heat and power plant (CHP) called Energitårnet (energy tower), whose construction was finished in the end of 2013. The energy tower rises as a landmark for Roskilde and is surpassed only by the monumental cathedral. The CHP, which cost 1.293 billion kroner (166.6 mio. Euro), uses the waste that cannot be reused or recycled and with a utilisation rate of close to 100 percent, generates heat for the production of electricity and district heating. The district heating is sold to the transmission company VEKS, whose transmission network extends from Roskilde to Copenhagen and along Køge Bay to Køge.

Data source

Aside from ARGO, there are three other actors: Solum Roskilde A/S, Hedehusene Product Handel A/S, and Stena Recycling. These primarily deal with waste collection, the two latter ones especially with iron and metals, which they also trade.

Indicators

To monitor the progress of this economic sector towards circularity, a number of indicators were proposed and measured. Altogether, these indicators depict several facets of circularity of the sector. As such, they need to be considered in combination rather than in isolation when assessing circularity. In addition, these indicators can be compared to other cities or spatial scales (such as the country level). However, this has to be done with great care and use of the contextual elements in the previous sections of the report. Finally, the value measured from these indicators can be traced over time to track the sector’s progress towards circularity.

The domestic material consumption (DMC) is calculated by adding “Domestic extraction used” to “Imports” and subtracting “Exports”. For Roskilde, it amounts to 3,160,939 tonnes and 35.52 tonnes per capita. This value is quite high compared to the total DMC of ​​13.4 tonnes per capita for EU-28 in 2019 and still higher relative to the 24.98 tonnes per capita, in all of Denmark. However, those latter two also do take into account the total DMC and not just the materials used in the construction sector. Since it goes beyond the scope of this work to determine the share of construction materials in the total economy, it will not be further assessed. There are two main aspects that influence the DMC: (1) Probably the exported amount of extraction is under accounted for, meaning that not all that is extracted locally is also used locally, but likely transported to and used in other regions and (2) the “use”, which was indirectly determined through this high extraction value becomes very high in return, especially since the exports are not that high. These uncertainties are definitely a shortcoming.

The CMU value of indicator 39 stands at 9% and compared to the 12.4% for EU-28 in 2019 and 7.6% for Denmark, seems to be in line. However, since this indicator also includes the DMC, it must be assumed that the value is negatively affected as well. Another difficulty that is added to this indicator is that it was originally designed for metals. Since now materials from different categories are bundled up, it skews the image of the circularity of materials.

The EU self-sufficiency for raw materials indicator is very low with 1.01%. Unfortunately, there is no national value to compare it to. And since the data completeness was lacking in terms of differentiation of the single materials, this indicator couldn’t be calculated for them individually to determine the various self-sufficiency levels.

The EOL recycling and processing rates are still considerably low with about 14% and 30%, respectively. While 27% of materials are still subjected to disposal and 73% to recovery, the efficiency of recovery could still be improved. There is however uncertainty in those values, as the amounts derived from recycling had to be estimated.

The incineration rate is very low with only 1.75%. This is somehow surprising, as there is an incineration plant close by in Høje-Taastrup. On the other hand, construction waste materials are usually not subjected to a large extent to those facilities.

Finally, the landfilling rate is still quite high at 25%. The numbers came from the waste statistics and can be considered reliable, thus there is no uncertainty there. Either the municipality really still landfills quite a lot of waste, or the values are influenced by a lack of classification or differentiation of waste use on landfills as “alternative daily cover”.

Visualisations

Measuring circularity is a data heavy exercise. Numerous datasets were collected and visualised throughout the sector-wide circularity assessment process. To synthesise these findings, a Sankey diagram illustrates how material flows from the studied economic sector are circulating from one lifecycle stage to another. The height of each line is proportional to the weight of the flow. This diagram therefore helps to quickly have an overview of all the materials flows that compose the sector and their respective shares. The flows that are coloured in light blue in the Sankey diagram, are return flows. This means that they flow in the opposite direction of the lifecycle stages and are subjected to reuse, redistribution, or remanufacturing. Their size relative to the others is a good indication for the materials' circularity.

The Sankey diagram builds of course on the collected data that also the indicators have been derived from. Therefore, it needs to be taken into account that the previously discussed data quality influences also the quality and informative value of the Sankey diagram. In addition to the data quality, so-called allocation values also have an impact on the data behind the visualisation. These allocation values were employed to estimate the amounts of materials that “flow” between the single lifecycle stages, since these relationships and quantities were in most cases unknown, except for waste collection going to waste treatment.

Overall, the Sankey diagram for Roskilde shows that quite a lot of materials are moving around in the construction sector system. The share of materials for and from extraction really dominate the graph. About 30% of the materials (2 million tonnes) are extracted in the form of sand and gravel by one company, Nymølle Stenindustrier A/S, alone. The main share of it is subjected to export for retail outside of the municipality, while the other shares go to manufacturing, retail and direct use.

Compared to export, import plays a significantly smaller role. (It should be noted that the data quality and estimations of imports do have an impact on the image here, see the data quality section above.)

Manufacturing sees an inflow of materials from recycling and retail is fed with new materials from extraction, import and manufacturing, as well as secondary materials from incineration and use. This latter return flow from use back to retail could be surplus materials from construction sites that are labelled for reuse.

Going forward in the diagram from left to right, it can be seen that there is a data gap from the outgoing materials from retail to all other lifecycle stages. This reflects on the gap in the data availability described above.

Use is being fed by imported and extracted materials, although the majority would likely origin from retail, which can only be assumed due to the data gap. Most of the materials from use end up in stock, as constructed materials. While it may seem that quite a significant amount (677 kt) of the stock goes to waste collection and a little bit gets reused, this is only true in terms of the data of flows. It might seem that a lot of buildings and infrastructure get demolished again, but this of course isn’t the case. It is just that the Sankey diagram does not depict the stocks, the materials that stay in a system for over a year, but only the flows from the single stages.

While the waste collection node does receive most materials from the stock, it also gets inflows from imports and use. The diagram shows that the main share of materials leaves to recycling, which is also fed by imports and which has a comparatively large outflow as return flow to manufacturing. As for the other waste treatment options, landfill is quite high and very similar in size to storage of materials for recycling. Finally, a significant stream is from export to retail abroad.

Data quality assessment

Numerous datasets were collected and considered in the sector-wide circularity assessment. In some cases, datasets were not available for some materials or for some lifecycle stages for the studied sector. Therefore, estimations need to be done by looking at data at higher spatial scales (region or country). This section qualitatively assesses how reliable the data used is.

Data quality

Before describing data gaps and assumptions, the overall data quality is considered. It is expressed through four data quality dimensions that are depicted in the data quality matrix: reliability, completeness, temporal correlation, and spatial correlation. Each dimension has its own criteria for the ranking of high (green), medium (yellow) and low (red), which is based on this Pedigree report and shown in the table below. There can be additional explanations in some cells, as supporting information.

Data analysis

This section analyses the Sankey diagram developed in the previous section. It discusses and interprets the results for the sector-wide circularity assessment. It also reflects on how the current demonstration actions fit within the bigger picture of the sector, as well as how they could be upscaled to accelerate the transition towards a more circular sector.

References

• Denmark
• Sjælland
• Østsjælland
• Population of Roskilde, 2017-2021 line graph
• Static land use map of Roskilde
• Geo localisation of extraction companies in Roskilde
• Header image: Mariusz Paździora, CC BY-SA 3.0, via Wikimedia Commons