# On the Road to Circular Public Procurement: Case, Variations, and Potential Actions in Germany
## 1 Introduction  
### Sustainable Development, Public Procurement, and Specific Product Considerations  
The development of global resource consumption and annual waste generation is expected to increase drastically over the next 30 to 40 years (see [1, 2]). Therefore, a change from the prevailing linear economy to a more resource-efficient way of adding value is one of the goals for which the model of the circular economy (CE) provides the framework [3, 4]. The CE model is based on the three dimensions of sustainability: environmental quality, economic prosperity, and social equity [3]. With regard to the goal of saving resources across material and product lifecycles and the associated benefits for the environment, society, and economy, the so-called R framework or R hierarchy is considered a key strategy. The 4R concept comprises reduction, reuse, recycling, and, finally, recovery. The concept can be refined by adding refuse, remanufacture, and repurpose activities into the structural concept [3]. In order to evaluate the most effective procedures for a specific case, sustainability assessments can be conducted. The implementation of a CE will cause fundamental transformations in many interconnected areas of our economy and society [4]. While various CE aspects of cars are analysed already--see, e.g., [5] for an overview--the implementation of a fully circular value chain is tricky in the case of tyres, not considering the area of public procurement. CE-related tyre treatment options were identified by [6]. The options are based on the extended R-framework. According to the principles of the CE, the implementation of theCE concept into the tyre value chain addresses all lifecycle stages from design to end of life, and requires the involvement of all relevant stakeholders. Valuable resources are needed for the manufacturing of tyres. The main compounds for the rubber are synthetic rubber, natural rubber, carbon black, silica-based compounds, and additives. During vulcanisation, these compounds are irreversibly crosslinked to a three-dimensional network and the rubber is converted into an elastomer [7]. Fabrics and steel wire are embedded for structure and strength. Natural rubber has been added to the EU's list of critical raw materials [8]. Therefore, research to on how to make tyre value chain more sustainable and circular is ongoing. Industry initiatives and research examine, for instance, alternative sources for natural rubber [9; 10] and carbon black [11; 12]. Other research topics regarding the sustainability of the tyre value chain include the recovery of carbon black or synthetic fabrics [13; 14]; the extension of the service life of tyres by tyre maintenance and usage behaviour (e.g., pressure control, driving behaviour) [15; 16], the improvement of retreading options [17]; the reduction of fuel consumption by introducing novel tire designs (e.g., EU tyre label); and finally, the preservation of materials in the material cycle through the recycling of EOL-tyres into secondary raw materials for various applications [5; 18; 19]. Despite these efforts, the potential for intensifying the tyre CE has not yet been exhausted, as many approaches still need to be transferred into practice or could be taken up more widely [4; 17]. At the same time, the acceptance of the use of new sustainable tyre variants (see, e.g., [20] regarding traditional acceptance problems of retreaded tyres) should be enhanced. In Germany, e.g., around 46 million used passenger car tyres are collected each year [13]. In line with [21], this article regards tyres that comply with one or more of these options and meet at least international working standards as'sustainable CE tyres'. In this context, specific attention is given to the treatment options remanufacturing via retreading and/or recycling. This article focuses on the potential of policy instruments and strategies for public procurement to promote a sustainable CE for tyres.