## 4 Conclusions  
The continuous growth of the world population is the main cause of generating a large volume of waste from industrial processes. Among these, cork waste from the manufacturing of bottle caps has not found any valorization application and is currently delivered to waste-to-energy plants. In order to face this problem, this work proposes its valorization as filler within lime-based mortars and polyurethanes, with the double objective of valorizing the waste and providing sustainability to traditional building materials. The cork waste under investigation was characterized through FTIR and STA and resulted in a mixed composition of cork (about 76%), paraffin and polyurethane glue (about 24%). The cork displayed a particle size distribution of 0.063 mm \(<\) d \(<\) 1 mm and a low apparent density of 340 kg/m\({}^{3}\). High water absorption (about 180%) was observed and considered for cork application within mortar. The addition of increasing contents of cork in mortars, i.e., from 1 wt% to 4 wt% (16 vol% to 65 vol%), gradually decreased the three-point bending and compressive strength of the reference mortar (0 wt%). However, the decrease in mechanical performance was less than expected, thanks to a continuous hydration promotion. In fact, the water absorbed by the cork during the mixing phase was later released over time and promoted better hydration of the binder. Therefore, better mechanical properties and less porosity of the final product were observed than expected. The apparent density of mortar mainly decreased with higher cork content, i.e., from 1820 kg/m\({}^{3}\) (0 wt%) to 1560 kg/m\({}^{3}\) (4 wt%). In conclusion, green mortars possibly suitable for the masonry restoration were obtained, with a reduced density by 15%. Lightness is a major property of restoration materials because it allows reduced loads applied to the pre-existing structure. The peculiar hygroscopic property of cork could be exploited for applications in dry environments, where too fast water evaporation, which could lead to the creation of cracks and early degradation, could be avoided by the release of water over time by cork. Cork contents up to 15 wt% (62 vol%) were considered within polyurethanes. Apparent density and thermal conductivity of polyurethanes containing cork slightly increased by 6 kg/m\({}^{3}\) and 0.01 W/mK, respectively. This is due to the fact that the cork fills the porosities that are usually filled with air and make polyurethane a highly lightweight thermal insulator. However, the thermal conductivity of these samples (0.03-0.04 W/mK) satisfied the requirements for the definition of thermally insulating material and standard insulating polyurethane (\(<\)0.06 W/mK). For both mortar and polyurethane, the addition of the cork waste also caused a color shift toward red-yellow color, which could be regarded as a positive aesthetic factor. In conclusion, this preliminary investigation allowed to identify possible alternative solutions to waste-to-energy of cork waste, thus making a so-far-linear economy circular and moving towards a more sustainable industry. The encouraging results displayed that it is feasible to valorize manufacturing cork waste as secondary raw material for construction materials and involve desired properties such as sustainability, lightness, coloring, etc., without affecting mechanical and thermal insulating performances. The companies involved in cork waste management issue can take advantage of these sustainable practices and valorize their manufacturing waste from an economic and sustainability point of view. Even though policies generally do not encourage the effective use of secondary raw materials in construction materials by strongly limiting their content or application use, this work points out positive performance that could be considered for real applications. Moreover, this study displays for the first time the properties of cork waste from the manufacturing of cork bottle caps and the influence of cork waste use in traditional construction materials.