# Char from Pyrolysis of Waste Tires to Increase Bitumen Performances
## 4 Conclusions  
In this study, chars derived from the pyrolysis of waste tires were tested as green additives to improve bitumens' characteristics. This study explores the effect of pyrolysis flowing gases on the char characteristics and on the final bitumen performances. The motivation lies in the consideration that the type of the flowing gas can affect the chemical reactions taking place in the material under pyrolysis, especially at the surface, affecting the final char characteristics, and consequently the performances of the bitumen modified with it.  
Char addition brought about a significant increase in the rigidity under working conditions (i.e., \(G^{\prime}\) at 50 \({}^{\circ}\)C), especially at the char amount of 3 wt%, whereas the effect on the gel-to-sol transition temperature was found to be practically equivalent to that of a standard inert filler (CaCO\({}_{3}\)). In particular, the char derived from pyrolysis under CO\({}_{2}\), which was found to possess a greater surface and be constituted by smaller particles than that produced under N\({}_{2}\), showed a higher effect. The observed differences are attributed to the oxidizing environment (CO\({}_{2}\)) that is more aggressive and reactive in the synthesis phase compared to an inert environment (N\({}_{2}\)). This means that the modified bitumen has a stronger resistance against temperature, which may be advantageous for uses in certain (hot) conditions.  
Char also showed an anti-aging effect due to its high carbon content, which brings about greater compatibility of char with the organic nature of bitumen, and presumably its more effective hosting within the bituminous matrix. Self-consistently, the anti-aging effect was seen especially in the slowing down of the increase in rigidity upon aging, rather than in changes of transition temperatures. The anti-aging effect of the char is important because it prolongs the life-time of a bitumen and reduces maintenance costs.  
The work fills a void of knowledge related to the rationalization of the type of gas used during the process. Apart from the comparison of all the data, which will give important information for future char production and its application [15], the environmental benefit of this work needs to be emphasized, by considering that (i) pyrolysis can reduce the amount of urban waste and that (ii) longer-lasting road pavements reduce maintenance costs, and waste production, whereas improved bitumen can clearly bring about higher performing asphalt, which will be durable and conducive for road users.  
The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app14010030/s1](https://www.mdpi.com/article/10.3390/app14010030/s1)]([https://www.mdpi.com/article/10.3390/app14010030/s1](https://www.mdpi.com/article/10.3390/app14010030/s1)).  
Methodology, P.C. ([PERSON]) and C.O.R.; Software, M.P.; Formal analysis, G.C.; Investigation, P.C. ([PERSON]), A.P. and A.A.; Data curation, R.G.A.; Writing--original draft, P.C. ([PERSON]); Writing--review & editing, P.C. ([PERSON]); Supervision, C.O.R.; Project administration, P.C. ([PERSON]). All authors have read and agreed to the published version of the manuscript.  
Funding from @CNR Project ReScA \"Recupero degli scarti da pirolisi di rifiuti urbani per potenziare e ripristinare asfali\", decision of National Research Council of Italy, Administration Council, dated 21 December 2021.  
Informed Consent Statement: Not applicable.  
Data Availability Statement: Data is contained within the article.  
The authors declare no conflict of interest.