# Char from Pyrolysis of Waste Tires to Increase Bitumen Performances
## 3 Results and Discussion
### Bitumen Characterization
Looking at the data, the effect is at a maximum for char from CO\({}_{2}\) at 3% wt/wt, where the gel-to-sol transition temperature is increased by about 4.5 \({}^{\circ}\)C in the presence of CO\({}_{2}\)-char. For char from N\({}_{2}\), a slightly lesser effect is seen with a more uniform (flat) effect as a function of char% and with an increase in the gel-to-sol transition temperature of about 3 \({}^{\circ}\)C. It is seen that char from CO\({}_{2}\) gives an effect that is overall more dependent on the char%. Coherently, the penetration  
Figure 4: (**A**) Plot of G\({}^{\prime}\) and G\({}^{\prime\prime}\) as a function of temperature for a pristine bitumen (sample chosen as representative). The graphical derivation of G\({}^{\prime}\)@50 \({}^{\circ}\)C and T\({}^{\bullet}\) is shown by the pointing arrows. (**B**) G\({}^{\prime}\)@50 \({}^{\circ}\)C and T\({}^{\bullet}\) values as a function of composition. (**C**) Correlation between G\({}^{\prime}\)@50 \({}^{\circ}\)C and T\({}^{\bullet}\) for the bituminous samples discussed in the present paper (circles), and comparison with data from the literature (vertical bars, horizontal bars and crosses; see text for details). index, expressed in tenths of a millimeter, changes from 66 of the virgin bitumen (rif) to the following values for modified bitumen (3% wt/wt):  
* 58 for bitumen modified with N\({}_{2}\)-char;
* 57 for bitumen modified with CO\({}_{2}\)-char;
* 58 for bitumen modified with N\({}_{2}\)+CO\({}_{2}\)-char. This effect can be due to the fact that CO\({}_{2}\), during pyrolysis, can cause the formation of oxidized (polar) chemical groups, which most probably can better interact with the polar parts (asphaltenes) of the bitumens. This would give stronger interactions with the bitumen. It can be argued that this can also give better distribution among the sample. Comparison with bitumens modified with CaCO\({}_{3}\) is interesting. CaCO\({}_{3}\) is used in many works on bitumen and asphalt concretes as a standard inert filler. Addition of CaCO\({}_{3}\) at 3 wt% to bitumen gives a 4 \({}^{\circ}\)C increment in T* and a three-fold increase in G\({}^{\prime}\)@50 \({}^{\circ}\)C [34]. Interestingly, the addition of our chars gives a not-significant effect in T* (increase of about 3.5-4 \({}^{\circ}\)C) but a markedly higher effect in G\({}^{\prime}\)@50 \({}^{\circ}\)C (about seven times higher). It can be concluded that our char gives an enhanced effect in increasing the rigidity at working conditions. It is interesting to note that the two quantities are generally correlated, as clearly visible in the correlation plot of Figure 4C. It must be pointed out that G\({}^{\prime}\)@50 \({}^{\circ}\)C refers to the Y-value of the G\({}^{\prime}\) plot in Figure 4A, and T* refers to the X-value at which the curve drops in the same plot, so they are two independent parameters. The fact that they both give the same information means that they can be safely considered as self-consistent indicators of the effects exerted by char. The data in Figure 4C are compared with literature data (bitumens reinforced with organic molecules [35] shown by brown crosses, cellulose [36] shown by vertical green bars and inorganic fine particles [37] shown by horizontal blue bars). Clearly, all the data share the same behavior, suggesting universal behavior. Upon deeper observation, it can be noted that the data of this manuscript are slightly above the others, confirming that the char under investigation causes a marked effect on G\({}^{\prime}\)@50 \({}^{\circ}\)C. The fact that the proposed chars cause a bigger effect on the increase in G\({}^{\prime}\)@50 \({}^{\circ}\)C rather than in T* could be the consequence of the interactions between the char particles and the bituminous matrix being more effective at lower temperature, but they easily become less effective as the temperature is increased, thus ruling out particular effects when temperature approaches the transition temperature T*, where the effect is therefore not higher than that of any inert filler.