# Char from Pyrolysis of Waste Tires to Increase Bitumen Performances
## 3 Results and Discussion
### Bitumen Characterization  
Both the real (G\({}^{\prime}\)) and imaginary part (G\({}^{\prime\prime}\)) of the elastic modulus were measured through temperature-sweep measurements, implying the heating of the sample at a constant heating rate of 1 \({}^{\circ}\)C min\({}^{-1}\) and subjected to a shear deformation at a frequency of 1 Hz. A typical result is shown in Figure 4A, where the curve associated with the pristine bitumen is reported. It can be easily seen that G\({}^{\prime}\) is lower than G\({}^{\prime\prime}\) in the considered temperature range and for all samples. This highlights that the samples are characterized by a pseudoplastic fluid behavior. Interestingly, both G\({}^{\prime}\) and G\({}^{\prime\prime}\) monotonously decrease with temperature, suggesting that the samples are at values greater than their glass temperature, where G\({}^{\prime\prime}\) should have a maximum, and usually occurring below 0 \({}^{\circ}\)C [32]. Figure 3: (**A**) Pore size distributions and (**B**) cumulative pore volumes of the sample tested. \begin{table}
\begin{tabular}{l c c c c c c c} \hline \hline
**Sample** & **S\({}_{\mathrm{BET}}\)** & **V < 0.7 nm** & **0.7 nm < V < 2 nm** & **V\({}_{\mathrm{mic}}\)** & **V\({}_{\mathrm{mes}}\)** & **V\({}_{\mathrm{T}}\)** & **V\({}_{\mathrm{mic}}\)/V\({}_{\mathrm{T}}\)** \\  & **(m\({}^{2}\)/g)** & **(cm\({}^{3}\)/g)** & **(cm\({}^{3}\)/g)** & **(cm\({}^{3}\)/g)** & **(cm\({}^{3}\)/g)** & **(cm\({}^{3}\)/g)** & **(cm\({}^{3}\)/g)** & **(\%)** \\ \hline \multicolumn{8}{l}{\({}^{\circ}\)as is\({}^{\circ}\)-char} & - & - & - & - & - & - \\ \hline N\({}_{2}\)-char & 79 & 0.010 & 0.003 & 0.013 & 0.521 & 0.534 & 2 \\ \hline N\({}_{2}\)+CO\({}_{2}\)-char & 123 & 0.011 & 0.019 & 0.030 & 0.559 & 0.589 & 5 \\ \hline CO\({}_{2}\)-char & 174 & 0.027 & 0.024 & 0.051 & 0.521 & 0.572 & 9 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Sample textural properties calculated from the adsorption isotherms. The plot in Figure 4A also allows the derivation of the G\({}^{\prime}\) value at 50 \({}^{\circ}\)C (G\({}^{\prime}\)@50 \({}^{\circ}\)C). This parameter is taken to represent the material's rigidity at working conditions (50 \({}^{\circ}\)C), in line with recently published research [33]. Upon a temperature increase, all samples become softer: at temperatures high enough, G\({}^{\prime}\) suddenly drops, indicating the gel-to-sol transition. The graphical derivation of this transition temperature (T\({}^{\bullet}\)) is shown in Figure 4A. From the physical chemistry point of view, T\({}^{\bullet}\) marks the situation where the molecular relaxation rate, obviously depending on the molecular thermal agitation, becomes sufficiently high for the system to accommodate the perturbation given through the mechanical distortion. In this situation, purely flowing behavior is shown, with vanishing of any elastic storage of mechanical energy (G\({}^{\prime}\) = 0). G\({}^{\prime}\)@50 \({}^{\circ}\)C and T\({}^{\bullet}\) values are shown in Figure 4B as a function of added char (wt%). The values shown give some interesting information. The addition of char causes an increase in both G\({}^{\prime}\)@50 \({}^{\circ}\)C and T\({}^{\bullet}\). This is quite a well-known effect: the presence of fine particles causes the reinforcement of the structure formed by the molecules in bitumen. This is basically due to interactions between the bituminous molecules and the particles' surface. In this way, a network formed by alternate...bitumen-particle-bitumen-particle... is made with an overall effect to reinforce the overall structure. In this sense, and this is the scientific idea at the basis of the present work, organic-based particles like those of char can offer an organic-based surface for effective interactions with bituminous molecules. This chemical compatibility is expected to allow (i) better accommodation of the carbon-based particles within the bituminous matrix and (ii) effective interactions with the molecules of bitumen and a more marked effect of the hosted char.