# Polysaccharides-Reinforced Bitumens: Specificities and Universality of Rheological Behavior
## 3 Results and Discussion
### \(G^{\prime}\)@50 \({}^{\circ}\)C and T\({}^{\star}\)  
First of all, the value of \(G^{\prime}\) at 50\({}^{\circ}\)C (\(G^{\prime}\)@50 \({}^{\circ}\)C) can be immediately derived and is representative of the mechanical property (rigidity) of the material. The temperature of 50 \({}^{\circ}\)C was chosen as representative of the normal temperature under usage conditions. On the other hand, the idea of considering the rigidity at temperatures higher than room temperature is sometimes adopted in the literature so the use of \(G^{\prime}\) at 50 \({}^{\circ}\)C in the present work allows comparison with those papers [18]. The value of \(G^{\prime}\)@50 \({}^{\circ}\)C is expected to change in the presence of additives as a consequence of the additive (reinforcing) effect on the bitumen microstructure. The effect of temperature is reported in Figure 1 where the behavior of \(G^{\prime}\) and \(G^{\prime}\) as a function of temperature is shown for the neat bitumen chosen as representative. When temperature is increased, the material becomes progressively softer with \(G^{\prime}\) monotonously decreasing. This fact, together with the fact that \(G^{\prime}<G^{\prime\prime}\) always holds, shows that the samples have a pseudoplastic fluid behavior and allows to consider that the investigated temperatures are all at higher values than the glass temperature, usually slightly below 0 \({}^{\circ}\)C [3], at which \(G^{\prime\prime}\) should have a maximum. Upon increasing temperature, at a certain point, \(G^{\prime}\) suddenly drops. The temperature at which \(G^{\prime}\) drops (T\({}^{\star}\)) is taken as that temperature at which \(G^{\prime\prime}\)/\(G^{\prime}>1000\). T\({}^{\star}\) has the meaning of being that temperature at which the binder can be considered almost as a Newtonian fluid. From the microscopic point of view, it can be intended as the temperature at which the thermal motion is sufficiently high to completely destroy the interacting network made by the above described complex structure. Consequently, at T\({}^{\star}\) no storage of energy can be afforded by the sample so the storage modulus \(G^{\prime}\) drops. The sudden drop of \(G^{\prime}\) is shown in the same Figure 1 together with the easy way to extract the  
Figure 1: Plot of \(G^{\prime}\) and \(G^{\prime\prime}\) as a function of temperature for a representative sample (neat bitumen). The meaning of the extracted values of \(G^{\prime}\)@50 \({}^{\circ}\)C and T\({}^{\star}\) is shown by the pointing arrows. From the values of \(G^{\prime}\) and \(G^{\prime\prime}\) around 50 \({}^{\circ}\)C the Arrhenius plot of \(\eta^{\star}\) is built and reported in the inset which also shows how to extract the activation energy (Ea). In the inset the red line is the linear regression of the experimental data (circles). corresponding T*. Like \(G^{\prime}\)@50 \({}^{\circ}\)C, and for the same reason, T* is also expected to change according to the additive added to the bitumen. The values of \(G^{\prime}\)@50 \({}^{\circ}\)C and T* are reported in Table 1 for the various samples. It is interesting to notice that the \(G^{\prime}\)@50 \({}^{\circ}\)C is correlated with T* as shown in Figure 2. The goodness of this result is supported by the observed R-squared value (0.985). Although this may be expectable, it must be noticed that \(G^{\prime}\)@50 \({}^{\circ}\)C refers to the Y-value of the \(G^{\prime}\) plot in Figure 1, whereas T* refers to the X-value at which the curve drops, i.e., two independent, in principle, parameters. The observed correlation therefore confirms that the reinforcing effect caused by the network-type interactions between the additive and the asphaltene clusters and their aggregates takes place at all temperatures shifting T* to higher values: this means that the rigidity at temperatures under usage conditions and the maximum possible operational temperatures can be seen as different aspects of the same microscopic phenomenon. This observation is in accordance with that observed by [PERSON] et al.