# Evaluation of _Jatropha curcas_ and Pistachio Shell Particles as Modifier for Asphalt Binder
## 3 Results and Discussion
### Thermal Properties  
Figure 7 shows the Thermogravimetric Analysis (TGA) thermograms for asphalt, _Jatropha curcas_ particles, and _Jatropha_-modified asphalts. The _Jatropha_ shows two main steps of decomposition, first around 290 \({}^{\circ}\)C and the second at 335 \({}^{\circ}\)C; these correspond to cellulosic materials and lignin compounds, respectively [32]. The asphalt blends modified by _Jatropha_ shell presented one weight loss step in the temperature range from 250 \({}^{\circ}\)C to 500 \({}^{\circ}\)C, with a residue represented near 20 wt.%. The thermal degradation of resins, aromatics, and some asphaltenes has previously been reported in the same temperature interval [4]. The thermograms of modified asphalt blends with _Jatropha_ seed shells are shown in Figure 7. The incorporation of modifiers to the binder reduces its thermal decomposition susceptibility, as especially shown by the J4 sample. The asphalt blends modified with 2, 6, and 8 wt.% behave similarly so that the concentration of 4 wt.% _Jatropha_ particles is the critical value for achieving better thermal stability. The shift to high temperatures observed in the J4 thermogram could be a consequence of the interactions between the polar compounds of the _Jatropha_ seed shells and the polar fractions of the  
Figure 5: Isochronal plots of tan \(\delta\) vs. temperature at 10 rad/s of asphalt modified by _Jatropha curcas_ seed shell particles.  
Figure 6: Isochronal plots of tan \(\delta\) vs. temperature at 10 rad/s of asphalt modified by pistachio seed shell particles.  
asphalt, which establish forces that prevent the thermal rupture of bonds at relatively lower temperatures. Similar results were reported by [PERSON] et al. 2020 [33], who reported that more than 6% of waste pig fat improved the thermal stability, which was attributed to the high unsaturated fatty acid content that made the asphalt binder more susceptible to an insignificant thermal decomposition.  
The thermograms of pistachio-modified asphalt blends with pistachio shells are presented in Figure 8. Pistachio and _Jatropha_ show twomain decomposition steps: the first around 270 \({}^{\circ}\)C and second around 350 \({}^{\circ}\)C; however, the first is more significant compared with _Jatropha_ and at a lower temperature; those steps are attributed to hemicellulose and cellulose decomposition for the first and lignin for the second [34].The P2, P4, and P6 samples behave quite similarly and exhibit less susceptibility to suffering from thermal decomposition than the unmodified binder. On the other hand, the P8-sample thermogram overlaps that of the pure asphalt, which indicates that at elevated concentrations of pistachio shell particles, the modifier provides excessive amounts of light components that cause the adverse effect on thermal susceptibility of the modified asphalt blend. However, as previously discussed, this effect was not observed in the _Jatropha_-modified asphalt samples due to the more predominant lignin presence in _Jatropha_ compared with pistachio shells. Since lignin is a biopolymer of elevated molecular weight and high degradation temperature [5], the thermal stability of _Jatropha_-modified asphalts is improved more significantly than their corresponding samples modified by pistachio shells. However, the thermograms in Figure 8 still exhibit that pistachio shell particles reduce the degradation susceptibility of the asphalt binder by a maximum concentration of 6 wt.%.  
Figure 7: TGA thermograms of asphalt, _Jatropha curcas_, and modified asphalt mix with _Jatropha curcas_ seed shells.