# Char from Pyrolysis of Waste Tires to Increase Bitumen Performances
## 3 Results and Discussion  
### Char Characterization  
All char samples possess millimeter and sub-millimeter particles. See Supporting Information (Figure S1) for a representative photograph. However, such particles are smaller particles that loosely aggregate and easily disassemble during handling. During the mixing and stirring of the char with hot bitumen to form the char-bitumen composite, they disassemble to give smaller particles. In fact, the final char-containing bitumen is quite homogeneous in texture, not containing such big mm-scaled (or sub-mm) particles. To estimate the size distribution of the \"individual\" particles, the CO\({}_{2}\)- and N\({}_{2}\)-chars were dispersed in silicone oil, the suspension sonicated in a commercial low-power sonicator and the final solution observed through optical microscopy. The soft sonication in silicone somehow simulates the char dispersion during the preparation of char-containing bitumens, where a suitable amount of char is stirred in hot bitumen. Chemically, silicone oil is apolar and reproduces the basic apolar characteristic of the bitumen [30], and its high viscosity at room temperature reproduces the viscosity of the bitumen at the high temperature (150 \({}^{\circ}\)C) employed during the mixing of the char with bitumen. In addition, sonication should somehow speed up char dispersion, in the same way as the stirring with hot bitumen does. Obviously, this treatment helps in disassembling the big char aggregates. It is just a way to simulate the bitumen preparation procedure. Microscopic investigation on the samples treated in this way just helps in understanding the size distribution of the individual char particles. Nevertheless, observing the real state of the char particles within the bitumen would need different and ad hoc techniques. The size distribution of both char samples after the disassembling of the aggregates in silicone oil is reported in Figure 1. It must first be noted that the particle sizes for both char samples mostly fall below the value range of 1-5 \(\upmu\)m with very few particles of a size \(>\)5 \(\upmu\)m. It can also be noted that CO\({}_{2}\)-char is more abundant in particles with a size below 1 \(\upmu\)m than N\({}_{2}\)-char. Contrarily, N\({}_{2}\)-char contains more particles with a size greater than 1.2 \(\upmu\)m compared to CO\({}_{2}\)-char. The N\({}_{2}\)-char size distribution is therefore shifted to slightly larger sizes compared to that of CO\({}_{2}\)-char. It is also broader, whereas the size distribution of CO\({}_{2}\)-char particles looks sharper. The particle size distributions for N\({}_{2}\)+CO\({}_{2}\)-char (not shown in the figure for clarity's sake) are in-between that of the N\({}_{2}\)-char and CO\({}_{2}\)-char. The general behavior that CO\({}_{2}\)-char particles are generally smaller than those of the N\({}_{2}\)-char suggests that the latter has a higher natural chemical tendency to form aggregates. The observed differences can be attributed to the oxidizing environment (CO\({}_{2}\)) that is more aggressive and reactive in the synthesis phase compared to an inert environment (N\({}_{2}\)). It is important to note that further experiments, performed with different dispersing solutions (see Supporting Information and Figures S2 and S3), gave similar results. These considerations are consistent with the N\({}_{2}\) adsorption experiments on the as-prepared (untreated) chars. The behavior of the char upon a temperature increase was investigated using Thermogravimetry. The results are shown in Figure S4 of Supporting Information. Basically, the data show that at about 500 \({}^{\circ}\)C, degradation takes place for all the chars. Interestingly, the degradation of the CO\({}_{2}\)-char is complete within just a hundred degrees, whereas it is much  
Figure 1: **Top panel**: CO\({}_{2}\)-char (**left**) and N\({}_{2}\)-char (**right panel**) dispersed in silicone oil (bar length equals 30 \(\upmu\)m).