# Char from Pyrolysis of Waste Tires to Increase Bitumen Performances
## 2 Experimental Section  
The waste-tire-derived powdered rubber was supplied by Ecopneus s.c.p.a. It is a black powder with 0.4-0.8-mm-sized grains obtained in a laboratory through particle sieving from tire fragments of a broader size distribution. The powder was washed with toluene and drying was carried out in an oven with the temperature set at 135 \({}^{\circ}\)C. The results of proximate and ultimate analyses on waste tires are reported in Table 1. The analysis shows the high carbon content typically expected for such a type of a material. It must be pointed out, in light of environmental attention, that they are classified as waste with CER 16 01 03, so they need to be treated according to the specific legislation. The bitumen used for the purpose of this study was supplied by Lo Prete (Reggio Calabria, Italy) although the origin of the bitumen is Saudi Arabia. The characteristics of the bitumen have been determined in previous investigations [19]. Briefly, (i) the bitumen has a crossover temperature, i.e., the temperature at which the bitumen passes from a glassy elastic solid (G\({}^{\prime}\) > G\({}^{\prime\prime}\)) to a viscoelastic liquid (G\({}^{\prime}\) < G\({}^{\prime\prime}\)), of 7.8 \({}^{\circ}\)C; (ii) the penetration grade of the bitumen is 50/70 as measured through the standard procedure [20] of a standard needle being loaded with a weight of 100 g and then measuring the length traveled into the bitumen specimen in tenths of a millimeter for a known time, at a fixed temperature. The penetration grade of a bitumen is expected to decrease as an effect of particle addition [21] (see, later, discussion of the results). Pyrolysis was carried out using an electric furnace with a sample holder in the form of a cylindrical stainless-steel reactor with a length of 15 cm and an internal diameter of 5 cm. The reactor linked to the 1/4-inch pipeline allows the influx/efflux of gas through a Mass Flow Controller. The set parameters of the procedure such as temperature, gas flow and heating rate were monitored regularly in real time using homemade software developed via the LabView version 8.2 system (National Instrument data acquisition system) [22]. The samples (about 16 g for each run cycle) were placed in the stainless-steel reactor and heated up to 900 \({}^{\circ}\)C. The pyrolysis/activation test lasted approximately 6 h. These conditions were chosen after preliminary thermogravimetric tests and follow the general trend of pyrolysis of different raw materials. All samples (char) were obtained through pyrolysis/activation of waste tires under nitrogen and carbon dioxide constant flow rates to establish an inert/oxidant atmosphere inside the chamber. Different samples were obtained by changing synthesis parameters as reported in Table 2. The final char (yield between 30 and 40%) was recovered from the reactor at the end of the experimental test. All of them were collected when the reactor reached room temperature. All samples were synthetized by using the same synthesis parameters except for the gas specimen, according to the synthesis parameters reported in Table 2.  
Bitumen reinforcement by char was carried out as follows: char was added in three varying proportions (1, 3, 6% wt/wt) to bitumen, which was in its liquid flowing state at a temperature of 150 \(\pm\) 10 \({}^{\circ}\)C. Homogenization of the mixture was carried out at the same temperature using a mechanical stirrer (IKA RW20, Konigswinter, Germany) set to 500-700 rpm for 30 min. Rotation rates at a lower rpm are not effective in obtaining homogeneous samples, whereas if rotation rates are higher than 700 rpm, the bitumen could begin to undergo oxidation due to the increase in the bitumen-air interface in the vortex, which forms during stirring, and presumably also due to the obvious increased interfacial kinetics. For these reasons, this method is regarded as a usual procedure, as