## Materials and Methods  
### Materials  
A conventional dense asphalt mixture AC20 35/50 (EN 13108-1:2007) was the mixture type selected to conduct the experimental study. The mixture particle size distribution is presented in Table 1. Limestone aggregates, limestone filler, and 35/50 conventional bitumen were the materials chosen for the production of the mixtures. According to the bitumen specification, the temperatures of 165 \({}^{\circ}\)C and 155 \({}^{\circ}\)C were adopted for the asphalt mixture production and compaction, respectively. The bitumen content, 4.7% by total weight of the mixture, was previously determined using the Marshall method. The mixing process was conducted using a laboratory mixer (EN 12697-35:2016). Cylindrical specimensof 100 mm in diameter and approximately 63.5 mm in height were compacted using a Marshall hammer (EN 12697-30:2004) applying 75 blows on each side of the specimen.  
Six types of asphalt mixtures were produced in this study: one conventional reference mixture (with no additives), two mixtures with graphene (with 1% and 2% dosage by mass of modified binder) and three mixtures with EAF slag (with 3%, 6% and 9% of aggregate replacement).  
Graphene nanoplatelets, commercially designated as GRAPHENIT-XL, were used to make the asphalt mixtures susceptible to microwaves. Regarding its chemical composition, graphene is essentially carbon (96.41%) with traces of other elements, such as oxygen (1.05%), sulphur (0.48%), nitrogen (0.48%), hydrogen (0.07%) and others. The graphene presents a bulk density of 0.04 g/cm\({}^{3}\). Similarly to other nanomaterials, the nanoscale of the graphene platelets enables a high specific surface area, thus occupying considerably more volume than conventional macroscopic particles. Figure 1 presents a sample of 2.50 g of graphene nanoplatelets and, by the left side, for comparison, 2.50 g of conventional limestone filler (fraction passing sieve 0.063 mm).  
The Graphene nanoplatelets were dispersed in the bitumen matrix by adding the nanomaterial to the bitumen heated at 160 \({}^{\circ}\)C and applying high-speed mechanical stirring (2000 rpm) during 60 min. Additional details about the mixing process can be found elsewhere [51]. After each bitumen modification (with 1% and 2% graphene), the asphalt mixtures were produced and compacted as described for the conventional mixture.  
The EAF slag used in this study is produced in Spain, and its chemical composition is reported in Table 2. After the hydration process carried out by the producer, the free calcium oxide becomes almost zero. This procedure prevents expansion problems associated with the presence of CaO. Two fractions of slag were used as a replacement of limestone aggregates, 0.5/2 mm and 0.063/0.5 mm. Figure 2 presents a sample of 50 g of both fractions. Although many investigations report that the substitution of coarse aggregates improves the mechanical properties of the mixture [45], in this research only fine aggregates were replaced, because this provides more homogeneous heating throughout the mixture,  
\begin{table}
\begin{tabular}{c c} \hline
**Sieve (mm)** & **\% Passing** \\ \hline
22 & 100 \\
16 & 83 \\
8 & 56 \\
4 & 42 \\
2 & 34 \\
0.5 & 19 \\
0.063 & 5 \\ \hline \end{tabular}
\end{table}
Table 1: Grading curve of the asphalt mixtures.  
Figure 1: Mass of 2.50 g of limestone filler under 0.063 mm (**left**) and graphene nanoplatelets (**right**).  
as reported by other authors [52]. Volumetric replacement principle was used in order to take into account the different bulk density of slag and natural aggregates [45].