# Performance Evaluation of Steel Slag Asphal Mixtures for Sustainable Road Placement Rehabilitation
## 2 Materials and Methods  
### Materials and Specim Preparation  
Natural aggregates, SSA, mineral filler, and bituminous binder were used to produce the asphalt mixtures. The selected mixture type was--AC 20 base 35/50--an asphalt concrete for the base layer, with a maximum aggregate size of 20 mm and using as binder a bitumen with penetration class 35/50. The penetration class 35/50 was selected because this is the most used in Portuguese paving technology and other regions with similar climatic conditions. The same filler, from limestone origin, and paving grade bitumen were used throughout the study. In this manner, these materials were not a variable. The natural aggregate (NA) selected to produce the asphalt mixtures was obtained from crushed limestone rock produced by a local quarry. The SSA was obtained from a steel production plant. In this plant, SSA is generated by the electric arc furnace (EAF) and the factory production control is certified according to the requirements set by EN 13242:2002+A1:2007 [5]. Table 1 presents the mechanical and physical properties of the NA and SSA. In this study, the same fraction--0/20--was considered for both aggregates. The formulation of the asphalt mixture was done according to the Marshall method. The optimum binder content, 4.7%, was determined for the reference mixture (0% SSA) and then reproduced in the mixture with 20% SSA. Due to the high density of the SSA, maintaining the same binder content in % by mass of mixture would lead to a higher volumetric quantity of binder. Thus, for the mixture with 35% SSA was applied the same binder content in % by volume, equal to the mixture with 20% SSA. The composition of the asphalt mixtures is presented in Table 2. The SSA was used to replace 20% and 35% of the mass of NA. The aggregate particle size distribution of the asphalt mixtures is shown in Figure 1, where the dashed lines represent the grading envelope, lower and upper limits, according to the Portuguese specifications [32]. Figure 2a shows the particles of the aggregate dimension 0/20 of SSA. Figure 2b presents the fraction of SSA dimension 11.2/16.0. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Property** & **NA** & **SSA** \\ \hline Apparent particle density (Mg/m\({}^{3}\)) & 2.694 & 3.689 \\ Particle density on an oven-dried basis (Mg/m\({}^{3}\)) & 2.619 & 3.530 \\ Particle density on a saturated and surface-dried basis of & 2.647 & 3.573 \\ aggregate (Mg/m\({}^{3}\)) & 1.1 & 1.2 \\ Resistance to fragmentation by the Los Angeles test method (LA) & 30 & 25 \\ Methylene blue (g/kg) & 1.0 & 0.2 \\ Sand equivalent (SE) & 39 & 78 \\ Flakiness index (FI) & 11 & 1 \\ Shape index (SI) & 10 & 2 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Mechanical and physical properties of the aggregates. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Asphal Mixture** & **NA** & **SSA** & **Filler** & **Bitumen** \\ \hline
0\% SSA & 90.53 & 0.00 & 4.77 & 4.70 \\
20\% SSA & 71.47 & 19.06 & 4.77 & 4.70 \\
35\% SSA & 57.28 & 33.42 & 4.77 & 4.53 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Composition of the asphalt mixtures (% by mass). The asphalt mixtures were compacted into cylindrical and prismatic specimens according to the required by the mechanical test to be performed. Cylindrical specimens (with 100 mm of diameter and 63.5 mm of height) were compacted by the impact compactor, following EN 12697-30 [33], applying 50 blows on each face. Cylindrical specimens were produced for the Marshall and water sensitivity tests. Prismatic specimens were compacted using the roller-compactor as described by EN 12697-33 [34]. In the case of the permanent deformation test, the specimens had the dimensions 400 mm \(\times\) 300 mm \(\times\) 60 mm. In the case of the fatigue resistance test, the compacted specimens had the dimensions 400 mm \(\times\) 300 mm \(\times\) 50 mm and were subsequently sawed into specimens with dimensions 400 mm \(\times\) 50 mm \(\times\) 50 mm.