# Mechanical Performance of Gilsonite Modified Asphalt Mixture Containing Recycled Concrete Aggregate
## 2 Materials and Methods
### Mix Design Procedure  
In this research, six types of mixes were designed and tested, which are described as follows:  
* The MDC-19 and MDC-25 mixes were the control. These used AC 60-70 as a binder and 100% of their aggregates were NA. The gradation of these mixes is presented in Figure 2.
* The MDC-19-M and MDC-19-V mixes had the gradation of the MDC-19 mix; however, they used AC/G/10% as a binder and replaced 21% (particles retained in sieve 3/8\" or 9.5 mm) of the NA with RCA. M or V indicate that the replacement was carried out by mass or volume, respectively. * The MDC-25-M and MDC-25-V mixes had the gradation of the MDC-25 mix; however, they used AC/G/10% as a binder and replaced 24% (particles retained in sieve 1/2\" or 12.5 mm) of the NA aggregate with RCA. Considering that the gradation of RCA presented more than 90% of the material that was retained in a 3/8\" sieve (9.5 mm), a replacement of 21% and 24% of the mass of NA with RCA was chosen for MDC-19-M and MDC-25-M, respectively. In other words, harnessing RCA was greater when replacing the coarse fraction of NA. Replacing this with particles of a smaller size would increase the costs, entailing an industrial process. \begin{table}
\begin{tabular}{l c c c} \hline \hline
**Test** & **Method** & **NA** & **RCA** \\ \hline Specific gravity/absorption—coarse & AASHTO T 84 & 2.65/1.8\% & 2.52/4.9\% \\ Specific gravity/absorption—fine & AASHTO T 85 & 2.53/1.5\% & 2.48/5.2\% \\ Los Angeles Machine, 500 & AASHTO T 96 & 22.7\% & 31.1\% \\ revolutions & & & \\ Micro-deval & AASHTO T327 & 21.1\% & 29.0\% \\ Fractured particles: 1 face & ASTM D 5821 & 87.6\% & 97.2\% \\ Plasticity index & ASTM D 4318 & No plastic & No plastic \\ Flattening index & & 6.5\% & 3.0\% \\ Elongation index & & 8.2\% & 2.2\% \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Properties of NA and RCA particles. \begin{table}
\begin{tabular}{l c c c} \hline \hline
**Test** & **Method** & **Unit** & **Value** \\ \hline \multicolumn{4}{c}{**Tests on the original AC**} \\ \hline Penetration (25 \({}^{\circ}\)C, 100 g, 5 s) & ASTM D-5 & 0.1 mm & 42.0 \\ Softening point & ASTM D-36-95 & \({}^{\circ}\)C & 75.6 \\ Specific gravity & AASHTO T 228-04 & - & 1.014 \\ Viscosity to 135 \({}^{\circ}\)C & AASHTO T-316 & Pa-s & 1.02 \\ \hline \multicolumn{4}{c}{**Tests on the residue of AC after the RTFOT**} \\ \hline Mass loss & ASTM D-2872 & \% & 0.44 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Properties of AC/G/10%. Additionally, particle sizes corresponding to the superior sieves were chosen on each mix to carry out the replacements (1/2'' + 3/8'' on MDC-19 and 3/4'' + 1/2'' on MDC-25). In order to make the replacements according to volume for mixes MDC-19-V and MDC-25-V, the specific gravities of both aggregates (NA and RCA) were taken into consideration, and the guidelines recommended by the authors of [80] were followed. The method used to design and obtain the optimal asphalt content (OAC) of mixes was the Marshall method. For this reason, the manufactured samples were Marshall type (cylindric samples compacted at 75 blows per face, with an approximate mass of 1200 g, and with approximate dimensions of 63.5 mm in diameter and 101.6 mm in height). Additionally, the recommendations of the AASHTO T-245 general guidelines were followed, and all mixes were manufactured under short-term oven aging (STOA) conditions following the protocols recommended by AASHTO R30 (before compacting samples, these were heated in a loose state for 2 h inside a conventional oven at 135 \({}^{\circ}\)C). The compaction and mix temperature for the control mixes (MDC-19 and MDC-25) were 150 \({}^{\circ}\)C and 145 \({}^{\circ}\)C, respectively. These temperatures were chosen based on the viscosity vs. temperature curve obtained for AC 60-70 (viscosity of 170 \(\pm\) 20 MPa-s for the mix temperature and 280 \(\pm\) 30 MPa-s for compaction). For the other mixes, which used AC/G/10%, said temperatures were 165 \({}^{\circ}\)C and 160 \({}^{\circ}\)C, respectively.