## 2 Materials and Methods
### Active and Passive Adhesion  
The aggregate-bitumen interface significantly affects the moisture resistance of AM. This aspect has been evaluated in accordance with ASTM D3625 with varying percentages of filler [36]. Active adhesion is the time required to accurately coat the aggregate with bitumen during the mixing operation. Bitumen, filler, and aggregate were preheated at a temperature of 170 \({}^{\circ}\)C and then mixed with optimal proportions. The total time elapsed between the addition of the target binder content and 100% coating of the aggregate is measured in seconds [37]. The time required to completely coat the aggregate was noted and reported as active adhesion. The shorter elapsed time represents good active adhesion.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Property** & **OPC** & **SF** \\ \hline Specific gravity (g/cm\({}^{3}\)) & 3.04 & 2.2 \\ MBV (g/kg) & 3.00 & 3.85 \\ German filler (g) & 85 & 94 \\ Fineness modulus (FM) & 4.96 & 1.96 \\ Average particle size (\(\mu\)m) & 10.12 & 0.243 \\ Surface area (m\({}^{2}\)/g) & 1.75 & 16.45 \\ pH & 12.90 & 6.98 \\ Loss on ignition (\%) & 1.8 & 2.0 \\ Particle shape & Granules and sub-angular particles with rough texture & Spherically shaped and very fine \\ Mineralogical composition (XRD) & Alite, Belite, Calcite, Quartz, Portlandite & Quartz and Calcite \\ SiO\({}_{2}\) (\%) & 21.43 & 93.5 \\ CaO (\%) & 66.58 & 0.89 \\ Al\({}_{2}\)O\({}_{3}\) (\%) & 3.01 & 0.08 \\ MgO (\%) & 1.39 & 0.82 \\ SO\({}_{3}\) (\%) & 2.26 & - \\ Na\({}_{2}\)O (\%) & 0.03 & 0.4 \\ K\({}_{2}\)O (\%) & 0.02 & 3.52 \\ TiO\({}_{2}\) (\%) & 0.21 & - \\ MnO (\%) & 0.20 & 0.06 \\ Fe\({}_{2}\)O\({}_{3}\) (\%) & 4.68 & - \\ TiO\({}_{2}\) (\%) & - & 0.05 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Properties of fillers.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline  & \multicolumn{3}{c}{**Passing Percentage (\%)**} \\ \cline{2-4}
**Sieve Size** & \multicolumn{2}{c}{**MoRTH**} & \multicolumn{1}{c}{**MoRTH**} & \multicolumn{1}{c}{**Considered**} \\  & **Upper Limit** & **Lower Limit** & **Silica Fume** \\ \hline
0.6 mm & 100 & 100 & 100 \\
0.3 mm & 100 & 95 & 96.8 \\
0.075 mm & 100 & 85 & 90.3 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Grain size curve of silica fume as per MoRTH requirement for filler material.  
Passive adhesion was calculated by visual inspection using the boiling water test according to ASTM D 3625-96. The passive adhesion was determined through visual inspection. A 250 g AM was prepared and stored at room temperature to cool the mixture down to a temperature of 85-100 \({}^{\circ}\)C. The cooled bitumen aggregate mixture is boiled in water for 10 min and after boiling it is cooled again to room temperature. The water is decanted from the boiled mix and then dried on absorbent paper after boiling the aggregate-bitumen mix for 10 min. The percentage of bitumen that remained spread on the aggregate was reported as passive adhesion. The percentage of bitumen that remained coated on the aggregate was studied by a team of 5 technicians using a magnifying glass. The average value obtained for the percentage of bitumen remain coated on aggregates is reported as passive adhesion.  
The results of passive and active adhesion are presented in Figure 2. Results show a better active and passive adhesion of silica fume with respect to OPC, which should ensure higher moisture damage resistance to SF bituminous mixes.