## 3 Aggregate-Bitumen Interface Bond Strength Test  
### Test Equipment  
The role of asphalt binder in asphalt mixtures is to coat the stones and polymerize the stones together. Therefore, the adhesion theory has long been applied to evaluate the bond strength of hot  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Technical** & **Water** & **BET (m\({}^{2}\)/g)** & **Average** & **PH Value** & **SiO\({}_{2}\) Content (\%)** \\ \hline Test results & Hydrophobia & 125 \(\pm\) 20 & 12 & 5.0–8.0 & \(\geq\)99.8 \\ Standard values & — & 130 \(\pm\) 30 & \(\leq\)20 & 3.7–6.5 & \(\geq\)99.8 \\ Test procedure & GB/T20020 & GB/T20020 & GB/T20020 & GB/T20020 & GB/T20020 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Technical parameters of nano hydrophobic silane silica.  
Figure 1: Grafting process of silane coupling agent on nanosilica.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Technical** & \multicolumn{2}{c}{**Penetration**} & **10 \({}^{\circ}\)C** & **Softening** & **PI Value** & **135 \({}^{\circ}\)C Rotational** \\
**Parameters** & **15 \({}^{\circ}\)C** & **25 \({}^{\circ}\)C** & **30 \({}^{\circ}\)C** & **Ductility** & **Point** & **VI Value** & **Viscosity** \\ \hline Units & & 0.1 mm & mm & \({}^{\circ}\)C & - & mpa \\ Test results & 20.8 & 64.1 & 115 & 233 & 48.1 & \(-\)1.357 & 912.1 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Technical parameters of nano hydrophobic silane silica modified asphalt (NHSSMA).  
mix asphalt mixture (HMA). In the adhesion theory, the bond between aggregate and asphalt binder can be ideally considered as an adhesive joint. If more specific, it can be considered as a butt joint. In asphalt mixture system, the asphalt binder is an adherent and the aggregate is considered to be the bonded portion. The destruction of the system occurred within the binder or binder-filler mastic called cohesive failure, which occurred at the binder-aggregate interface considered as adhesive failure, and two failure modes are shown in Figure 2.  
In this paper, cohesive failure and adhesive failure are collectively referred to as bond failure. In order to measure the aggregate-bitumen interface bond strength of BA and NHSSMA, an aggregate-bitumen interface bond strength tester was designed independently, as show in Figure 3.  
Figure 3: Aggregate-bitumen interface bond strength tester.  
Figure 2: Adhesive failure and cohesive failure at the aggregate-bitumen interface.  
The aggregate-bitumen interface bond strength tester is mainly composed of nine main components, which are (1) upper separator, (2) lower separator, (3) hinged bar chain, (4) upper grip finger, (5) screw rod, (6) lower grip finger, (7) asynchronous motor, (8) pedestal and (9) data transmission line. The screw rod (5) of the tester can be driven by the asynchronous motor (7) to shear or stretch the test sample fixed between the upper grip finger (4) and lower grip finger (6). The test sample is clamped into the upper grip finger (4) and lower grip finger (6), computer can set the shear (tensile) rate, and the shear or tensile failure load is collected through the data line (9). The shear (tensile) rate was selected to be 1 mm/min. The aggregate-bitumen interface shear (tensile) strength can be calculated as following.  
\[SS=\frac{F_{s}}{S_{sc}},TS=\frac{F_{T}}{S_{Tc}},\]  
where \(F_{s}\) and \(F_{T}\) is the maximum shear and tensile failure load, \(S_{sc}\) and \(S_{Tc}\) is the shear and tensile failure area, and \(SS\) and \(TS\) is the aggregate-bitumen interface shear and tensile strength. The upper grip finger (4) is fixed on the lower separator (2) through the hinged bar chain (3), so that there is only a vertical upward tensile (shear) force during the tensile (shear) process, and no bending moment occurs. The self-developed aggregate-bitumen interface bond strength tester overcomes the disadvantage that the bending moment is easy to generate during the shear or tensile process in the conventional test equipment.