# Fatigue Performance and Model of Polyacrylonitrile Fiber Reinforced Asphalt Mixture
## 3 Specimen Preparation and Test Procedure  
Three asphalt contents (OAC, OAC+0.5%, and OAC\(-\)0.5%) and four PAN fiber contents (0, 0.15%, 0.3%, and 0.45% by weight) were used in the experimental design. The mixture was compacted using a roller compactor following the Chinese Standard Test Methods of Bitumen and Bituminous Mixtures for Highway Engineering (JTG E20-2011) [25]. After compaction, the slabs were cut into flexural fatigue beam specimens with dimensions of 50 mm width, 50 mm height, and 250 mm length, as shown in Figure 3. At least three beams were prepared for every strain level. Air voids of flexural beams ranged between 7 \(\pm\) 1%. The fatigue tests shown in Figure 4 were performed by using a Mechanical Testing & Simulation (MTS) testing apparatus according to the Chinese Standard Test Methods of Bitumen and Bituminous Mixtures for Highway Engineering (JTG E20-2011) [25]. All fatigue tests were based on the strain-controlled mode of loading. A central-point load and a haversine-shaped wave at a frequency of 10 Hz were used in this study. The span of beam was 200 mm. All specimens were tested at 20 \({}^{\circ}\)C. Based on the ultimate flexural tensile-strain, five strain levels (600, 1000, 1500, 2000, and 2500 microstrain) were chosen for the mixture with fibers and four strain levels (600, 1000, 1200, and 1500 microstrain) were chosen for that without fibers. During the fatigue tests on the strain-controlled mode, the fracture of the flexural beam is not often observed obviously. Therefore, the fatigue life is defined as the number of repetition cycles when the stiffness of the mixture reaches half of its initial stiffness value, taken at the 50 th cycle. To minimize \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**PAN Fiber Content** & **OAC** & **Air Voids** & **VMA** & **VFA** & **Stability** & **Flow** \\
**by Weight (\%)** & **(\%)** & **(\%)** & **(\%)** & **(\%)** & **(\%)** & **(kN)** & **(0.1 mm)** \\ \hline
0 & 4.9 & 4.1 & 14.2 & 71.1 & 10.4 & 28.7 \\
0.15 & 5.0 & 3.9 & 13.9 & 71.9 & 12.7 & 32.1 \\
0.30 & 5.1 & 4.0 & 14.1 & 71.6 & 13.6 & 30.5 \\
0.45 & 5.3 & 4.2 & 14.1 & 70.2 & 14.2 & 35.9 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Results of all of AC-16 mixtures at the optimum asphalt content (OAC) based on the [PERSON] method. Figure 3: Beam-shaped specimens prepared for the fatigue test. Figure 5: Relationship between flexural strain and fatigue life (%AC is asphalt content in figure). (**a**) Without fiber; (**b**) 0.15% fiber content; (**c**) 0.30% fiber content; and (**d**) 0.45% fiber content. From Table 5 and Figures 5 and 6, it can be seen that the regression results have shown that the correlation coefficient, \(R^{2}\), of each regression equation determined by Equation (1) is quite high. This means that the regression equation fits well. Compared with the mixture with fiber or without, the average value of the fatigue parameter, \(k_{2}\), declined by about 25%. It is shown that the fatigue sensitivity to the strain decreased significantly after adding fiber into the mixture. The anti-fatigue ability improved significantly. A seen in Figure 6a, the fatigue performance of the mixture was also improved with the asphalt content increasing at the same fiber content. It also can be seen from Figure 7, in the condition of low strain, that the effect of the fiber content on the fatigue life is more obvious than that in the condition of high strain. Figure 6: _Cont._