## 3 Results Analysis and Discussion
### Low-Temperature Bending Test Results and Analysis  
A three-point bending test was conducted at -10 \({}^{\circ}\)C to evaluate the anti-cracking performance of asphalt mixes. The bending strength and failure strain of four kinds of asphalt mix are shown in Figures 5 and 6, respectively. The addition of lignin fiber significantly improved the bending strength and tensile strain of asphalt mixes by about 19.9% and 28.7%, respectively, in comparison to the control mix. Meanwhile, the bending strength and tensile strain of asphalt mix modified with diatomic were slightly increased by 7.9% and 13.6%, respectively, compared to that of the control mix. The composite asphalt mixes of diatomic and lignin fiber (DLFMAM) recorded the highest enhancement in the bending strength and tensile strain by 24.23% and 36.8%, respectively, with respect to the values of control mix. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Asphalt Mix ID**} & \multicolumn{2}{c}{**Low-Temperature Cracking Test**} & \multicolumn{2}{c}{**Marshall Immersion Test**} & \multicolumn{2}{c}{**Freeze-Thaw Splitting Test**} \\  & **Stress** & **Strain** & **MS\({}_{1}\)** & **MS\({}_{2}\)** & **MSR** & **RT\({}_{1}\)** & **RT\({}_{2}\)** & **TSR** \\  & **(Mpa)** & **(10\({}^{\circ}\)**t)** & **(KN)** & **(KN)** & **(\%)** & **(Mpa)** & **(Mpa)** & **(\%)** \\ \hline CAM & 7.51 & 2018.4 & 10.95 & 9.09 & 83.0 & 0.711 & 0.553 & 77.77 \\ LFMAM & 9.02 & 2589.12 & 11.02 & 9.93 & 90.11 & 0.738 & 0.593 & 80.35 \\ DMAM & 8.11 & 2294 & 11.71 & 10.79 & 92.14 & 0.748 & 0.627 & 83.82 \\ LFDMAM & 9.33 & 2762 & 12.11 & 11.51 & 95.05 & 0.773 & 0.659 & 85.25 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Experimental results of different asphalt mixes. The above results can be addressed with a certain mechanism. The asphalt binder filled among aggregates plays a major role in bonding when the temperature drops, so the asphalt mix does not crack easily. However, when the temperature is dropped to a certain extent, the base asphalt binder becomes unable to resist the extreme tensile stress, and cracks appear. If these cracks expanded it would be risky on the pavement service life and pavement strength. Lignin fiber can improve the cracking resistance of asphalt mixes, where it has a high specific surface area through which more amounts of asphalt  
Figure 5: Bending strength of asphalt mixes. Figure 6: Ultimate bending strain of asphalt mixes. components can be easily absorbed. The greater the absorption of asphalt binder, the greater the viscosity of asphalt, which enhances the interface adhesion strengths. Furthermore, the asphalt content absorbed by lignin fiber increases the flexibility of asphalt mixes since more asphalt films are formed to better perform the filling and healing functions in the micro-cracks among aggregates. Additionally, as shown in Figure 7, the three-dimensional lignin fiber is uniformly distributed in the asphalt mix. Therefore, after it is added to the asphalt mix, the bridging phenomenon happens among the asphalt mix components. The lignin fibers which go through both sides of the crack surface grow a bridge shape which can delay more asphalt cracking. Therefore, the toughness of lignin fiber can improve the anti-cracking performance, redistribute the stress in asphalt mix, and decrease crack spread rates in the asphalt pavement structure. On the other hand, diatomic has a small influence on the enhancement of low-temperature performance. That is to say, diatomic tends to improve the hardness of asphalt, which may improve the mechanical properties and the cracking resistance of mix to a certain extent. After that, the low-temperature cracking may appear. Nevertheless, diatomic powder, unlike the fibers, has no cross-linking with asphalt to act as bridges to hold asphalts and transfer stress once cracking appears.