## 2 Experimental Materials and Methods
### Experimental Methods
#### 2.2.2 Experimental Procedure for Fracture Properties of Asphal Mixtures  
First, the asphalt mixture specimens were processed by 0, 3, 6, 9, 12, 15, 18, and 21 F-T cycles according to the previous studies [6; 7; 15; 16]. Before the F-T cycle processing, the specimens were sealed separately with a plastic bag, and then 15 mL of water was poured into each of the bags. Then, the test specimens were immediately put into the refrigerator. Each F-T cycle included freezing the test specimens in an -18 \({}^{\circ}\)C refrigerator for 16 h, and then thawing them in 25 \({}^{\circ}\)C water for 8 h.  
The uniaxial compression test is a commonly used experimental method for determining the compressive strength of bituminous mixtures, while the low temperature cracking test is a common and simple test method for assessing the crack resistance of bituminous mixtures at low temperatures. For the purpose of further investigating the influence of the F-T cycles on the damage of the SMA-13 asphalt mixture specimens, the AE technology was also used during the high-temperature uniaxial compression and low-temperature splitting tests. For the AE test, a few AE parameters were measured from the AE signals. On the basis of these parameters, the AE signal characteristics of the SBS-modified asphalt mixtures that were reinforced with basalt fiber tested during the compression or splitting test were used to characterize their damage mechanisms. (1) High-Temperature Uniaxial Compression Test  
In this paper, an electro-hydraulic servo pressure material testing machine (Jinli Test Technology Co., Ltd., China) was selected to perform the uniaxial compression test at 50 \({}^{\circ}\)C for basalt fiber-modified asphalt mixtures subjected to F-T cycles. Figure 3 illustrates the scene of the uniaxial compression test combined with the AE test. The testing system included a loading control system, a data acquisition and processing system, an environmental chamber, and so on. The AE system with six channels consisted of one AE sensor attached on the asphalt mixture specimen with a kind of sound-transmitting coupling agent, preamplifier, as well as an acquisition and data analysis system. For the purpose of obtaining the stress-strain relationship curve of the asphalt mixture specimens, the displacement control during compression was used for loading at a constant strain rate. Before the tests, asphalt mixture specimens were kept in an environmental chamber at 50 \(\pm\) 0.5 \({}^{\circ}\)C for more than 4 h to ensure uniform temperature distribution inside the specimens, and the test loading rate was set to 1 mm/min. Following the specification JTG E20-2011 [34], the compressive strength, failure strain, and compression failure stiffness modulus were calculated using the following equations, respectively. \[R_{c}=4P_{c}/\pi d^{2}, \tag{1}\]  
\[\varepsilon_{c}=\Delta l/l, \tag{2}\]  
\[\mathrm{S_{c}}=\mathrm{R_{c}}/\varepsilon_{c}, \tag{3}\]  
where \(R_{c}\) is the compressive strength, \(P_{c}\) is the maximum force of the compression test, \(d\) is the diameter of the asphalt mixture specimen, \(\Delta l\) is the deformation in the compressive test, \(\varepsilon_{c}\) is the compressive failure strain, and \(S_{c}\) is the compression failure stiffness modulus. (2) Low-Temperature Splitting Test  
In this paper, an electro-hydraulic servo pressure material testing machine produced by the Jinli Test Technology Co., Ltd. was also selected to perform the low-temperature splitting test at -10 \({}^{\circ}\)C for the basalt fiber-modified asphalt mixtures subjected to repeated F-T cycles. Figure 4 shows the scene of the low-temperature splitting test combined with the AE test. Before the tests, the asphalt mixture specimens were kept in the environmental chamber at -10 \(\pm\) 0.5 \({}^{\circ}\)C for at least 6 h to ensure uniform temperature distribution inside the specimens. The displacement control was used for loading at a constant strain rate and the test loading rate was also set to 1 mm/min.