## 1 Introduction  
Researchers around the world have been using and developing the existing evaluation indexes of asphalt and asphalt mixtures [1; 2; 3] to evaluate their performance and better guide the design of the asphalt pavement. The softening point, penetration index, rheological properties of asphalt are adopted to evaluate the performance of asphalt material [4; 5; 6]. Moreover, the Marshall stability, four-point bending fatigue test, Semi-circle bending (SCB) test, etc. are used to assess the performance of the asphalt mixtures [7; 8; 9]. Basalt fiber is a kind of eco-friendly fiber made from basalt stone and it has good mechanical properties, stability, and thermal insulation, and so on [10; 11]. Therefore, many researchers have used basalt fibers in various kind of research fields. For instance, the magnesium phosphate cement, the concrete and the aerospace research field etc. [12; 13; 14]. [PERSON] et al. [12], mentioned that basalt fiber is a potential candidate in replacing the glass fiber and the steel fiber to reinforce the cementitious materials due to its low cost and superior tensile strength etc. [PERSON] et al. [13]. conducted studies about basalt fiber reinforced concrete, and the results show that basalt fiber has a good reinforcing effect on the concrete and the fiber content and length will influence the property of concrete. [PERSON] et al. [14]. studied an optimization method to cut basalt fiber into different shapes to be better used in various fields such as the aerospace and automotive field. Basalt fiber is also used in the road engineering research field. Basalt fiber reinforced asphalt mixtures are now very popular due to its good performance [15; 16; 17], such as the high and low temperature properties and the water stability etc. [PERSON] et al. [15]. found that basalt fiber could reinforce the splitting tensile strength etc. before and after the freeze-thaw cycles. [PERSON] et al. [16]. concluded that basalt fiber could improve the adaptability of the asphalt mixtures in low temperatures. [PERSON] et al. [17]. conducted researches about asphalt mixtures reinforced by basalt fiber, lignin fiber, and polyester fiber. Their results showed that basalt fiber could improve the high and low temperature properties of asphalt mixtures. The basalt fiber used in the basalt fiber reinforced asphalt mixtures are in the form of a bundle, consisting of hundreds of single basalt fibers with a diameter at micron level. There is no doubt that the bonding ability between the basalt fiber bundle and the asphalt mortar can well reflect the reinforcing effect of the basalt fibers in the asphalt mixtures. This is because the bonding ability will influence the effectiveness of the basalt fibers bearing some part of the inner stress [18] inside the asphalt mortar or mixtures. However, the existing tests are mainly about the performance of the asphalt or the asphalt mixtures, the test about the bonding ability between the basalt fiber bundle and the asphalt mortar is very limited. [PERSON] et al. adopted the water contact angle test, SEM test and the FTIR test to reveal the adhesion between basalt fiber and asphalt [19]. Yet, these tests cannot quantitatively reflect the bonding between the basalt fiber and asphalt material. Many other studies adopted the similar method to reveal the bonding between basalt fiber and asphalt or mixture. Generally, SEM was designed to see the distribution of basalt fiber inside the asphalt mixture, and this method could just explain the connection or bonding status between the basalt fiber and the asphalt and it was just a qualitative analysis of the bonding between basalt fiber and asphalt. FTIR test could reveal the chemical functional group of the surface of the basalt fiber and the chemical composition of asphalt, and FTIR test could also not get a quantification index about the bonding between them.