# Influence of Fiber Mixing Process on the Cracking Resistance of Cold Recycled Asphal Mixture
## 1 Introduction  
Cold recycled asphalt mixture (CRAM) is one of the most promising technologies to reduce carbon emissions in road construction due to many advantages, such as lower greenhouse gas emissions, economic cost effectiveness, and better working conditions for construction workers [1]. However, the performance of CRAM is not as good as that of traditional hot mix asphalt mixture [2]. In particular, it is very sensitive to cold climates or freeze-thaw environments due to its poor cracking resistance, insufficient early strength, and poor fatigue durability [3, 4]. As a result, CRAM is generally used in the lower layersof pavement structures, such as base course or underlayer of asphalt pavements [5]. It is necessary to take effective measures to enhance the performance of CRAM, so that it can be used in the place of hot mixture asphalt (HMA) under a certain condition. Currently, fibers have been widely used to enhance the engineering properties because of its good reinforcement and toughening effect [6; 7; 8; 9; 10; 11; 12]. Specifically, fiber reinforcement improves fatigue life and retards rutting by increasing resistance to cracking and permanent deformation [13]. [PERSON] et al. [14] explored the effect of four kinds of fibers on the mechanical properties of CRAM, and the results showed that basalt fibers had the most significant improvement on the fatigue properties. [PERSON] et al. [15] found that polypropylene fibers could improve the bearing capacity and water damage resistance of emulsified asphalt mixture. Research conducted by [PERSON] et al. [16] reported that basalt fibers had an obvious effect on the splitting strength of asphalt mixture under low temperature conditions, and the reinforcing effect of fiber obviously played an important role in preventing cracks. [PERSON] et al. [17] also confirmed that basalt fibers delayed the expansion of micro cracks of emulsified asphalt mixture. Nevertheless, [PERSON] et al. [18] concluded that the addition of basalt fibers reduced the low temperature cracking resistance of CRAM. The reason for this phenomenon may be due to something wrong with the mixing process and the dosage of fiber in CRAM. The mixing process of the fibers directly affects the dispersion state of the fibers in CRAM, which determines the properties of CRAM to a certain extent. The research on fiber mixing processes may give a reasonable explanation for this phenomenon. In addition, the fiber content and modification mechanisms of CRAM also received great attention. [PERSON] et al. [19] studied the effect of fiber content on the road performance of CRAM. It was found that various road performance indicators such as dynamic stability, flexural-tensile strain, and the freeze-thaw splitting strength of CRAM first increased and then decreased with the increase of fiber content. Therefore, it is very important to select the appropriate dosage of fibers for CRAM to meet the performance requirement of different service environments. Furthermore, scanning electron microscopy (SEM) has also been proven to be an effective means for the research of fiber modification mechanisms. It can be observed that fibers enhanced the integrity of CRAM through interfacial reinforcement [20]. Thus, the objective of this study is to evaluate of the influence of fiber mixing process on the cracking resistance of CRAM from multiple perspectives. To achieve this goal, four fiber mixing processes were designed by changing the addition order of fiber. Semicircle bending tests and indirect tensile tests were conducted to characterize the cracking behavior of CRAM at low temperature. Moreover, freeze-thaw cycle tests under both dry and water-saturated conditions were also designed to investigate the effect of fiber mixing process on the freeze-thaw damage behavior of CRAM. Finally, SEM was also used to analyze the effect of fiber mixing process on its micro dispersion in CRAM.