## 1 Introduction  
Filler is a necessary component to maximize the stability of asphalt mixture. It plays a role in increasing the bonding between asphalt and aggregate, which is typically chosen on the basis of the material's properties [1]. Many types of waste materials can be used in various purposes, such as the replacement of mineral fillers or additives to increase the asphalt mixture performance [2]. The use of these materials can help not only to solve environmental problems, but also it can enhance the economic value to those materials [3]. The use of natural fibers in asphalt mixtures to improve the moisture damage resistance and rutting resistance has been proposed in many researches, such as fibers from banana trees [4], bamboo plants [5], cellulose [6], coconut [7,8], hemp [9], jute [10], kapok [11], peat [12,13], and sisal [14]. The capability of water absorption of each type of fiber is different. Recently, some researchers have conducted the replacement of mineral filler by bagasse ash fillers. They found that replacing bagasse ash filler in asphalt mixture can improve performances of the Marshall stability, flow, and resilient modulus of hot-mix asphalt (HMA) [15,16]. [PERSON], P.K. studied the effects of adding peat powder and peat fibers into bituminous binders and asphalt mix. It was found that adding more peat powder resulted in higher stiffness [17]. In addition, a study of coconut coir dust [18] found that the content of coconut coir dust should be optimum to obtain the mechanical properties. If the content is exceeded, the properties will change, resulting in weakening asphalt mixtures. In this study, researchers focused on the effect of using different natural fillers in asphalt mixture on moisture damage resistance. The coconut peat and bagasse were selected as fillers in this study since the quantity of these two natural waste materials in Thailand is relatively high. About 4,500,000 tons and 50,000 tons of the bagasse and coconut peat are produced a year, respectively, while about 2,000,000 tons/year of the aggregate fillers for asphalt road construction are used. As a result, the amount of natural waste materials was considered to minimize agricultural waste disposal through the substitution of aggregate fillers with bagasse and coconut peat. Nowadays, moisture damage is of concern for pavement in Thailand. It is commonly found that most pavements are damaged by moisture from rainwater and undrained water. Moisture damage can be caused by either of two main mechanisms: An adhesive failure between the asphalt binder and the aggregate surface, or a cohesive failure of the asphaltastic bond resulting from an interaction with moisture. Adhesive failure is the loss of the bond between the asphalt binder and aggregate, in which the asphalt binder acts as an adhesive and the aggregate acts as an adherend [19]. However, this failure is considered the only asphalt binder phase in asphalt mixture, which cannot address the other mechanism. Cohesion loss of asphaltastic bond is another mechanism affecting moisture damage in asphalt mixtures. It occurs when the asphalt mastic is weakened by the diffusion of water into the asphalt binder and the migration of water through the mastic to the mastic-aggregate interface [20]. By reducing the strength of the mastic due to moisture accumulation and void swelling, water may affect the coherent loss the mastic-aggregate interface [21]. To determine the adhesive and cohesive failures of asphalt binder and mastic, the Binder Bond Strength (BBS) test can be used as a robust test [22,23]. However, the most widely used moisture damage resistance standard test for asphalt mixture specimen is the indirect tensile strength (ITS) test specified in American Association of State Highway and Transportation Officials T 283 (AASHTO T 283) and Hamburg Wheel Tracking Test (HWT). There have been no robust other alternative tests that can determine the moisture damage resistance of asphalt mixture.