## 1 Introduction  
With the fast growth of civil engineering infrastructure, concrete has become a popular building material for foundations. Many researchers have studied concrete's mechanical properties and durability [1, 2, 3, 4]. Concrete consists of fine aggregate, coarse aggregate, cement, water, mineral admixtures, and chemical additives. Fine and coarse aggregates are the main parts of concrete, making up 70%-80% of the volume of concrete [5]. Most sand comes from natural rivers. The use of river sand has caused severe environmental problems. Moreover, improving the performance of concrete is essential [6, 7, 8]; therefore, looking for alternatives for fine aggregate is an urgent need. Northwest China has 80% of China's desert resources [9, 10, 11], with Xinjiang, Inner Mongolia, Gansu, and Ningxia being the most important regions. Using desert sand instead of natural river sand can help the environment in some ways and solve the lack of building materials. Researchers have made much progress in their study of how desert sand can be used [12, 13, 14, 15, 16, 17]. In engineering, the ability of concrete to bond between surfaces is essential [18, 19]. Concrete has been used in many practical projects because it is cheap and easy to make [20]. However, concrete has low tensile strength, is heavy, cracks easily, and has poor durability properties [21, 22]. Hence, these characteristics make some engineered concrete structures vulnerable to damage [23, 24]. In the past 20 years, researchers have studied engineeredcementitious composite (ECC) with ultra\(-\)high toughness [25; 26; 27; 28; 29; 30; 31] to find ways to make concrete stronger, more flexible, and less likely to crack. Steel fiber, polybutyrate alcohol (PVA) fiber, polybutylene (PE) fiber, and hybrid fibers are standard ECC fibers. PE\(-\)ECC and PVA\(-\)ECC can withstand more than 3% tensile strain without breaking. PVA fiber is inexpensive; therefore, more research has been done on PVA\(-\)ECC [32; 33]. However, at the same volume dosage, the strain capacity of PE\(-\)ECC is slightly larger than that of PVA\(-\)ECC, and the friction coefficient of PE fiber is higher than that of PVA fiber. Additionally, PE fiber repels water; thus, it will not change how ECC cement hydrates and will strengthen the bond between cement and fiber. When fibers are added to cement\(-\)based materials, they can make up for the fact that cement\(-\)based fabrics are fragile and do not have much tensile strength. The main reason to improve the bond between the cement matrix and the fiber is to make cement\(-\)based materials stronger [34]. Researchers have learned much about how ECC bonds at the interface [35; 36; 37; 38]. Previous results show that ECC can improve how well concrete bonds at the joints and can be used as a long\(-\)lasting repair material for structures. However, how ECC fiber and matrix bond at the interface when desert sand is used instead of natural sand needs more research. If desert sand is used to replace part of natural sand to prepare ECC and can meet the engineering requirements, the use of natural resources can be reduced to a great extent, and the application of ECC can be more extensive. Experiments were conducted by researchers to assess the bridging effect and toughness of ECC fiber. For example, [PERSON] et al. [39] used scanning electron microscopy (SEM) to examine the interface bonding mechanism of fiber\(-\)reinforced cementitious composite on a small scale and showed that the composite's bonding strength was higher than the tensile strength of the cement matrix. [PERSON] et al. [40] found that when the volume fraction of polypropylene fiber is 2%, the fiber plays the most obvious bridging role, and the toughness index of the concrete is the best, which leads to progressive ductile failure. Many researchers also used the combination of numerical simulation and experiments to evaluate the interface bonding properties of ECC. [PERSON] et al.