# Friction Behavior of Ceramic Materials for the Development of Bridge-Bearing Friction Materials
## 1 Introduction  
Bridge bearings play a critical role as ancillary components that significantly contribute to bridge durability. This is achieved by distributing superstructure loads to the substructure through frictional behavior, while accommodating thermal expansion, contraction displacements, and deflections. To ensure efficient load accommodation, transmission, and movement, the performance of the bridge bearings is crucial. However, the friction material, which is a key component of a bearing, is a decisive factor [1]. The materials used in bridge bearings must support the vertical loads of the superstructure, accommodate displacements due to horizontal movements, and transfer them to the substructure. These materials are positioned between the bridge deck and bearing element (Figure 1). Traditional friction materials used in bridge bearings, such as polytetrafluoroethylene (PTFE), ultrahigh-molecular-weight polyethylene (UHMWPE), and engineering plastics (EP), are fluoropolymer-based materials known for their excellent compressive-stress performance and superior coefficient of friction (COF) when combined with lubricants [2, 3, 4, 5]. However, owing to recurring frictional behavior during service, issues such as oxidationand loss of lubricants, wear, and deformation of materials (Figure 2) can occur, leading to performance degradation and necessitating the periodic maintenance of bridge bearings. In this context, partial repair or replacement of the material within the bridge bearing is not feasible, resulting in the replacement of the entire bearing unit, even though its average service life is 20-25 years. In addition, reinstalling bearings after material failure leads to shorter damage cycles, causing excessive financial losses. Currently, most friction materials used in bearing supports are EP, ultrahigh-molecular-weight polyethylene (UHMWPE), and polytetrafluoroethylene (PTFE) [3; 6; 7; 8]. These materials consist of inorganic compounds, with fluoropolymers as their main components [9]. Ref. [10] applied PTFE to standard bearing supports in a 40 m simple span and a two-span continuous bridge. However, PTFE is prone to tearing or deformation over prolonged use, leading to the widespread adoption of UHMWPE and EP, owing to their superior properties and higher durability. Long-term friction tests revealed that the sliding distance  
Figure 1: Configuration of bearing support (schematic diagram). Figure 2: Cause of bridge bearing replacement. (**a**) Corrosion of bridge bearing. (**b**) Wear of friction material. (**c**) Rust of high-strength brass friction material. (**d**) Corrosion of bearing supports due to rust. of EP was two to five times longer than that of PTFE [11] and its COF was three times higher than that of PTFE. Lubricants have been used to ensure smooth structural behavior [12; 13; 14; 15; 16]. However, the friction performance of these materials diminishes over time owing to lubricant depletion or deformation of the material during its extended service life. Ref. [17] developed a friction material by substituting magnesium oxide with polyvinylidene fluoride (PVDF) and demonstrated through performance analysis that it exhibited improved wear resistance and a COF similar to that of conventional PTFE. Ref. [18] analyzed the COF and long-term friction behavior of bridge bearings using EP, which can enhance the durability of PTFE, whereas [19] conducted tests and analyses of the friction characteristics of modified PTFE. However, the commonly used friction materials in bridge bearings are insufficient to accommodate the wear and damage caused by cumulative travel distances and the dynamic behavior of friction materials resulting from increased vehicle speeds and traffic volumes [9; 11]. Consequently, the demand for new materials with high compressive strength, durability, and safety is growing [9; 20; 21; 22; 23; 24]. Ceramic materials have the potential to address and overcome the issues associated with these materials.