# Chloride Resistance of Assembled Bridge Piers Reinforced with Epoxy-Coated Steel Bars
## 1 Introduction  
Steel bar corrosion is the primary cause of deterioration in concrete structures [1], leading to significant losses worldwide each year [2, 3]. In the United States alone, the direct corrosion costs for highway bridges amounted to approximately USD 8.3 billion in 2014, and the American Society of Civil Engineers (ASCE) predicted that infrastructure maintenance will necessitate an investment of around USD 2 trillion by 2025 [4]. Consequently, enhancing the corrosion resistance of steel bars in concrete remains a critical focus in durability research. Epoxy-coated steel bars are currently one of the most commonly used corrosion-resistant steel bars in major coastal engineering projects. Since its introduction in the 1970s [4, 5, 6], epoxy-coated steel bars have been widely regarded as having excellent corrosion resistance [5, 7, 8, 9]. Therefore, early research mainly focused on mechanical properties, such as bond strength between epoxy-coated steel bars and concrete [4, 10, 11], with less emphasis on corrosion behavior. However, some reports and related studies suggest that the corrosion resistance of epoxy-coated steel bars may not be as excellent as previously thought. Since the 1990s, there have been some reports on the corrosion of epoxy-coated steel bars in some newly constructed projects [4, 12]. Investigations suggested that the main cause of premature corrosion can be attributed to the damage of the epoxy coating on the surface of steel bars during transportation, processing, and installation, which reduces the protective effect on the internal steel bars [2, 13]. According to the literature statistics by [PERSON] et al. [4], the research focus on epoxy-coated steel bars has gradually shifted from mechanical properties to corrosion behavior since the 2000s. [PERSON] et al. [8] found thatcorrosion of epoxy-coated steel bars often occurs at the damaged areas of the coating. [PERSON] et al. [2] employed a 1 mm diameter drill to create pre-existing damage to the epoxy coatings and found that corrosion was prone to occur in damaged areas of epoxy-coated steel bars in concrete simulating solutions with pH values below 9.2 and different pH values containing 0.6 mol/L NaCl. [PERSON] et al. [14] conducted electrochemical corrosion analysis on epoxy-coated steel bars with undamaged coatings and pre-existing coating damages. The results showed that epoxy-coated steel bars with untreated surfaces exhibited a steep polarization curve slope with no corrosion characteristics. In contrast, steel bars with damaged coatings exhibited significant corrosion polarization curve characteristics, indicating a significant decrease in corrosion resistance. Additionally, the larger the area of coating damage, the faster the corrosion rate. [PERSON] et al. [9] studied the effect of pre-exposure loading on the corrosion behavior of epoxy-coated steel bars under wet-dry cyclic conditions. They suggested that loading caused cracks in the concrete protective layer and micro-cracks in the coating and generated tensile stress in the steel bars, leading to separation between the coating and the steel substrate, thereby accelerating the corrosion of epoxy-coated steel bars. Compared with the traditional cast-in-place concrete structure, the assembled concrete structure has the advantages of labor savings, fast construction speed, and less pollution to the environment, and it has been promoted for use [15]. However, the presence of a loose and porous transition layer at the interface of the assembled joint is prone to form a chloride ion transport pathway, leading to premature corrosion of the steel bar and deterioration of the structural durability [16; 17]. [PERSON] et al. [18] studied the new and old concrete bond area by dividing it into three parts: new concrete, old concrete, and interface zone. [PERSON] et al. [19] concluded that uncoordinated shrinkage of old and new concrete is an important reason for the existence of defects at the old and new concrete interface.