# Monitoring of Reinforced Concrete Corrosion: Active and Passive Bars Exposed to Climate
## 1 Introduction  
One of the most significant challenges in reinforced concrete structures is durability. And the main cause is the reinforcement corrosion that plays a prominent role in limiting the durability [1; 2; 3], prompting the need for costly maintenance and repair [4; 5; 6]. The consequences of corrosion such as cracking or even spalling of the concrete cover, a loss of bonding, and a loss of cross-section, which can lead to brittle failure of the structures, are well known [7; 8; 9; 10; 11]. For structures with active reinforcement, it is crucial to monitor the onset of corrosion to prevent stress corrosion cracking and hydrogen embrittlement. These phenomena can cause brittle fracture of the structural components [7; 12; 13; 14; 15; 16; 17; 18]. Due to complying with current regulations, reinforced concrete structures often fail to reach their intended service life due to various factors [19; 20; 21; 22]. However, there is currently no tool available to accurately evaluate these structures, which makes proper maintenance difficult. Although regulations require predictive maintenance, the lack of proper assessment tools makes it challenging to implement in practice. Predictive maintenance can only be achieved through a continuous monitoring system and accurate measurement of durability parameters [23; 24; 25]. In the case of structures exposed to the environment, corrosion can occur due to carbonation, chloride exposure, or the presence of chloride additives in concrete. This corrosion can cause damage to the concrete, including cracking and spalling of the cover due to volume expansion, a reduction in the reinforcement cross-section due to the formation of rust products, and a loss of mechanical performance in the steel. Chloride-induced corrosion can be particularly hazardous in prestressed members due to the potential for pitting, which can lead to damage localization and localized failures. As the environmental attack becomes more aggressive over time, either due to chloride content or carbonation,the capacity of corroded reinforced concrete (RC) or prestressed concrete (PC) members gradually decreases. This can result in unexpected failures due to insufficient bending, shear, or anchorage resistance [9; 11; 21]. In order to ensure the durability of structures, it is essential to calibrate and update durability models in real-time with accurate and correctly measured information on the condition of the structure. Therefore, it is necessary to increase maintenance efforts and carry out predictive assessments to anticipate or detect corrosion of both active and passive reinforcement. The strategy for managing the structure's life and planning maintenance involves integrating traditional inspection methods with new intelligent management tools. Additionally, real-time monitoring results should be incorporated and analysed to enable a shift from reactive repair to proactive diagnosis. This transition will influence the cost and scope of any necessary repairs [19; 26; 27; 28]. In order to incorporate artificial intelligence tools in infrastructure maintenance, it is necessary to have precise measurement databases. These measurements can then be integrated into finite element models or digital twins to evaluate the structure's real-time state (see Figure 1). This evaluation can be carried out either on new structures, existing structures, or repaired structures, which in turn would allow the durability and effectiveness of the repair itself to be assessed. Given the nature of corrosion itself, electrochemical techniques are the most suitable for measuring it. There are several studies and recommendations that define the methodology to be followed for a correct measurement [26; 27; 28; 29]. The corrosion potential (\(E_{corr}\)) measurement helps to identify the areas with corrosion probability. This is a qualitative parameter. Similarly, the electrical resistivity (\(\rho\)) enables the classification of areas according to moisture content, concrete porosity, and concrete microstructure [30; 31].