Chapter 1: Understanding the Chemistry and Common Issues of Infrastructure Corrosion Free

Corrosion is a pervasive and complex issue with profound implications for infrastructure globally, affecting everything from bridges and pipelines to buildings and transportation systems. This electrochemical process occurs when metals interact with environmental factors such as moisture, oxygen, and salts, leading to their gradual degradation. For instance, the infamous corrosion of the Tacoma Narrows Bridge in Washington State, known as “Galloping Gertie,” illustrates how structural failure can result from an inadequate understanding of corrosion and fatigue.^1–3  The bridge, which collapsed in 1940 due to aerodynamic forces compounded by metal fatigue, highlighted the critical need for considering environmental interactions in infrastructure design. Similarly, the corrosion of underwater pipelines presents a significant challenge worldwide. The corrosion of oil and gas pipelines, such as those in the North Sea and the Gulf of Mexico, leads to substantial financial losses and environmental hazards. In the North Sea, frequent pipeline failures due to corrosion not only incur high repair costs but also pose environmental risks, such as oil spills that harm marine ecosystems.^4,5  The industry has since invested heavily in corrosion-resistant materials and advanced monitoring technologies to mitigate these issues. In the realm of urban infrastructure, the corrosion of reinforced concrete structures is a common problem. For example, in Mumbai, India, the city’s coastal location and high humidity accelerate the corrosion of reinforcing steel in concrete buildings, leading to widespread structural damage and safety concerns. This issue has necessitated the development of more durable concrete mixtures and protective coatings to extend the lifespan of infrastructure. Globally, the corrosion of infrastructure also impacts transportation systems. In the United States, the corrosion of steel bridges has led to increased maintenance costs and safety concerns. The federal government has invested in regular inspections and corrosion prevention strategies to manage the risk associated with aging infrastructure. Similarly, in Japan, the corrosion of railway tracks and supporting structures necessitates continuous monitoring and maintenance to ensure the safety and reliability of the extensive rail network.^6,7  The study of corrosion is not merely an academic exercise but a critical necessity for developing effective strategies to manage and mitigate its impacts. Understanding corrosion involves delving into the underlying electrochemical mechanisms, including the roles of anodes, cathodes, electrolytes, and the reactions occurring at these sites. This knowledge enables scientists and engineers to identify material vulnerabilities and devise targeted interventions to prevent or slow down corrosion. Beyond the scientific understanding, the economic ramifications of corrosion are substantial. Corrosion-related damage incurs significant costs related to repair, replacement, and operational downtime, which can be particularly burdensome for industries reliant on critical infrastructure, such as transportation, construction, and energy. Effective management and preventive strategies can help mitigate these costs, highlighting the importance of investing in corrosion research and technology. Figure 1.1 shows the fissuring and chipping owing to element breakdown in an offshore structure.

The safety implications of corrosion are equally critical. Infrastructure failures due to corrosion can have catastrophic consequences, posing severe risks to human safety and property. Examples include the collapse of bridges, the rupture of pipelines, or the deterioration of building supports—all of which can lead to accidents with devastating outcomes. Ensuring that infrastructure is protected against corrosion is essential for maintaining public safety and preventing such incidents. Moreover, corrosion can complicate maintenance and repair efforts.⁹  Corroded components may require specialized techniques for removal and replacement, and the full extent of the damage may not be apparent until it has reached a critical stage. This makes regular inspections and proactive maintenance vital to identifying and addressing corrosion issues before they escalate into more severe problems. Corrosion profoundly affects both the aesthetic and functional aspects of infrastructure, impacting how structures are perceived and used, even when immediate safety is not compromised. For example, visible corrosion on iconic landmarks such as the Eiffel Tower in Paris or the Sydney Harbour Bridge in Australia can significantly detract from their visual appeal.^10,11  These structures, despite their ongoing maintenance, display rust and degradation over time, which not only impacts their appearance but can also diminish their status as symbols of cultural heritage and engineering prowess. The aesthetic degradation of such landmarks can influence public perception, affecting tourism and local pride. Functional aspects are similarly compromised by corrosion. In buildings, corroded steel reinforcements can lead to cracks and structural weaknesses, reducing the overall functionality and usability of the space. For instance, in urban areas like New York City, older infrastructure such as subway systems and bridges often faces challenges due to corrosion, affecting their operational efficiency and requiring frequent repairs. Corrosion-induced damage can result in service interruptions, impacting daily commutes and economic activities.^12,13 

Beyond these visual and functional issues, corrosion has notable environmental repercussions. Degraded infrastructure, such as corroded pipelines or storage tanks, can lead to the release of harmful substances into the environment. For example, corroded pipelines in the oil and gas industry can leak hazardous chemicals into the soil and groundwater, causing long-term environmental damage and health risks. In coastal areas, corroded marine infrastructure, such as piers and docks, can release pollutants into the sea, affecting marine ecosystems and biodiversity. The disposal of corroded materials also contributes to environmental pollution. Materials such as corroded steel and concrete, when not properly managed, can end up in landfills, releasing pollutants and contributing to waste accumulation.^14,15  To mitigate these issues, there is a growing emphasis on developing sustainable materials and coatings that not only enhance the durability of infrastructure but also minimize environmental impact. Innovations in corrosion-resistant coatings, such as those using environmentally friendly materials, aim to reduce the release of harmful substances and extend the lifespan of infrastructure. Additionally, research into recyclable materials and eco-friendly disposal methods helps address the environmental concerns associated with corroded infrastructure.

Uniform corrosion, also known as general corrosion, is the most common and easily recognizable form of corrosion. It occurs evenly across the surface of a material, leading to a consistent loss of material thickness over time.²⁷  This type of corrosion is characterized by a uniform and predictable rate of degradation, often facilitated by exposure to corrosive environments such as moisture, acids, or salts. The fundamental mechanism behind uniform corrosion involves electrochemical reactions that occur uniformly across the material surface. For instance, in the case of iron exposed to moisture and oxygen, uniform corrosion results in the formation of iron oxide (rust), which gradually reduces the thickness of the metal. The process involves the oxidation of iron and the reduction of oxygen and water, leading to rust formation. Uniform corrosion typically progresses at a rate that can be predicted and measured, making it relatively easier to manage compared to other forms of corrosion. Preventive measures include applying protective coatings, using corrosion-resistant materials, and employing corrosion inhibitors. Despite its predictability, uniform corrosion can still have significant impacts on infrastructure, especially when the material loss becomes substantial and affects the structural integrity of components. One of the most notable examples of uniform corrosion is the rusting of iron and steel structures. For instance, steel bridges and pipelines exposed to rain and atmospheric oxygen are prone to uniform corrosion. Regular maintenance and inspection are essential to mitigate the effects of uniform corrosion, ensuring that protective measures are in place to maintain structural integrity and extend the lifespan of these critical infrastructure elements.

Pitting corrosion is a localized form of corrosion that leads to the formation of small, deep pits or cavities on the surface of a material. Unlike uniform corrosion, which affects the entire surface, pitting corrosion is characterized by its localized nature and can cause severe damage even when the overall material loss is minimal. This type of corrosion is particularly insidious because it can lead to significant structural failures without substantial overall weight loss. The mechanism of pitting corrosion involves the breakdown of the protective oxide layer on the material surface, which can be initiated by factors such as chloride ions, acidic environments, or localized changes in pH. Once the protective layer is compromised, the underlying metal becomes susceptible to aggressive attack, leading to the formation of pits.^28,29  The pits act as small electrochemical cells, where the metal at the bottom of the pit undergoes oxidation, while the surrounding areas act as cathodes. Pitting corrosion is a significant concern in environments where chloride ions are present, such as in seawater or de-icing salts. For example, stainless steel used in marine environments is prone to pitting corrosion due to the high chloride concentration in seawater. The pits can penetrate deeply into the material, leading to potential perforation and structural failure. Effective prevention of pitting corrosion involves the use of corrosion-resistant alloys, protective coatings, and proper design considerations to minimize exposure to corrosive environments. Regular inspection and monitoring are also crucial to detect and address pitting corrosion before it leads to significant damage.

Crevice corrosion occurs in confined spaces or crevices where the environment is stagnant and isolated from the surrounding area. This type of corrosion is characterized by the formation of localized corrosion within crevices or gaps in materials, such as those found under gaskets, washers, or in the joints of structures. Crevice corrosion can be particularly challenging to manage because it often goes unnoticed until significant damage has occurred. The mechanism of crevice corrosion involves the differential aeration between the crevice and the surrounding area. Inside the crevice, the concentration of corrosive agents such as chloride ions can become significantly higher than in the surrounding environment, creating a localized electrochemical cell. The reduced oxygen availability within the crevice leads to a low pH environment, further accelerating the corrosion process.^30,31  Crevice corrosion is commonly encountered in environments where equipment or structures have gaps or joints, such as flanges, bolts, and under insulation. For example, in the chemical processing industry, equipment with tight seals and gaskets can be susceptible to crevice corrosion due to the accumulation of corrosive chemicals within the crevices. Preventive measures for crevice corrosion include designing equipment with smooth, accessible surfaces that minimize the potential for trapped corrosive agents. Regular inspection and maintenance are also essential to identify and address crevice corrosion early. Additionally, using corrosion-resistant materials and applying protective coatings can help mitigate the risk of crevice corrosion.

Galvanic corrosion, also known as dissimilar metal corrosion, occurs when two different metals come into electrical contact in the presence of an electrolyte. This type of corrosion results from the electrochemical reaction between the two metals, where one metal (the anode) corrodes preferentially, while the other metal (the cathode) is protected. The rate of galvanic corrosion depends on the relative positions of the metals in the galvanic series and the characteristics of the electrolyte. The galvanic corrosion mechanism involves the establishment of a galvanic cell, where the more anodic metal corrodes and releases electrons, while the more cathodic metal undergoes a reduction reaction. For example, when aluminum (more anodic) and stainless steel (more cathodic) are in contact in the presence of an electrolyte, aluminum corrodes preferentially.^32,33 

Galvanic corrosion can occur in various applications, such as in plumbing systems, where dissimilar metals are joined. For instance, in a water distribution system, copper and steel pipes may be connected, leading to galvanic corrosion of the steel pipes. Similarly, in marine environments, the use of different metals in ship hulls can result in galvanic corrosion, leading to accelerated deterioration of the less noble metal. Preventing galvanic corrosion involves isolating dissimilar metals from each other using non-conductive materials or coatings. Additionally, selecting metals with similar electrochemical properties and employing sacrificial anodes can help protect the more susceptible metals. Proper design and material selection are critical in applications where dissimilar metals are used to ensure long-term durability and performance.

Stress-corrosion cracking (SCC) is a type of corrosion that occurs in metals under the combined influence of tensile stress and a corrosive environment. This form of corrosion is characterized by the formation of cracks that propagate through the material, often leading to sudden and catastrophic failure. SCC is particularly problematic in high-stress applications where materials are subjected to both mechanical loads and corrosive conditions. The mechanism of stress-corrosion cracking involves the interaction between tensile stress and a corrosive environment, leading to the initiation and propagation of cracks. The tensile stress can be applied externally, such as in pressure vessels or pipelines, or arise from residual stresses in the material. The corrosive environment contributes to the crack initiation by weakening the metal and reducing its resistance to stress. For example, in the case of stainless steel exposed to chloride environments, the presence of tensile stress and chloride ions can lead to SCC. SCC is commonly observed in various industries, including aerospace, petrochemical, and nuclear power.^34,35  For example, in the aerospace industry, aircraft components exposed to high-stress and corrosive environments can develop SCC, leading to potential structural failures. In the petrochemical industry, pipelines and pressure vessels are susceptible to SCC due to the combination of operational stresses and corrosive chemicals. Preventing SCC involves managing both the stress and corrosive environment. This can be achieved through material selection, design modifications to reduce stress concentrations, and the use of protective coatings or corrosion inhibitors. Additionally, regular inspection and maintenance are crucial to detect and address SCC before it leads to significant failures.

Material composition is a fundamental determinant of corrosion susceptibility, influencing how different materials, especially metals, interact with their environments. Metals such as iron, steel, and aluminum exhibit distinct corrosion behaviors based on their chemical properties and the presence of alloying elements. Iron, for example, is highly prone to rusting when exposed to moisture and oxygen, resulting in the formation of iron oxide.^36,37  This is due to iron’s tendency to undergo oxidation, which leads to the gradual deterioration of its structural integrity. The rate at which rust forms can be influenced by the presence of impurities or alloying elements in the iron. High-carbon steel, used in various applications, rusts more quickly because of its higher iron content and lower inherent resistance to environmental factors. Steel, being an alloy of iron and carbon, demonstrates a more intricate corrosion profile. The addition of elements such as chromium, nickel, and molybdenum can significantly enhance its resistance to corrosion. Stainless steel, for instance, contains chromium which forms a protective oxide layer on its surface. This layer is crucial for preventing further corrosion and provides excellent resistance under many conditions. However, in environments containing chlorides, such as seawater or de-icing salts, this protective layer can be compromised, leading to localized corrosion phenomena such as pitting. The effectiveness of the protective layer can also be affected by the presence of other alloying elements and specific environmental conditions. Aluminum presents a different case with its corrosion resistance. It forms a protective oxide layer almost immediately upon exposure to air. This layer acts as a barrier, protecting the underlying metal from further corrosion and making aluminum suitable for various applications, including aerospace and architectural components. However, this protective layer is vulnerable in highly acidic or alkaline environments. In such conditions, the layer can be disrupted, leading to increased corrosion rates. The effectiveness of aluminum’s oxide layer can also be compromised by mechanical damage or abrasion, which can expose the underlying metal to further degradation.

The composition of alloys plays a crucial role in their corrosion resistance. For instance, adding copper to steel can enhance its resistance to atmospheric corrosion. This type of steel, known as weathering steel, forms a protective patina on its surface, which reduces the need for painting and maintenance.^38–40  Conversely, certain alloying elements can make materials more susceptible to specific types of corrosion. For example, sulfur in steel can promote corrosion in sulfuric acid environments, leading to accelerated material degradation. This is particularly relevant in industries where sulfuric acid is used or produced. Beyond metals, polymers, ceramics, and composites also exhibit varying degrees of corrosion resistance based on their chemical compositions. Polymers are generally more resistant to corrosion than metals due to their chemical stability and lack of electrochemical reactivity. They are used in applications where resistance to moisture, chemicals, and environmental factors is essential. However, polymers can still degrade due to factors such as UV radiation and chemical exposure, which can affect their mechanical properties and structural integrity.^41,42  Ceramics, known for their high chemical stability and resistance to oxidation, are used in environments with high temperatures and aggressive chemicals. Despite their overall resistance, ceramics can experience degradation due to mechanical stresses and thermal shock. Composites, which combine different materials to achieve specific performance characteristics, also show diverse corrosion behaviors. The resistance of composites depends on the properties of the individual components and their interactions. For instance, fiber-reinforced composites used in marine applications benefit from the corrosion resistance of both the fibers and the matrix material, although the interface between these components can be a weak point.

Environmental exposure is another critical factor influencing corrosion. The surrounding environment interacts with the material’s surface, affecting its susceptibility to corrosion. Key environmental factors include moisture, temperature, atmospheric pollutants, and the presence of electrolytes. Moisture is a primary driver of corrosion, as it facilitates the electrochemical reactions that lead to material degradation. In the presence of water, metal surfaces can become anodes, where oxidation occurs, while the surrounding area acts as a cathode.^43–45  This process is exacerbated in environments where water is contaminated with salts or acids, such as coastal or industrial areas. For example, coastal structures are often subjected to saline environments, which accelerate corrosion due to the presence of chloride ions. Temperature also plays a significant role in corrosion. Higher temperatures generally increase the rate of corrosion by accelerating chemical reactions. In many cases, elevated temperatures can enhance the solubility of corrosive agents, leading to more aggressive corrosion. Conversely, low temperatures can reduce the rate of corrosion but may also lead to issues such as ice formation, which can physically damage protective coatings and increase corrosion risk.^46,47 

Atmospheric pollutants, such as sulfur dioxide, nitrogen oxides, and ozone, can contribute to corrosion by reacting with moisture to form acidic solutions. Acid rain, resulting from the combination of these pollutants with rainwater, can significantly accelerate the corrosion of metals and other materials. For example, urban and industrial areas with high levels of air pollution often experience accelerated corrosion of building facades, bridges, and other infrastructure. The presence of electrolytes, such as salts and acids, can also influence corrosion. Electrolytes facilitate the electrochemical processes that drive corrosion, leading to increased material degradation. In industrial settings, acidic or alkaline environments can cause significant corrosion of equipment and pipelines. For instance, in chemical processing plants, exposure to acidic or alkaline solutions can lead to severe corrosion of metal components, requiring careful material selection and protective measures.

Operational conditions encompass the specific circumstances under which materials are used, including mechanical stresses, load conditions, and exposure to chemicals or other agents. These conditions have a profound impact on the rate and type of corrosion that materials experience, affecting their longevity and performance. Mechanical stresses are a significant factor influencing corrosion behavior. These stresses, which can be tensile, compressive, or bending, create localized areas of high stress that can promote corrosion processes. For instance, stress-corrosion cracking (SCC) occurs when a material is subjected to tensile stress in the presence of a corrosive environment. This form of corrosion is particularly problematic as it leads to the formation of cracks that can propagate over time, potentially leading to catastrophic structural failures.^48,49  In high-stress applications such as pressure vessels, pipelines, and aircraft components, SCC poses a serious risk. The combination of mechanical stress and a corrosive environment can accelerate the degradation of materials, making it essential to account for both factors during design and material selection. Load conditions further impact corrosion behavior. Cyclic loading, where materials undergo repeated loading and unloading, can lead to fatigue corrosion. This type of corrosion occurs when repeated mechanical stress causes the formation and growth of cracks on the material surface, which are then exacerbated by the corrosive environment. In structures like bridges and other infrastructure subjected to dynamic loads, fatigue corrosion can result in premature failure if not managed properly. For example, the repeated stress from vehicle traffic on bridges can contribute to fatigue corrosion, necessitating regular inspections and maintenance to ensure structural integrity.

Exposure to chemicals or other corrosive agents during operation is another critical factor influencing corrosion. Many industrial processes involve materials coming into contact with aggressive chemicals such as acids, alkalis, or solvents. These chemicals can significantly accelerate the rate of corrosion, leading to equipment degradation and potential failures. In the petrochemical industry, for example, pipelines and storage tanks often face harsh operating conditions due to exposure to corrosive chemicals.^50–52  To mitigate these effects, specialized materials and coatings are used to enhance resistance to chemical corrosion and prolong the lifespan of equipment. Operational conditions such as temperature fluctuations, pressure changes, and flow rates also play a role in corrosion behavior. High temperatures and pressures in chemical reactors, for instance, can lead to accelerated corrosion rates due to enhanced chemical reactions and increased solubility of corrosive agents. Conversely, temperature fluctuations can cause thermal cycling effects, which contribute to material degradation by inducing thermal stresses and causing expansion and contraction in the material. This can result in additional strain and potential cracking, further exacerbating corrosion problems. Proper design and material selection are crucial to address these operational conditions and mitigate their impact on corrosion.

Steel structures are widely used in infrastructure due to their strength, versatility, and cost-effectiveness. However, steel is highly susceptible to corrosion, which can compromise its structural integrity and lead to costly repairs and replacements. The primary corrosion issues in steel structures include uniform corrosion, pitting corrosion, and rust formation. Uniform corrosion in steel structures typically results from exposure to moisture and oxygen. When steel is exposed to these elements, it undergoes an electrochemical reaction that leads to the formation of iron oxide or rust. This corrosion process results in a gradual loss of material thickness, reducing the steel’s load-bearing capacity and overall performance.^53,54  Pitting corrosion is another significant issue for steel structures, particularly in environments where chloride ions are present, such as coastal areas or de-icing applications. Pitting corrosion is localized and results in the formation of small, deep pits on the steel surface. These pits can penetrate through the material, leading to structural weakness and potential failure. Rust formation, which is a visible sign of corrosion, not only affects the aesthetic appearance of steel structures but also accelerates further degradation. Rusting occurs when iron reacts with oxygen and moisture, forming a flaky, reddish-brown substance. This substance can expand and cause the underlying steel to deteriorate.

To mitigate corrosion in steel structures, several strategies can be employed. One effective approach is the application of protective coatings. Coatings such as paints, primers, and galvanizing provide a barrier between the steel surface and corrosive agents, preventing direct contact and slowing down the corrosion process. For example, hot-dip galvanizing involves coating steel with a layer of zinc, which acts as a sacrificial anode and protects the underlying steel from corrosion. Another strategy is the use of corrosion-resistant alloys. Alloying elements such as chromium, nickel, and molybdenum can enhance the steel’s resistance to corrosion. Stainless steel, which contains chromium, is particularly effective in resisting corrosion, making it suitable for applications in harsh environments.⁵⁵  Regular maintenance and inspection are also critical for managing corrosion in steel structures. Routine inspections can help identify early signs of corrosion, such as rust or pitting, allowing for timely repairs and preventive measures. Additionally, implementing a comprehensive maintenance plan that includes cleaning, coating application, and monitoring can extend the lifespan of steel structures. In several experiments, for instance, Liu et al.⁶  examined the impact of ambipolar stray current (SC) interference on the corrosion behavior of steel fibers in steel fiber-reinforced concrete (SFRC). Stray currents are a common issue in marine civil engineering structures, where unintended electrical currents can circulate through the steel reinforcements, causing accelerated corrosion. The research was conducted by a team from two key institutions in Shenzhen, China: the Guangdong Provincial Key Laboratory of Durability for Marine Civil Engineering and the Institute of Technology for Marine Civil Engineering. Their investigation focuses on both simulated pore solutions and actual concrete environments, offering insights into how steel fibers degrade under the influence of stray currents and chloride ions. Through a combination of corrosion morphology analysis, weight loss experiments, and electrochemical testing, the researchers explored how ambipolar stray currents affect the passivation and corrosion processes of steel fibers. In the simulated pore solution environment, the study revealed that short-term exposure to stray currents had a relatively limited effect on the steel fibers.^56,57  However, when chloride ions (Cl⁻) were introduced into the environment, the protective passive film on the steel fibers was compromised. Chloride ions weaken or even destroy the self-healing ability of the passive film, leading to the initiation and acceleration of pitting corrosion on the surface of the steel fibers. For the SFRC samples, the stray current created an electrical circuit through the dispersed steel fibers, and the resistance within the system was found to depend on the content and distribution of the steel fibers. While concrete itself provided some level of protection against corrosion, this was insufficient when intense stray currents were combined with the presence of chloride ions. Under these conditions, severe corrosion occurred in the SFRC, with the most pronounced damage concentrated at the ends of the steel fibers. This suggests that, despite the durability of SFRC, exposure to strong electrical interference and aggressive chloride environments significantly compromises the integrity of steel fibers, highlighting the need for improved corrosion protection strategies in marine civil engineering applications. Similarly, Subbiah et al.¹⁹  focused on addressing a critical issue in the field of civil engineering: the corrosion of steel rebar in chloride-contaminated environments, which is a leading cause of infrastructure deterioration globally. Steel reinforcement in concrete structures is particularly vulnerable to chloride ions, which can penetrate concrete and compromise the protective passive film on steel, leading to accelerated corrosion. Corrosion not only weakens the structural integrity of concrete but also increases maintenance and repair costs. Thus, developing effective corrosion inhibitors is crucial for prolonging the lifespan of steel-reinforced concrete structures, especially in harsh environments such as marine or industrial settings. This study introduces a novel hydrazone derivative, (E)-N′-(4-(dimethylamino)benzylidene)-2-(5-methoxy-2-methyl-1H-indol-3-yl)aceto-hydrazide (HIND), and investigates its potential to protect steel rebar from corrosion in chloride-laden concrete pore solutions (ClSCPS). To assess the effectiveness of HIND as a corrosion inhibitor, the researchers employed a combination of experimental and theoretical approaches. Initially, corrosion was evaluated using weight loss experiments and electrochemical methods, including potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). These techniques allowed for the quantification of the inhibition efficiency of HIND and its impact on the corrosion rate of steel rebar over a 30-day immersion period. The experimental results demonstrated that HIND significantly reduced corrosion, achieving an inhibition efficiency of 88.4% at an optimal concentration of 0.5 mmol L⁻¹. This indicates that even at relatively low concentrations, HIND is highly effective in protecting steel from aggressive chloride environments. A key aspect of the study was the detailed surface analysis of steel rebar using advanced characterization techniques. Field emission scanning electron microscopy (FE-SEM) combined with energy-dispersive spectroscopy (EDS) provided insights into the surface morphology of the steel before and after exposure to the corrosive environment. The results revealed that the steel surface in the presence of HIND showed significantly less degradation compared to the uninhibited samples. Atomic force microscopy (AFM) measurements confirmed a drastic reduction in surface roughness from 183.5 nm in uninhibited solutions to just 50 nm in the inhibited samples, further highlighting the protective effect of HIND.

In addition to surface morphology, X-ray photoelectron spectroscopy (XPS) was employed to investigate the chemical states of the steel surface. XPS analysis provided direct evidence of the adsorption of HIND molecules onto the steel rebar, confirming that the inhibitor forms a protective layer on the surface. This adsorption is crucial for preventing chloride ions from penetrating and initiating corrosion processes. Moreover, X-ray diffraction (XRD) analysis of the steel surface confirmed that the crystal structure remained largely intact in the presence of HIND, further emphasizing the inhibitor’s ability to stabilize the steel and prevent corrosion-induced damage. To complement the experimental findings, the study incorporated theoretical modeling using self-consistent-charge density-functional tight-binding (SCC-DFTB) simulations. These simulations provided a molecular-level understanding of the interaction between HIND molecules and the steel surface. The SCC-DFTB results revealed that the inhibition mechanism is primarily driven by the formation of chemical bonds between the active sites of the HIND molecules and the iron atoms on the steel surface. Specifically, the simulations showed that charge transfer from the inhibitor to the iron atoms played a key role in the formation of a stable protective layer, which blocked further corrosion. The combination of experimental results and theoretical modeling provided a comprehensive understanding of how HIND works as an anti-corrosion agent. The study demonstrated that HIND forms a durable protective film on the steel surface, effectively preventing the ingress of chloride ions and mitigating corrosion. The findings suggest that HIND could be a viable solution for extending the service life of reinforced concrete structures in environments where chloride-induced corrosion is a major concern.

Kim et al.³⁷  focused on monitoring the corrosion behavior of steel reinforcements embedded in cement mortar subjected to alternating wet-and-dry cycles, simulating conditions typically found in marine environments with high chloride concentrations. The primary goal was to assess the corrosion rate of steel rebar under these cyclic conditions using electrochemical impedance spectroscopy (EIS), a technique known for its effectiveness in monitoring corrosion processes in reinforced concrete. The experimental setup involved the preparation of seven cement mortar specimens, each designed to evaluate the impact of varying cover thicknesses (ranging from 5 to 50 mm) and rebar distances (from 10 to 80 mm) on the electrical resistance of the concrete and the corrosion rate of the steel reinforcement (Figure 1.3). These variables are critical in understanding how the structural configuration of reinforced concrete can influence its vulnerability to corrosion, particularly in chloride-rich environments. The research aimed to simulate realistic marine conditions by subjecting the cement mortar specimens to 25 cycles of alternating wet and dry conditions. Each cycle consisted of 8 hours of immersion in a 3 wt% sodium chloride (NaCl) solution, followed by 16 hours of drying at room temperature.

Electrochemical impedance spectroscopy was employed to monitor the corrosion behavior throughout these cycles. Measurements were performed using an AC impedance method across the frequency range from 100 kHz to 1 mHz. The selection of specific frequencies corresponding to the solution resistance and charge transfer resistance allowed for rapid and precise measurements of the corrosion rate. The EIS data provided insights into the electrochemical processes occurring at the steel–concrete interface, including the formation and evolution of corrosion products such as rust. The results revealed several key findings. One of the most notable observations was the significant reduction in the maximum phase shift, which decreased to approximately −30°, indicating the development of rust layers on the surface of the steel rebar (Figure 1.4). This rust formation played a crucial role in accelerating the corrosion process, especially during the drying phase of the wet–dry cycles. The drying stage was identified as the period when the corrosion rate increased most rapidly, likely due to the concentration of chloride ions and the loss of moisture, which facilitated the electrochemical reactions responsible for corrosion. Additionally, the study highlighted the influence of cover thickness and rebar distance on the corrosion rate. Thinner concrete covers and shorter rebar distances were found to be more susceptible to corrosion, as they provided less protection against chloride ingress and allowed for greater exposure of the steel to the corrosive environment. Conversely, thicker covers and larger distances between rebars contributed to a higher electrical resistance, which helped reduce the corrosion rate by limiting the access of chloride ions and moisture to the steel surface.

Yang et al.⁵⁸  explored the development of advanced epoxy nanocomposite coatings for the corrosion protection of mild steel. It addresses the challenge of selecting appropriate coatings that can effectively protect metallic surfaces, particularly when fillers or dispersing agents are incorporated into polymer matrices. The research introduces a novel approach using molecularly engineered nanofillers, specifically silica nanoparticles functionalized with a siloxane-based corrosion inhibitor precursor (NPInh). The chemical grafting of the corrosion inhibitor precursor onto the surface of silica nanoparticles enhances their performance in preventing corrosion. The focus then shifted to examining the properties of the functionalized nanofillers when blended into epoxy coatings applied to mild steel. The study found that the surface modification of silica nanoparticles with the inhibitor precursor improved the dispersion of nanofillers in the epoxy matrix. This uniform distribution of nanofillers is crucial for enhancing both the mechanical properties and the corrosion resistance of epoxy nanocomposite coatings. The nanoparticles provided mechanical reinforcement, while the corrosion inhibitor component acted as a barrier to corrosion, offering dual protection for the steel substrate. The experimental results showed significant improvements in the performance of the nanocomposite coatings. Electrochemical tests revealed a considerable reduction in corrosion current (as low as 10⁻¹⁰ A cm⁻²), indicating a marked decrease in the corrosion rate. The protection efficiency of the NPInh-modified coatings reached 99.9% after immersion in a 3.5 wt% NaCl solution, demonstrating their effectiveness in harsh environments. Additionally, the coatings exhibited enhanced strain durability, impact resistance, and adhesion strength, further contributing to their corrosion protection capabilities. Moreover, the study evaluated the durability of the coatings using salt spray tests. The NPInh-modified nanocomposite coatings displayed remarkable resistance to salt spray, maintaining integrity and protection for up to 1000 hours. This high salt spray resistance underscores the coating’s ability to perform in corrosive conditions, making it a promising candidate for long-term corrosion protection of steel structures.

Aluminum is valued for its light weight, strength, and resistance to corrosion. However, aluminum components are not immune to corrosion issues. The primary corrosion concerns for aluminum include pitting corrosion, intergranular corrosion, and exfoliation corrosion. Pitting corrosion in aluminum is similar to that in steel, characterized by localized, deep pits that can penetrate the material. This type of corrosion is often exacerbated by exposure to chloride ions, such as those found in seawater or road de-icing salts.^59,60  The presence of chloride ions can disrupt the protective oxide layer on the aluminum surface, leading to the formation of pits. Intergranular corrosion occurs along the grain boundaries of aluminum alloys, where the material is more susceptible to attack. This type of corrosion can be particularly problematic in high-strength aluminum alloys used in aerospace and structural applications. Intergranular corrosion can cause significant degradation and loss of material strength. Exfoliation corrosion is a more severe form of corrosion that occurs in aluminum alloys with a layered structure. It involves the delamination of the material in layers, leading to a significant reduction in structural integrity. Exfoliation corrosion is often observed in high-strength aluminum alloys exposed to aggressive environments.

To mitigate corrosion in aluminum components, several strategies can be employed. One effective method is the application of protective coatings. Anodizing, a process that involves forming a protective oxide layer on the aluminum surface, can enhance corrosion resistance. The anodized layer provides a durable barrier against corrosive agents and improves the material’s overall performance. Another approach is the use of corrosion-resistant alloys. Aluminum alloys with higher concentrations of elements such as manganese and silicon exhibit improved resistance to corrosion. Selecting the appropriate alloy for specific applications can help mitigate corrosion issues and extend the lifespan of aluminum components. Regular cleaning and maintenance are also essential for managing corrosion in aluminum components. Removing contaminants such as salts, dirt, and pollutants from the surface can prevent the formation of corrosive conditions. Additionally, implementing a maintenance plan that includes inspections and preventive measures can help address corrosion issues before they lead to significant damage.^61,62  For instance, Shittu et al.⁶³  introduced a comprehensive and specialized structural reliability assessment (SRA) framework to evaluate the safety and performance of horizontally curved aluminum bridge decks supported by steel I-girders. These types of bridge decks, due to their curved design, often encounter unique structural challenges, particularly under varying load conditions. The framework is designed to assess structural reliability using a combination of deterministic and probabilistic methods, adhering to the guidelines established by the American Association of State Highway and Transportation Officials (AASHTO) Load and Resistance Factor Design (LRFD) specifications. Specifically, the focus is on the proprietary Alumadeck™ system, which is a bridge deck made of aluminum alloy designed for curved configurations. The finite element analysis (FEA) simulations are a key component of the framework, allowing for a detailed examination of how the bridge structure responds to different load scenarios.^64,65  These include not only the bridge’s self-weight but also stochastic truck axle loads, which represent the random and variable nature of vehicular traffic. The simulations were performed using ABAQUS CAE software, which enabled the researchers to capture critical structural responses such as stress distribution, deflection, and strain at various points on the bridge deck. These responses were then used to derive the limit state function (LSF), a mathematical expression that defines the boundary between safe and failed states of the structure. To quantify the safety of the bridge system, the SRA framework incorporates the first-order reliability method (FORM), a probabilistic approach used to calculate the reliability index (RI), β. The reliability index represents the safety margin of the structure, with higher values indicating greater safety. The iterative FORM algorithm was employed to process the data from the FEA simulations and to calculate the RI based on different geometric properties and load combinations.^66,67  This probabilistic approach is crucial for accounting for the inherent uncertainties in material properties, load applications, and environmental factors that affect the long-term performance of bridge decks.

The study found that the Alumadeck™ system meets the AASHTO LRFD specifications, which require a target reliability index of 3.5 for a resistance factor (RF) of 1.0, assuming 80% composite action in the compression flange.^68,69  This composite action refers to the interaction between the aluminum deck and the steel girders, which work together to resist loads. The research revealed that this composite action plays a significant role in determining the overall safety of the bridge. For instance, full composite action, where the deck and girders act as a single unit, resulted in a high safety index. However, the study also identified that the minimum allowable composite action for safe performance is 40%, which corresponds to a lower safety index of 1.16. This finding highlights the importance of ensuring adequate composite action during the design and construction phases to avoid structural failure. The researchers also conducted a detailed design check to ensure that the Alumadeck™ system could withstand the stochastic axle loads specified by the HL-93 load model, which is commonly used in bridge design. The HL-93 load model includes both truck and lane loads, simulating the real-world conditions a bridge might face during its service life. The study confirmed that the Alumadeck™ system satisfies all the design criteria under these loading conditions, provided certain design parameters are maintained. One such parameter is the stiffener thickness, which, based on FEA simulations, should be a minimum of 7 mm to provide adequate structural support and prevent localized failure. The findings from this research are significant because they demonstrate that the proprietary Alumadeck™ system not only complies with the stringent AASHTO LRFD standards but also provides robust structural performance in curved bridge applications. The use of aluminum in bridge decks offers several advantages, such as reduced weight and improved resistance to corrosion, but it also introduces new challenges related to structural behavior under loads. The SRA framework developed in this study addresses these challenges by integrating advanced simulation techniques with probabilistic analysis, providing a thorough and reliable method for assessing the safety of such systems.

Similarly, Tiwari et al.⁷⁰  explored the effects of incorporating silicon carbide (SiC) nanoparticles into the joint of dissimilar aluminum alloys (2024 and 7075) during double-sided friction stir welding (DS-FSW). This technique was employed to assess how the introduction of nanoparticles influences mechanical behavior, particularly focusing on crack growth resistance and overall joint strength. The researchers carried out a microstructural analysis of the fractured surfaces to evaluate the role of nanoparticles in crack propagation, while field emission scanning electron microscopy (FESEM) was used to investigate grain size variations across different regions of the weld. Electron backscatter diffraction (EBSD) analysis of the DS-FSW joints with SiC-reinforced particles revealed distinct shear texture components such as B/B⁻ and C. Additionally, deformed textures like the rotating cube (H) {001} 〈110〉 and F {111} 〈112〉 were detected, alongside recrystallization textures, including Goss {110} 〈001〉, P {011} 〈112〉, and cube {001} 〈101〉. Mechanical properties were evaluated through hardness and tensile strength tests, comparing the SiC nanoparticle-reinforced welds to those without nanoparticle addition and the base metals. Crack growth tests were conducted using compact tension (CT) specimens under a maximum load of 5 kN and a stress ratio of R = 0.1. The inclusion of SiC nanoparticles led to a significant grain size reduction and enhanced hardness in the stir zone when compared to the base metal and samples without nanoparticle reinforcement. The study reported a notable improvement in mechanical properties, with tensile strength increasing by approximately 62% and a significant rise in microhardness in the aluminum alloy metal matrix composites (AAMMCs) developed during the welding process. By refining the microstructure and enhancing the weld’s mechanical performance, SiC nanoparticle incorporation demonstrates the potential to significantly strengthen dissimilar aluminum alloy joints formed through DS-FSW. Additionally, Oyewole et al.⁷¹  examined the thermodynamic and adsorption characteristics of a blended extract from guava and mango leaves as a corrosion inhibitor for aluminum alloy 7075 in hydrochloric acid. The research utilized weight loss measurements and polarization techniques, optimizing the process through a Box–Behnken design (BBD) that considered four key variables: acid concentration, inhibition ratio, immersion time, and temperature. Phytochemical analysis revealed that the blended extract contained a higher concentration of beneficial compounds that enhance corrosion resistance. The optimal conditions identified through experimental design were a temperature of 30 °C, an 80% : 20% inhibition volume ratio, a 1.0 M acid concentration, and a duration of 9 days, yielding an impressive 98.28% inhibition efficiency. Polarization studies indicated that the extract acts as a mixed-type inhibitor. Adsorption analysis showed that the blended extract’s interaction with the aluminum surface conformed best to the Langmuir adsorption model. The calculated Gibbs free energy of adsorption (ΔG_ads) ranged from –16.73 to –22.73 kJ mol⁻¹, suggesting that the adsorption process is spontaneous. The activation energy (E_a) indicated that the process is characterized by physisorption, while the enthalpy change (−ΔH) pointed to an exothermic reaction. Additionally, the entropy change (ΔS) suggested a significant increase in disorder. Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) analyses confirmed that a more effective protective layer formed on the aluminum surface. In conclusion, the blended extract from guava and mango leaves demonstrates considerable potential as an environmentally friendly alternative to traditional industrial inhibitors, offering significant corrosion protection for aluminum alloys.

Concrete-reinforced structures are widely used in construction due to their strength and durability. However, the reinforcement steel within concrete is susceptible to corrosion, which can compromise the structural integrity of the entire system.^72,73  The primary corrosion issues in concrete-reinforced structures include chloride-induced corrosion, carbonation, and rust staining. Chloride-induced corrosion occurs when chloride ions from de-icing salts, seawater, or other sources penetrate the concrete and reach the embedded steel reinforcement. Chlorides disrupt the protective oxide layer on the steel surface, leading to corrosion and the formation of rust. As the steel corrodes, it expands, causing the surrounding concrete to crack and spall. This can significantly reduce the load-bearing capacity and durability of the structure. Carbonation is another major corrosion issue in concrete-reinforced structures. Carbon dioxide from the atmosphere reacts with calcium hydroxide in the concrete, forming calcium carbonate. This reaction lowers the pH of the concrete, reducing its alkalinity and weakening the protective layer around the steel reinforcement. As a result, the embedded steel becomes more susceptible to corrosion. Rust staining is a visible sign of corrosion in concrete-reinforced structures. As the steel reinforcement corrodes, rust can migrate through the concrete and create reddish-brown stains on the surface. Rust staining is often an indicator of underlying corrosion issues and can affect the aesthetic appearance of the structure.

To mitigate corrosion in concrete-reinforced structures, several strategies can be employed. One effective approach is the use of corrosion-resistant reinforcement materials. Epoxy-coated steel bars or stainless-steel reinforcement can provide enhanced resistance to corrosion and improve the longevity of the structure. Additionally, using non-corrosive alternatives such as fiber-reinforced polymers (FRPs) can further reduce the risk of corrosion. Another strategy is to apply protective coatings to the concrete surface.^74,75  Coatings such as sealers and membranes can prevent the ingress of moisture and chlorides, reducing the risk of corrosion. Additionally, applying a high-quality concrete mix with low permeability can help minimize the penetration of corrosive agents and protect the steel reinforcement. Regular maintenance and inspection are also critical for managing corrosion in concrete-reinforced structures. Routine inspections can help identify early signs of corrosion, such as cracks or rust staining, allowing for timely repairs and preventive measures. Implementing a comprehensive maintenance plan that includes surface cleaning, coating application, and monitoring can help address corrosion issues and extend the lifespan of the structure. Liu et al.⁷⁶  discussed the corrosion resistance of HRB400 rebar in environments that simulate the conditions found in concrete pore solutions, particularly focusing on the presence of chloride (Cl⁻) and sulfate (SO₄²⁻) ions. Given the increasing concern over the durability of reinforcing steel in concrete structures, particularly due to corrosion-induced degradation, understanding how various elements can enhance resistance is crucial. The study employed a series of electrochemical tests to quantify the corrosion rates of HRB400 rebar in solutions with varying concentrations of sulfate ions. The results indicated a clear trend: as the sulfate concentration increased, the corrosion rates of the rebar also rose. This behavior can be attributed to sulfate ions, which are known to exacerbate corrosion processes, particularly in the presence of moisture. However, the introduction of chromium and rare earth elements into the rebar composition had a pronounced effect on mitigating these corrosion rates. The data showed that, with the addition of Cr and RE, both the corrosion rates and the passive current density decreased significantly, especially in high sulfate environments. This suggests that these elements play a critical role in enhancing the protective qualities of the rebar. The mechanism behind this improvement in corrosion resistance is primarily linked to changes in the surface passivation film that forms on the rebar. This passivation film acts as a barrier, preventing aggressive ions from reaching the underlying metal. The presence of Cr and RE seems to promote a more stable and protective passivation layer, which is less susceptible to degradation under corrosive conditions. Furthermore, the study highlighted a synergistic effect when both Cr and RE were present together. The combination of these elements proved to be more effective at reducing localized corrosion risks compared to the use of Cr alone. Localized corrosion, such as pitting, can lead to severe structural failures in reinforced concrete, making this finding particularly significant. The ability of the Cr/RE combination to enhance corrosion resistance not only improves the longevity of HRB400 rebar but also underscores the potential benefits of optimizing alloy compositions for enhanced performance in corrosive environments. Murthy et al.⁷⁷  explored the use of machine learning techniques to predict the half-cell potential (HCP) values of cathodically protected reinforced concrete slabs exposed to chloride ingress. Specifically, the research involved the casting of six classes of concrete slabs, each embedded with centrally positioned pure magnesium (Mg) anodes and constructed with dimensions of 1000 mm × 1000 mm × 100 mm. The input variables for the predictive models included the distances of the measurement points in both the x and y directions (Dist x and Dist y), relative humidity (RH), temperature, the age of the concrete in days, and the specific class of the slab. For each slab class, three specimens were cast, and the average HCP value was computed as the output. Throughout the study, a total of 80 HCP measurements per slab were recorded daily over a span of 270 days, allowing for the generation of a robust prediction model. To validate the experimental dataset, the researchers applied several machine learning algorithms, including linear regression, kernel ridge regression, stochastic gradient descent, support vector machines, decision trees, random forests, gradient boosting, and light gradient boosting machine (LGBM). Among these models, LGBM demonstrated superior performance across all evaluation metrics. The results indicated that LGBM achieved an impressive R-squared score of 0.9828, along with a low mean square error (0.0015), root mean square error (0.0386), and mean absolute error (0.0220). It also scored high on the a-10 index (0.8007) and a-20 index (0.8987), confirming its effectiveness as the optimal choice for this dataset. Furthermore, sensitivity analysis conducted for the LGBM model revealed that the ‘age of concrete’ was the most significant factor influencing the predictions. In contrast, temperature and relative humidity had relatively lower impacts, while the other variables were found to contribute negligibly to the model’s output.^78–83 

Wattanavichien et al.⁸⁴  explored the innovative use of polyethylene terephthalate (PET) plastic waste as a fine aggregate in concrete production, a practice that could significantly address pressing environmental issues. The dual challenge of depleting natural resources, particularly sand—which is a primary ingredient in traditional concrete—and the rising accumulation of non-biodegradable plastic waste necessitates alternative solutions that promote sustainability. Concrete is essential in the construction industry, yet its production is resource-heavy and contributes significantly to greenhouse gas emissions. The scarcity of natural aggregates, like sand, makes it imperative to explore sustainable materials that can replace them without compromising concrete performance. The incorporation of municipal plastic waste, particularly in the form of PET, emerges as a promising solution that not only conserves natural resources but also mitigates environmental impacts associated with plastic disposal. In this study, the researchers focused on fine PET aggregates characterized by both uniform and non-uniform shapes, with sizes ranging from 2.36 to 4.75 mm. They formulated concrete mixtures by replacing fine natural aggregates with PET at varying percentages: 0%, 30%, and 50%. A consistent water-to-cement ratio of 0.40 was maintained across all mixtures to ensure comparability. The results revealed some trade-offs. The inclusion of PET aggregates resulted in a decrease in compressive and splitting tensile strengths compared to the control specimens without any PET. This reduction in mechanical properties is a crucial consideration for construction applications, as strength is a key performance criterion for concrete. However, the findings also highlighted significant advantages at the 30% replacement level. The PET-modified concrete exhibited enhanced resistance to chloride ion penetration—an important property since chloride ingress is a major factor contributing to the corrosion of steel reinforcement in concrete structures. Specifically, the chloride resistance improved by 13% for concrete with uniform PET aggregates and 12% for those with non-uniform aggregates. This enhanced chloride resistance is particularly valuable, as it indicates a better ability of the concrete to withstand harsh environmental conditions, which can prolong the lifespan of structures and reduce maintenance costs. Additionally, the bond between the cement paste and PET particles was found to be stronger when 30% of the fine natural aggregate was replaced, further suggesting that PET aggregates can contribute positively to the durability of concrete. Overall, this research not only characterizes the material properties of concrete incorporating PET but also illustrates a viable method for recycling municipal plastic waste. By demonstrating that PET can be effectively used in concrete production without severely compromising its performance—while improving certain durability aspects—this study paves the way for more sustainable construction practices. Such innovations could lead to reduced reliance on natural aggregates and contribute to efforts in waste management, aligning with broader goals of environmental sustainability in the construction industry.

Kim et al.¹⁴  explored the effectiveness of electrochemical deposition treatment (EDT) as a comprehensive rehabilitation method for addressing corrosion-induced deterioration in reinforced concrete across various severity levels. Corrosion in reinforced concrete structures occurs in three main stages: initiation (de-passivation of steel), propagation (active corrosion), and acceleration (formation of surface-breaking cracks). Each of these stages presents different challenges for repair and rehabilitation. To test the feasibility of EDT, the researchers conducted a series of accelerated corrosion experiments that simulated these stages of corrosion. Concrete samples with varying levels of damage were treated using EDT, which involved the use of a magnesium chloride (MgCl₂) solution as the electrolyte. The experiments were divided into three phases, each focusing on a specific aspect of the EDT process. In the first phase, the study assessed the effect of different concentrations of MgCl₂ (ranging from 0 to 3.0 M) on corrosion prevention and mitigation during the early stages of corrosion. In the second phase, they investigated the influence of charging time in the EDT process (from 0 to 7 days) on the rehabilitation performance. The third phase examined the configuration of pre- and post-treatment processes, including the application of a sodium hydroxide (NaOH) solution following EDT, to enhance the crack-repairing capabilities of the method (Figure 1.5). The results indicated that EDT is highly effective in both preventing and mitigating corrosion during the initiation and propagation phases of corrosion. It also showed promising results in repairing surface-breaking cracks that form during the acceleration phase of corrosion. Specifically, higher concentrations of MgCl₂ and longer charging times in EDT were associated with improved corrosion resistance in the treated concrete. Furthermore, the application of NaOH in the post-treatment phase significantly enhanced the ability of EDT to repair cracks, resulting in better overall rehabilitation performance.

The financial costs associated with corrosion are substantial and multifaceted. They encompass direct expenses related to repair and replacement, as well as indirect costs such as productivity losses and decreased property value.^85–87  The economic burden of corrosion affects various sectors, including transportation, construction, and manufacturing, leading to significant financial implications. Direct costs related to corrosion include expenditures for maintenance, repairs, and replacements of corroded infrastructure and equipment. For example, the repair of corroded bridges and roads requires substantial financial investment, often involving extensive labor and material costs. In the United States alone, it has been estimated that corrosion-related maintenance and repairs cost billions of dollars annually. Similar financial burdens are observed globally, with countries investing heavily in infrastructure upkeep to address corrosion issues. In addition to maintenance and repair costs, the replacement of corroded assets can be particularly expensive. When infrastructure or equipment reaches a stage where it is no longer viable to repair, replacement becomes necessary. This process involves not only the cost of new materials and construction but also potential disruptions to services and operations. For instance, the replacement of a major bridge or a section of a railway can lead to significant downtime and inconvenience for users, further exacerbating the economic impact. Indirect costs associated with corrosion are also substantial. One notable example is the loss of productivity resulting from the downtime of equipment and infrastructure. Corroded machinery or transport systems can lead to operational disruptions, impacting industries and services reliant on these assets. For example, in the energy sector, corrosion-related failures in pipelines or refineries can cause significant production losses, affecting energy supply and prices. Another indirect cost is the decrease in property value due to visible corrosion damage. Properties with deteriorated infrastructure or aesthetic issues related to corrosion may experience reduced market value, impacting owners and investors. This can have cascading effects on local economies, particularly in areas heavily reliant on real estate and property development.

Corrosion poses serious safety concerns, which can have catastrophic consequences if not adequately addressed. The deterioration of infrastructure and equipment due to corrosion can lead to structural failures, accidents, and even loss of life. Ensuring safety in the presence of corrosion requires vigilance, regular maintenance, and proactive measures to prevent potential hazards. Structural failures due to corrosion are among the most critical safety concerns. Corroded steel beams, bridges, and other structural elements can lose their load-bearing capacity, leading to collapses or other failures. High-profile incidents such as bridge collapses or building failures often bring attention to the safety risks associated with corrosion. For example, the 1967 collapse of the Silver Bridge in the United States was attributed to corrosion-related issues, resulting in the loss of 46 lives and highlighting the severe consequences of inadequate maintenance. In addition to structural failures, corrosion can also contribute to safety hazards in industrial and transportation systems. Corroded pipelines, storage tanks, and machinery can lead to leaks, spills, and explosions. In the chemical industry, corrosion-related failures in equipment can result in hazardous chemical release, posing risks to workers and surrounding communities. Similarly, corrosion in aircraft components can lead to mechanical failures, jeopardizing aviation safety. Addressing safety concerns requires a comprehensive approach that includes regular inspections, monitoring, and maintenance. Implementing rigorous safety standards and protocols can help identify and mitigate corrosion-related risks before they escalate into serious issues. Moreover, investing in corrosion-resistant materials and protective coatings can enhance the safety of infrastructure and equipment, reducing the likelihood of failures and accidents.

The long-term economic implications of corrosion extend beyond immediate financial costs and safety concerns. Corrosion affects the sustainability and resilience of infrastructure, influencing economic stability and growth. Addressing these implications involves understanding the broader impact of corrosion on economic development, resource allocation, and future investments. One significant long-term economic implication of corrosion is its impact on infrastructure sustainability. As infrastructure deteriorates due to corrosion, the need for ongoing maintenance and replacement increases. This can strain public and private budgets, diverting resources from other critical areas such as education, healthcare, and social services. For example, governments may need to allocate substantial funds to infrastructure upkeep, potentially impacting their ability to invest in other sectors. Moreover, the degradation of infrastructure due to corrosion can affect economic growth and development. Well-maintained infrastructure is essential for supporting economic activities, including transportation, trade, and commerce. Corroded roads, bridges, and public utilities can hinder economic efficiency, leading to increased transportation costs, delayed shipments, and reduced productivity. In turn, this can affect business competitiveness and economic performance at both local and national levels. Corrosion also has implications for future investments in infrastructure and technology.^88–98  The need to address corrosion-related issues can influence investment decisions, particularly in industries that rely heavily on infrastructure and equipment. For example, the energy sector may face challenges in securing investments if corrosion-related risks are perceived as high. Additionally, the cost of implementing advanced materials and technologies to mitigate corrosion can impact investment decisions and long-term planning. Addressing the long-term economic implications of corrosion requires a proactive and strategic approach. Investing in corrosion prevention and control measures, such as advanced materials, coatings, and monitoring technologies, can help reduce the overall economic impact. Furthermore, adopting best practices in infrastructure design, construction, and maintenance can enhance resilience and sustainability, ensuring that infrastructure continues to support economic growth and development.

The impact of corrosion on infrastructure and industrial systems is profound. Financially, corrosion leads to significant direct and indirect costs, including maintenance, repairs, and replacement of corroded assets. These expenses extend beyond immediate financial outlays to affect productivity, property value, and overall economic stability. Safety concerns associated with corrosion are equally critical, as deterioration of structural elements and equipment can lead to catastrophic failures, accidents, and loss of life. The long-term economic implications are also significant, affecting infrastructure sustainability, economic growth, and future investment decisions. Despite the considerable advancements in corrosion science and technology, challenges remain. The need for effective corrosion management strategies that balance cost, performance, and environmental impact is ever-present. Advances in understanding corrosion mechanisms and developing new materials and coatings offer hope for mitigating these issues. However, the complexity of corrosion processes necessitates continued research to develop more effective, sustainable, and cost-efficient solutions. Looking forward, several key areas of research are poised to advance the field of corrosion science and management. One promising direction is the development of advanced materials with enhanced corrosion resistance. Researchers are exploring new alloys, composites, and coatings designed to withstand aggressive environments and extend the lifespan of critical infrastructure. For example, high-performance polymers, nanomaterials, and advanced coatings offer potential solutions for mitigating corrosion in challenging environments. The integration of these materials into infrastructure design and maintenance practices could significantly reduce corrosion-related costs and improve safety. Another important area of research is the advancement of corrosion monitoring and assessment technologies. Traditional methods of inspection and monitoring, such as visual inspections and periodic testing, are often labor-intensive and may not detect early signs of corrosion. Innovative technologies, such as sensors, smart coatings, and real-time monitoring systems, offer the potential for more accurate and timely detection of corrosion. These technologies can provide valuable data for predictive maintenance, enabling proactive interventions before significant damage occurs. The development and implementation of these advanced monitoring systems will enhance the ability to manage corrosion effectively and reduce the associated risks.

In addition, there is a growing focus on understanding the environmental impacts of corrosion and developing sustainable solutions. Research into the environmental effects of corroded materials, including the release of pollutants and degradation products, is essential for developing strategies that minimize environmental harm. Sustainable approaches to corrosion management, such as the use of eco-friendly coatings and materials, can help reduce the environmental footprint of corrosion-related activities. Integrating environmental considerations into corrosion research and practice will support the development of more sustainable infrastructure and technologies. Collaboration between researchers, industry professionals, and policymakers is crucial for advancing corrosion research and addressing its challenges. Interdisciplinary approaches that combine materials science, engineering, environmental science, and economics can provide a comprehensive understanding of corrosion issues and lead to innovative solutions. Partnerships between academia, industry, and government agencies can facilitate the translation of research findings into practical applications and inform policy decisions related to corrosion management and infrastructure maintenance. Furthermore, education and training play a vital role in advancing corrosion research and management. Developing educational programs and training initiatives that focus on corrosion science, materials engineering, and maintenance practices can help build a skilled workforce capable of addressing corrosion challenges. Promoting awareness of corrosion issues and best practices among engineers, technicians, and decision-makers will contribute to more effective corrosion management and ensure the continued development of innovative solutions.