Weathering Steel in Civil Engineering and Architecture: A State-of-the-Art Review

Abstract

Weathering steel has a fascinating history that dates back to the 1930s, and its evolution has left an indelible mark on various industries, from railways to architecture. Thanks to its high corrosion resistance with respect to conventional steel, weathering steel has assumed key roles in structural applications (buildings, bridges, railways, etc.), non-structural elements (facades, decorative elements), and installations at archaeological sites (retrofitting, sculptures), especially when exposed to aggressive environments. This paper is aimed at providing a state-of-the-art overview of the application of weathering steel in architecture and engineering applications, focusing on the development of scientific and technical knowledge on the subject and on future directions arising from current utilization. An evolution timeline of weathering steel-based constructions and their structural/typological classification is illustrated and discussed. In such a context, pros and cons related to maintenance aspects of weathering steel structures are also discussed, accounting for costs relative to structural and nonstructural maintenance and those related to environmental sustainability with respect to other traditional constructions. From a structural design point of view, the rules and recommendations provided by the main national and international standards—concerning material properties and types, design, and checks on structural members made with weathering steel—are analyzed, critically discussed, and compared, also with the aim of identifying possible gaps in comparison with other construction materials.

1. Introduction

Weathering steel, also known by its trade name “Corten” (corrosion and tension steel), is a high-strength, low-alloy steel that was developed by Vereinigte Stahlwerke AG in Germany in 1928 and by the United States Steel Corporation in 1933 when it was facing a unique challenge: the need for rugged, corrosion-resistant steel for railway coal wagons. This was an era when America’s railways and collieries demanded materials able to tolerate the harshest conditions. Thus, in response to this demand, weathering steel was introduced. In this way, weathering steel found its initial purpose in the world of railway transportation [1,2,3]. Investigations conducted in 1936 [2,4] demonstrated that high-tensile steels offered many advantages with respect to the structural nickel-based steel used in ordnance applications. These included excellent weldability, tensile stress strength, ductility, and toughness. However, its patented composition and high cost were considered drawbacks. Since the first applications, the success of weathering steel has been evident due to its lightness and superior resistance to impact and corrosion compared to conventional steels [3,4].

From the 1960s onward, engineers and architects expanded the application of weathering steel in the field of civil engineering, exploiting its improved corrosion resistance. It was widely adopted in various construction contexts [1,5,6,7,8], and soon weathering steel became synonymous with innovative and visually striking architectural designs.

Weathering steel is the result of exceptional properties coming from the manipulation of alloying elements during the production process. Elements such as chromium, copper, silicon, and phosphorus are added to create this steel [9,10,11,12,13]. This combination provides resistance to corrosion because of the development of a protective rust layer (known as iron oxide) that forms and stabilizes over time under favorable weather conditions [10,11,12,14]. Unlike the porous oxide layer found in conventional steels, this rust layer prevents moisture retention and inhibits further corrosion, resulting in a distinctive appearance and long-term durability. In principle, this makes the material maintenance-free [10,11,14].

This latter aspect incentivized the use of weathering steel and its growth in various technical sectors, industry, and construction. It has become an archetypal material for engineers, architects, manufacturers, landscapers, urban planners, and artists, whose choices were often limited due to its high cost with respect to other traditional materials (e.g., reinforced concrete or masonry).

Another benefit coming from the application of weathering steel is cost-effectiveness over time; although weathering steel is slightly more expensive than conventional steel, savings from the elimination of a paint system offset the additional material cost [11,12].

From an aesthetic standpoint, one of the main attractions of weathering steel for both structural and non-structural applications is its ability to blend naturally with its surroundings. Its appearance improves over time as a stable oxide layer forms, usually resulting in a rich, dark-brown hue [7]. The best performance is achieved in rural and urban environments, where cycles of wetting and drying by clean rainwater foster the development of a dense, tightly adhering oxide layer [6,15]. In contrast, weathering steel-based construction in environments with high concentrations of industrial pollutants or marine conditions should be avoided [9,16,17].

Beyond its well-known durability and corrosion resistance, weathering steel is increasingly expected to perform reliably under extreme conditions such as strong winds, seismic events, and progressive collapse. Recent research highlighted the importance of incorporating innovative structural systems that enhance ductility and energy dissipation, effectively aligning sustainability with disaster resilience [18]. This evolution marks a paradigm shift in which sustainable construction must also meet rigorous safety and reliability design standards, especially in critical infrastructure like bridges. Consequently, combining structural resilience with eco-efficiency has become a fundamental requirement for the next generation of weathering steel applications [18,19].

This paper provides a state-of-the-art review of the application of weathering steel in architecture and civil engineering applications, focusing on the development of scientific and technical knowledge on the subject and future directions arising from current utilization. The paper, which emphasizes novel insights and the state of research advancements, serves as a baseline for expert researchers working in the field of weathering steel and/or related fields, facilitating better cross-fertilization of ideas globally and accelerating future research.

The paper Is organized as follows. Section 2 gives an overview of the technical literature and a timeline of the development and use of weathering steel in civil engineering and architecture. Section 3 deals with the standards available worldwide, containing technical rules and recommendations on the use of weathering steel in construction. Section 4 summarizes the application of weathering steel in the fields of civil engineering and architecture. Section 5 focuses on particular issues regarding the inspection, monitoring, and maintenance of weathering steel bridges. Section 6 reports pros and cons of weathering steel in engineering and architecture applications. Section 7 deals with future developments and trends, and Section 8 concludes the paper.

2. Technical Literature Overview and a Journey Through Time

This section depicts the current state of knowledge in the scientific and technical literature. It is conceived as a journey through the history of weathering steel—from its beginnings in the 1930s up to today (2025). Therefore, this section is divided into separate sub-sections covering each decade. Nevertheless, a preliminary analysis exploiting the capabilities of existing bibliographical databases is presented below.

Relevant literature data available from the Scopus dataset [20] were analyzed in order to identify approaches, methods, and gaps in existing research to construct and visualize a bibliometric network using the VOSviewer application (Figure 1).

With this aim, the keyword “weathering steel” was entered into the search engine using the article title, abstract, and keywords. A total of 1662 documents were found, spanning from the year 1968 (the oldest) to 2025. All these documents were exported in .csv format, including citation information, abstract, and keywords. Then, VOSviewer was used to create a new map based on the bibliographic data by selecting Scopus as the data source and choosing the “co-occurrence” analysis type and “all keywords” from among the available options. To improve the investigation and reduce redundancy, repeated keywords-such as “weathering steel” and “steel” were removed.

As shown in Figure 2a,b, “atmospheric corrosion” and “steel bridges” stood out as the main clusters after selecting these keywords in the final step in VOSviewer (by repeating all the steps described above), highlighting the importance of corrosion in the study of weathering steel and its main application (steel bridges made of weathering steel) over the past seven decades.

Based on data from the bibliometric network, the relevant topics to be addressed included corrosion resistance, atmospheric corrosion, rust layers, high-strength steel, steel structures, weathering steel bridges, and fatigue testing (see Figure 1 and Figure 2). Therefore, the following sections trace the development and evolution of our understanding of weathering steel over several decades, highlighting its properties, applications, and challenges.

2.1. Early Developments (1930s)

This period marks the birth of weathering steel, driven by explorations into the corrosion and wear resistance of ferrous alloys, initially for industries like oil. Research focused on the formation and properties of protective films on different steels, emphasizing the importance of chemical composition and heat treatment [4]. The performance of steel in various corrosive environments, such as soils, salt water, and sour crude oil, was assessed. Weathering steel, referred to as high-tensile steel, was found to be a valid alternative to nickel-based structural steel for ordnance applications, offering advantages such as good weldability, formability, high ductility, and low content of strategic materials [2,3,4]. Although it corrodes more rapidly at first, this initial corrosion is more uniform, potentially extending the service life of the steel plates. The corrosion resistance of a metal depends on both the environment and the material’s intrinsic properties. Weathering steel was recognized for its superior resistance to atmospheric corrosion compared to ordinary carbon steel, significantly extending its service life [3]. It was widely used in railroad and other types of equipment where lightweight materials are advantageous. Its atmospheric service life was reported to be twice that of copper steel and approximately five times that of plain carbon steel. However, it was emphasized that corrosion resistance must be evaluated under precise and specific conditions. This period saw significant effort to develop new steels for industries such as oil and defense, with corrosion being identified as the central issue. Solutions involved modifying steel composition and improving the understanding of protective surface film mechanisms.

2.2. Employment in the Railway Industry (1940s)

In this decade, weathering steel emerged as a promising material for the railway industry, particularly for freight wagons. Its application in railroad structures was recognized as one of its earliest uses. By 1950, weathering steel was chosen as a primary material for freight wagon bodies, driven by cost considerations and the need for design improvements [21]. Although not yet widely adopted, its corrosion resistance and reduced maintenance requirements were quickly recognized as key advantages. The 1940s were a critical period for its development, laying the groundwork for expanded use in subsequent decades. Weathering steel was also used in the construction of locomotives, including frames, body members, and panels, contributing to a significant reduction in weight.

2.3. Focus on Corrosion Problems and High-Strength Steels (1950s)

The 1950s were characterized by a particular interest in corrosion problems, with an emphasis on understanding their causes to develop preventative measures [10,22]. Mitigating damage and prolonging infrastructure lifespan became key objectives, leading to the proposal and use of high-strength, low-alloy steels [12]. Corrosion represented a significant economic cost across industries, including the railway industry. Corrosion control strategies included protective coatings, corrosion-resistant metals (alloys) such as weathering steel, and corrosion inhibitors [10,11,12]. The development of high-strength, low-alloy steels was driven by the need for higher allowable stresses and lighter or thinner structural sections. General requirements for these steels included strength, ductility, and weldability [10]. The chemical composition was balanced to optimize strength and weldability, with elements like copper enhancing resistance to atmospheric corrosion [10,12]. This period provided historical perspective on corrosion problems and the efforts made to develop improved materials for structural engineering. High-strength, low-alloy steels represented a significant advance toward lighter, more durable, and corrosion-resistant structures, emphasizing the need for careful consideration of the composition, weldability, and application.

2.4. Understanding the Role of the Protective Layer (Patina) (1960s)

Corrosion remained a relevant issue in the 1960s. Weathering steel was noted for its ability to form an adherent oxide layer, reducing the corrosion process in atmospheric environments [6,7]. Research on the oxidation of low-alloy steels highlighted the influence of elements like chromium, silicon, and aluminum on the formation of protective oxide layers [8,23]. Atmospheric corrosion of copper-containing steels was also investigated, analyzing copper as a potential alloying element to enhance corrosion resistance [13]. It was definitively established that corrosion is a complex problem requiring multidisciplinary knowledge, and that proper material selection and design are crucial to its prevention. Improving education and awareness about corrosion among technicians was deemed essential to avoid costly failures. Further research and development were concluded to be necessary to better understand corrosion mechanisms and to develop new prevention and mitigation techniques.

2.5. Alloy Optimization and Environmental Influences on the Atmospheric Corrosion of Weathering Steel (1970s)

The application of weathering steel in different sectors continued to expand. Studies focused on alloy additions to meet demands in environments where weathering steel had not yet exhibited ideal behavior. Small additions of copper, molybdenum, silicon, and chromium were shown to significantly reduce the corrosion rate of weathering steel in atmospheric environments [24]. In contrast, the presence of manganese was found to increase the tendency toward pitting corrosion [25]. The formation of a protective oxide layer (rust) was observed as crucial, with its density, adhesion, and chemical composition being directly influenced by the steel’s chemical composition [24,26]. Atmospheric corrosion was significantly affected by environmental factors such as humidity, temperature, and contaminants like sulfur dioxide (SO₂) and chlorides. Seasonal variations and meteorological conditions played major roles [27]. Electrochemical techniques were applied to evaluate corrosion resistance [28]. A model developed by Legault [29] made it possible to predict long-term corrosion behavior based on short-term data. The corrosion behavior of mild steel in contact with dissimilar metals was also studied, showing that such coupling can accelerate corrosion. However, some metals (e.g., Mg, Zn) provided cathodic protection, while others (e.g., Cu, Sn, Ni) increased the corrosion rate [30]. In summary, the atmospheric corrosion of steel was described as a complex process influenced by multiple interrelated factors, including the steel composition, environmental conditions, and the presence of dissimilar metals.

2.6. Increasing Use and Fatigue Understanding (1980s)

During this period, the use of weathering steel in bridges expanded globally. Studies addressed its behavior with respect to corrosion and the environmental factors influencing durability [31,32]. Corrosion resistance was emphasized as being dependent on the formation of protective corrosion products, influenced by wetting and drying cycles, steel composition, and atmospheric conditions [16,17]. Techniques such as infrared and Raman spectroscopy were used to analyze corrosion products, revealing oxides such as Fe₂O₃, FeOOH, and magnetite [33,34,35]. Electron microscopy revealed the morphology of oxide phases, showing characteristic layers such as y-Fe₂O₃ H₂O, a-FeOOH, and δ-FeOOH [35,36]. Quantitative methods were developed to classify patina conditions based on the mechanical strength and thickness of the rust film [37,38]. The behavior of phosphorus during protective patina formation was also investigated, providing insights into how specific elements enhanced corrosion resistance. This knowledge was essential for predicting the long-term performance of weathering steel structures and for developing effective protection strategies [39,40,41]. Fatigue testing showed that exposure to weathering conditions reduced the service life of steel, influenced by factors such as weld quality and profiles. The presence of salt water accelerates corrosion and can further decrease fatigue strength. Fatigue strength and allowable stress range were found to decrease as a function of exposure time and the presence of saline environments [42,43,44].

2.7. Superior Performance and Layer Details (1990s)

Weathering steel was widely used in structures due to its superior atmospheric corrosion resistance compared to carbon steel, attributed to alloying elements (copper, chromium, nickel, silicon, phosphorus) that promote the formation of a protective oxide layer [45,46,47]. Environmental factors such as climate, atmospheric pollutants (e.g., sulfur dioxide), and sea salts were found to significantly influence corrosion [48]. Weathering steels were observed to form a thinner, denser oxide layer compared to the porous rust typically seen on exposed carbon steels [45]. The rust structure on weathered steels showed distinct light and dark regions; the light regions, consisting of an outer layer of hematite and magnetite, were suggested to be important for corrosion protection [49]. Electrochemical studies indicated that weathering steel is more resistant to SO₂-induced atmospheric corrosion than carbon steel [50]. The chromium present in goethite also contributed to the formation of a stable protective layer [51]. The formation of a protective oxide layer, enriched with alloying elements and nanoscale goethite, was identified as a key factor in ensuring the long-term durability of weathering steels. Environmental parameters significantly influenced both the corrosion process and the structure of the resulting oxide. Stress cycles in humid freshwater or saltwater environments resulted in a notable decrease in fatigue strength.

2.8. Bridge Focus (2000s)

This period provided comprehensive overviews of weathering steel corrosion, focusing on design, construction, monitoring, and maintenance methods, particularly for weathering steel bridges. Advantages in bridge construction included low maintenance requirements, reduced costs, shorter construction times, improved aesthetics, reduced environmental impact, and longer service life [52]. However, weathering steel was found to be unsuitable for use in marine environments, areas exposed to road salt spray, immersion or burial conditions, or industrial atmospheres polluted with SO₂ [52,53]. Design considerations for bridges included potential thickness reduction due to corrosion, ensuring consistent dry/wet cycles, managing water runoff, and ensuring material compatibility [54]. Sandblasting was recommended to promote the formation of a uniform patina [52]. A major issue observed in existing bridges was leakage at expansion joints, which caused saltwater to flow over girders [52]. Careful detailing of bolted connections was necessary to minimize corrosion risks [52]. Risk-based design and maintenance systems were developed for bridges, including computer-aided corrosion prediction, structural monitoring, and repair planning tools [55]. One method for selecting weathering steel for bridges considered environmental corrosivity and steel characteristics [56]. Advances in analytical methods, such as Mössbauer spectroscopy, provided valuable tools for corrosion characterization and prediction [57]. Appropriate steel selection and a thorough understanding of the exposure environment were essential for ensuring long-term performance.

2.9. Accelerated Research and Patina Analysis (2010s)

Research on weathering steel intensified during this decade, focusing on identifying the optimal steel composition for different environmental conditions. It was increasingly recognized as a cost-effective option for public asset management, particularly in bridge construction, due to its potential to reduce maintenance cost [58,59,60]. The chemical composition typically included elements such as carbon, silicon, manganese, phosphorus, sulfur, copper, nickel, and chromium [61,62]. These steels develop a protective patina over time [63,64], whose performance can be evaluated using the Protective Ability Index (PAI), which considers the proportion of goethite and lepidocrocite in the oxide layer [63]. Electrochemical Impedance spectroscopy (EIS) was demonstrated to be an accurate, non-destructive technique for monitoring the protective effectiveness of the corrosion product layer. Microclimatic factors, such as chloride deposition from deicing salts, were shown to significantly influence the formation of corrosion products on weathering steel bridges [59,65]. Bridge performance was influenced by environmental conditions, design practices, and maintenance strategies [60,64,66,67,68]. Evaluation methods included measuring corrosion loss and product thickness, along with analyzing the protective capacity using techniques such as X-ray diffraction (XRD) and EIS [63,64,69,70,71,72]. Exposure to urban pollution and marine environments was found to lead to aesthetic issues [15,73,74,75,76]. Correlation models were developed to predict service life more reliably [77,78].

2.10. Effect of Corrosion on the Fatigue and Current Advances (2021–2025)

Recent studies have investigated the corrosion resistance, mechanical behavior, and oxide layer evolution of weathering steel using various analytical techniques (XRD, SEM, XPS, EIS). UPTOHERE It is used in various applications, including bridges, due to its ability to form a protective patina layer that reduces corrosion [79,80,81]. Patina formation depends on wetting and drying cycles [79]. However, in industrial or coastal environments, chlorides and contaminants can accelerate corrosion, transforming stable goethite into less protective akaganeite [79,82,83]. The composition of the oxide layer, steel microstructure, and environmental conditions influence corrosion resistance [79,84,85,86]. Adding elements like chromium, copper, and nickel can improve the protective properties of the oxide layer [82,85,87,88,89,90]. Weathering steel exhibits different crystalline phases in the patina, whose proportion influences protection [79]. A chromium-rich amorphous phase in the inner layer also contributes to improved corrosion resistance. In industrial environments, SO₂ contamination leads to specific rust formations [88]. Weathering steel is subject to corrosion fatigue, especially in critical welded joints in bridges. A Probabilistic Corrosion Fatigue (PCF) model can help predict deterioration in these structures, considering factors like heavy traffic and corrosive conditions [80,91]. The corrosion behavior and mechanical properties of weathering steel after corrosion damage can be examined by evaluating weight loss and mechanical properties [92,93].

Finally, recent research and applications highlight its growing adoption in sustainable buildings. For instance, a life-cycle analysis conducted by SWECO for the Swedish Transport Administration concluded that a footbridge constructed with weathering steel was approximately 25% more cost-effective over an 80-year period compared to a similar structure made of painted carbon steel, due to the elimination of painting and associated maintenance processes [94,95].

Moreover, from an architectural standpoint weathering steel also has found interesting applications in green buildings, harmonizing aesthetics and sustainability [96].

The use of high-strength weathering steel allows for lighter and more efficient designs, reducing material consumption and embodied carbon emissions. Studies by the Technical Research Centre of Finland (VTT) demonstrated that buildings constructed with weathering steel exhibit minimal overall corrosion rates under C2 and C3 atmospheric conditions, confirming its suitability for sustainable applications [94,97].

3. Structural and Key Material Features

The beginning of the 1930s marks a complete renewal in the approach to the production of special steels, driven by advances of the time. Starting in 1933, US Steel research engineers developed and marketed weathering steel, with characteristics as of 1937 available in [1,3,21]. Today, the ASTM International Standard includes four grades [98,99,100,101] of weathering steel, along with five relevant international standards and their corresponding grades [102,103,104,105,106], which will be explained in the following paragraphs.

Standards provide guidelines for the chemical composition, mechanical properties, fabrication requirements, and testing procedures of weathering steel materials. They ensure consistency and quality in the manufacture and use of weathering steel across various structural applications, including bridges, buildings, highway infrastructure, and outdoor sculptures. Adherence to these standards helps to ensure the long-term performance, durability, and safety of weathering steel structures in diverse environmental conditions. The standards for weathering steel are described below.

3.1. American Standards

The ASTM standards are widely recognized worldwide because they include high-strength and low-alloy structural steel. Over the years, four ASTM standards have focused their attention on weathering steels, namely A242, A588, A606, and A709.

All the ASTM standards are issued under the fixed designation A242 (as an example); the number immediately following the designation indicates the year of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval.

For each ASTM standard, the following key points must be taken into account (also listed in Table 1):

(a)

The chemical requirements (heat analysis) shall conform to the requirements prescribed in each specification, subject to the product analysis tolerances in Specification A6/A6M-24b, General Requirements for Rolled Steel Plates, Shapes, Sheet Piling, and Bars for Structural Use [107].

(b)

For methods of estimating atmospheric corrosion resistance of low-alloy steels, see Guide G101, Standard Guide for Estimating the Atmospheric Corrosion Resistance of Low-Alloy Steels [108].

(c)

When the steel is to be welded, it is assumed that a welding procedure suitable for the grade of steel and intended use or service will be utilized. Appendix X3 of Specification A6/A6M provides information on weldability [107].

3.1.1. ASTM A242

The specifications ASTM A242-79 and A242/A242M-24 cover high-strength low-alloy structural steel shapes, plates, and bars for welded, riveted, or bolted construction, intended primarily for use as structural members where weight savings or added durability are important. This specification is limited to material up to 4 in. (100 mm), inclusive, in thickness [98,109].

The complete document history of this specification covers 23 editions, from its first introduction in 1979 to the most recent update in 2024. This data can be found at www.document-center.com (accessed on 7 February 2025) [110] and www.astm.org (accessed on 7 February 2025) [111]. This standard has undergone several updates over the years, with significant revisions. Each revision aimed to refine material properties, testing methods, and other specifications to align with advancements in steel production and technology.

The tensile strength properties of the ASTM A242-particularly from 1979 to the latest edition in 2024-have evolved over time, reflecting advances in materials science, manufacturing processes, and the need for more precise and consistent performance in structural applications. While the tensile requirements of ASTM A242 have remained relatively stable throughout this period [98,109,110,111,112,113] (see values on Table 1), the standard has continued to evolve to maintain its relevance by adapting to improvements in testing methods, production technology, and performance expectations. The key takeaway is that the balance between tensile strength and weathering resistance has stood the test of time, with A242 continuing to be a crucial material for infrastructure exposed to the elements, particularly in the construction of bridges, buildings, and outdoor structural components.

Given its high tensile strength and corrosion resistance, ASTM A242 is primarily used in applications where durability and resistance to weathering are crucial. Common uses include the following: bridges, due to its ability to resist corrosion over time, particularly in high moisture or coastal environments; the structural components of buildings, especially in regions where environmental exposure can accelerate material degradation; and last but not least, in railway coal cars, thanks to its long-lasting performance in outdoor environments. See Table 2.

3.1.2. ASTM A588

The specification ASTM A588-88 and A588/A588M-24 covers high-strength low-alloy structural steel shapes, plates, and bars for welded, riveted, or bolted construction, intended primarily for use in welded bridges and buildings where weight savings or added durability are important. This specification is limited to material up to 8 in. (200 mm), inclusive, in thickness [99,114,115,116,117,118,119].

This specification includes 19 editions since the first introduction in 1988 to the last update in 2024. See www.document-center.com (accessed on 7 February 2025) [110] and www.astm.org (accessed on 7 February 2025) [111]. Starting with the 2010 version, Grade C was removed from Table 1, Chemical requirements (Heat analysis), of the document [118,119].

Initially, ASTM A588 was developed for applications requiring resistance to atmospheric corrosion in bridge and steel construction. Its weathering properties proved especially valuable for structures in exposed environments. For instance, it became widely used in bridges, as the material offered not only durability but also cost savings due to reduced need for maintenance and painting [116,119].

The advancements in ASTM A588 over the years have turned it into a leading choice for structural steel in challenging environments. The tensile strength, yield point, and elongation values are provided in Table 1. From its early role as a solution to corrosion issues to its current status as a high-performance, sustainable material, the standard has continually evolved to meet the needs of the construction industry. Key developments—including enhanced corrosion resistance, improved mechanical properties, advanced fabrication compatibility, and increased global usage-have firmly established ASTM A588 as a preferred material for a wide range of structural applications, as shown in Table 2. Looking ahead, continued innovation in design, sustainability, and fabrication technologies will likely maintain ASTM A588´s relevance and leadership in the field of structural/material science.

3.1.3. ASTM A606

The specification ASTM A606 covers high-strength, low-alloy cold-rolled sheet and strip in cut lengths or coils; hot-rolled sheet and strip steel in cut lengths or coils with an ordered thickness less than 0.230 in. [6.0 mm]; and hot-rolled sheet coils (not cut lengths) with an ordered thickness 0.230 in. [6.0 mm] or greater, intended for use in structural and miscellaneous applications where weight reduction or increased durability is desired [100,120,121].

These steels provide enhanced atmospheric corrosion resistance and are supplied in two types: Type 2 and Type 4, according to [100,120]. As of the 2018 edition, Type 5 was also added to the standard [100,122].

This standard has undergone 14 editions from its initial release in 1985 to the most recent update in 2023. See www.document-center.com (accessed on 7 February 2025) [110] and www.astm.org (accessed on 7 February 2025) [111].

The values of the tensile strength, yield point, and elongation are provided in Table 1, along with the main applications of ASTM A606, as detailed in Table 2.

3.1.4. ASTM A709

The specification ASTM A709 covers carbon and high-strength low-alloy steel structural shapes, plates, and bars, as well as quenched and tempered alloy steel for structural plates intended specifically for use in bridges construction [101,123,124]. Twelve grades are available across five yield strength levels, of which the following grades are designed to provide enhanced atmospheric corrosion resistance: Grades 50W [345W], 50CR [345CR], HPS 50W [HPS 345W], HPS 70W [HPS 485W], and HPS 100W [HPS 690W] [101,124].

The complete document history of this specification includes 31 editions, from its initial release in 2000 to its most recent update in 2024. See www.document-center.com (accessed on 7 February 2025) [110] and www.astm.org (accessed on 7 February 2025) [111].

This standard has undergone several significant revisions over time, with each revision aiming to improve the material specifications, mechanical properties-and testing procedures in line with technological advancements in steel production. The values for tensile strength, yield point, and elongation are provided in Table 1, along with the main structural applications, detailed in Table 2.

Note: For all ASTM standards discussed, the supplementary requirements (e.g., testing methods) can also be found in Table 1.

3.2. Chinese Standard

The GB/T 4171 standard applies to hot-rolled and cold-rolled steel plates, strips, and sections with atmospheric corrosion properties for use in bridges, containers, buildings, towers, and other structures, as shown in Table 2. These structural steels with enhanced corrosion resistance can also be used to manufacture structural components for bolted, riveted, and welded connections [102,125]. The standard defines multiple grades, differentiated by chemical composition and corrosion resistance, as follows: Q355GNH—commonly used for general construction, where moderate corrosion resistance is required; Q415NH—offering enhanced atmospheric corrosion resistance compared to Q355GNH, typically used in more aggressive environmental conditions; and Q235NH—the basic grade of weathering steel, applied in less corrosive environments or specific low-demand applications [125]. The values for tensile strength, yield point, and elongation are presented in Table 1, along with the supplementary requirements (i.e., testing methods).

The GB/T 4171 standard plays a significant role in ensuring that weathering steel remains a viable and reliable option for structural applications in China. By defining strict requirements for chemical composition, mechanical performance, and testing procedures, the standard ensures that weathering steel delivers the expected durability and corrosion resistance in structural use.

Despite certain environmental and aesthetic limitations, weathering steel remains an excellent material choice for exposed infrastructure, due to its natural protective patina, long-term sustainability, and cost-effectiveness. As environmental regulations and maintenance costs increase, the relevance of weathering steel is expected to grow, both in China and worldwide.

In summary, GB/T 4171 is a well-structured standard that supports the ongoing development and deployment of weathering steel across a broad spectrum of structural applications. It addresses the technical performance, environmental adaptability and sustainability demands of the Chinese market.

3.3. European Standard

This document specifies technical delivery conditions for flat and long products of hot-rolled steels with improved atmospheric corrosion resistance, in the grades and qualities defined in the standard. Details such as chemical composition and mechanical properties are provided within the document [103,126].

EN 10025-5 is a critical European standard that ensures the quality and performance of weathering steel used in structural applications. By specifying material grades, mechanical properties, and chemical composition, the standard guarantees that weathering steel delivers the required corrosion resistance and mechanical strength for outdoor applications such as bridges, buildings, and infrastructure projects (see Table 2). The values of tensile strength, yield point, and elongation are listed in Table 1, along with the supplementary requirements (i.e., testing methods). A comparison between weathering steel (EN 10025-5 [103]) and conventional steel (EN 10025-2 [126]) reveals that both exhibit similar mechanical properties.

The corrosion-resistant properties of weathering steel enable it to form a protective oxide layer (patina) that significantly reduces the need for maintenance or recoating, making it a cost-effective and sustainable choice for long-term outdoor applications. This standard is essential for designers, engineers, and manufacturers working with weathering steel to ensure structural integrity, durability, and performance in exposed environments.

EN 10025-5 European Standard includes different grades of weathering steel. In the 2004 version, only two grades were defined: S235 and S355 (see Table 3). However, the 2019 version introduced two additional high-strength grades: S420 and S460, which offer enhanced mechanical properties but are not yet widely included in national guidelines. Despite this, they are commercially available and commonly used in bridge construction. Additionally, the number of sub-grades based on impact toughness increased from two (in 2004) to five (in 2019): J0, J2, K2, J4, and J5.

In versions prior to 2019, EN 10025-5 [103] defined weathering steels whose mechanical characteristics, aside from chemical composition were very similar to those in EN 10025-2 [126]. For this reason, Eurocode 3 (2005 version) treated steels from both parts equally. However, more recent interpretations recognize some key differences, beyond just chemistry, between weathering steels specified in parts 3 [127] and 4 [128] with regard to sub-grade classification. These distinctions are presented in Table 3, which compares the evolution and differentiation of grades across the standards.

3.4. Japanese Standard

JIS G 3125 is a Japanese Industrial Standard (JIS) that specifies the requirements for weathering steel used in structural applications. It defines various grades of weathering steel, commonly referred to as structural steels with enhanced atmospheric corrosion resistance. JIS G 3125 outlines the specifications for hot-rolled steel plates, sheets, and coils intended for structural use, particularly in environments where corrosion resistance is essential due to prolonged exposure to atmospheric conditions. The steel grades covered under JIS G 3125 are designed for use in outdoor applications such as bridges, buildings, signage structures, railway facilities, fences, and even architectural installations [104] (see Table 2).

The standard includes several grades of weathering steel, typically designated with the prefix “SPA” (for “Structural Steel for Atmospheric Corrosion Resistance”). These grades are differentiated based on their mechanical properties and corrosion resistance, each optimized for specific environmental conditions. A commonly used grade is SPA-H: the most widely applied grade of weathering steel in Japan. It offers excellent resistance to atmospheric corrosion and is employed in structural applications subject to a broad range of outdoor conditions. The values for tensile strength, yield point, and elongation are provided in Table 1, as along with the supplementary requirements (i.e., testing methods).

By specifying different grades according to exposure categories, and by providing clear guidelines for fabrication, welding, and testing, JIS G 3125 ensures the durability, structural integrity, and long-term performance of weathering steel in demanding environments. Weathering steel as defined by JIS G 3125, continues to be a preferred material for engineers and architects seeking a sustainable, low-maintenance, and aesthetically appealing solution for exterior and exposed structural projects.

3.5. Indian Standard

IS 2062 is part of the Indian Bureau of Standards (BIS) codes for construction materials. It was originally introduced in 1962 and has since undergone several updates to align with advances in steel production technologies and modern structural requirements [105,129].

IS 2062 specifies the requirements for carbon steel and micro-alloyed steel plates, strips, shapes, and sections (such as angles, tees, beams, channels), as well as flats and bars used in structural applications. It is one of the most extensively used standards in India for carbon steel employed in construction, infrastructure, and industrial projects [105] (see Table 2).

IS 2062 covers multiple steel grades based on mechanical properties and application needs. Notably, it includes: E410: Low tensile strength; E410W: Weathering steel (corrosion-resistant); E450: Higher tensile strength than E410; E510: Medium tensile strength; E550: Higher tensile strength than E450. These grades can be further classified into W and WR categories depending on corrosion resistance and specific environmental performance. The values for tensile strength, yield point, and elongation are detailed in Table 1, as well as the supplementary requirements (i.e., testing methods).

Specifically, the Fe 410 W grade within IS 2062 provides a durable, corrosion-resistant solution for structural applications in aggressive outdoor environments where corrosion resistance is critical. Weathering steel long-term durability, aesthetic appeal, and lower maintenance costs have made it a popular choice in modern construction, particularly for infrastructure projects designed to withstand harsh environmental conditions. However, engineers must consider its higher initial cost and environmental suitability when selecting it for specific applications.

3.6. Australian and New Zealand Standard

AS/NZS 3679.1 is a standard developed by the Australian/New Zealand Standards (AS/NZS) for the specification of structural steel [106,130]. It is widely adopted in the construction, civil engineering, and manufacturing industries across Australia and New Zealand for defining material properties of structural steels used in construction and other structural applications (see Table 2). The standard provides comprehensive technical requirements for the selection, fabrication, and testing of steel materials used in structural applications, with a particular emphasis on high-strength performance and structural reliability. The values for tensile strength, yield point, and elongation, as well as supplementary testing methods are detailed in Table 1.

The standard applies to a wide range of hot-rolled steel sections, including beams, columns, angles, channels, and other standard structural profiles. These materials are primarily used in the construction of buildings, bridges, and other structures requiring high mechanical strength and durability.

AS/NZS 3679.1 defines multiple grades of structural steel, each characterized by specific mechanical properties and applications. The grades are designed to cover a range of applications, from general construction to heavy-duty uses [106,130].

AS/NZS 3679.1:2016 is a key standard that defines the requirements for hot-rolled structural steel used in construction and heavy-duty applications in Australia and New Zealand. Additionally, it is adapted to the unique environmental conditions of Australia and New Zealand, i.e., seismic activity considerations in earthquake-prone regions, and marine atmospheric exposure, which is particularly relevant for coastal or offshore infrastructure [106,131].

Table 1. Findings from the literature review for comparison of different standards on weathering steel.

Standard		Year (First and Last Edition)	Scope	Thickness	Tensile Requirements			Supplementary Requirements
					Tensile Strength (MPa)	Yield Point (MPa)	Elongation (%)	Testing Methods
American Standard	ASTM A242	1979 [109]	Structural steel shapes, plates, and bars	up to 4 in. (101.6 mm)	435–485	290–345	18–21	Product Analysis, Simulated Post-Weld Heat Treatment of Mechanical Test Coupons, Charpy V-Notch Impact Test, Tensile strength, Drop Weight Test, Ultrasonic Examination, Bend Test, and Reduction of Area Measurement [109,112]. Single Heat Bundles [98,113].
		2024 [98]		up to 4 in. (100 mm)
	ASTM A588	1979 [114]	Structural steel shapes, plates, and bars	up to 8 in. (203.2 mm)	435–485	290–345	18–21	Product Analysis, Simulated Post-Weld Heat Treatment of Mechanical Test Coupons, Charpy V-Notch Impact Test, Drop Weight Test, Ultrasonic Examination, Bend Test, Reduction of Area, and Maximum Tensile Strength [114,115]; Charpy V-Notch Impact Test for Structural Shapes: Alternate Core Location [116,117]; Single Heat Bundles [117,118,119].
		2024 [99]		up to 8 in. (200 mm)
	ASTM A606	1985 [120]	Hot and cold-rolled sheet and strip in cut lengths or coils	up to 0.230 in. (6.0 mm)	450–480	310–340	22	Tension Test, Hardness Test, Charpy V-Notch Impact Test, Bending Properties [100,122,132].
		2023 [100]
	ASTM A709	2000 [123]	Structural shapes, plates, and bars, quenched and tempered alloy steel	up to 4 in. (100 mm)	485–895	345–690	18–21	Tension Test, Charpy V-Notch Impact Test, Brinell hardness test, Non-Fracture-Critical, T, Material; Toughness Tests and Marking, Fracture-Critical, F, Material; Toughness Testing and Marking, Ultrasonic Examination [124,133,134,135].
		2024 [101]
Chinese Standard	GB/T	1984 [125]	Hot-rolled and cold rolled steel plates, strips, and sections	up to 12 in. (300 mm)	215–680	345–510	22–24	Chemical Composition Analysis, Tensile Strength Test, Impact Toughness, Corrosion Resistance Test, Bend Test [102,125,136].
	4171	2008 [102]
European Standard	EN	2004 [137]	Flat and long products of hot rolled steels	up to 12 in. (300 mm)	350–680	195–355	14–26	Ultrasonic testing, Ultrasonic testing of H beams with parallel flanges and IPE beams, Non-destructive testing–Ultrasonic testing of steel bars, Micrographic determination of the apparent grain size [103,137].
	10025-5	2019 [103]
Japanese Standard	JIS	1987 [138]	Hot-rolled steel plates, sheets, and coils	up to 4 in. (100 mm)	480–490	335–355	15–22	Tensile testing, Impact testing, Corrosion testing [104,138,139,140].
	G-3125	2021 [104]
Indian Standard	IS	1962 [129]	Hot-rolled medium and high tensile structural steel	up to 4 in. (100 mm)	540–650	380–550	12–20	Tensile Tests, Bend Test, Impact Tests, Chemical Analysis, Ultrasonic Testing, Y Groove crackability test [105,129].
	2062	2011 [105]
Australian Standard	AS/NZS	1996 [130]	Hot-rolled structural steel bars and sections.	up to 12 in. (300 mm)	400–750	250–450	18–22	Tensile test, Impact test, Charpy V-Notch Impact Test, Ultrasonic testing, Bend Tests [106,130,131].
	4600	2016 [106]

Table 1. Findings from the literature review for comparison of different standards on weathering steel.

Standard		Year (First and Last Edition)	Scope	Thickness	Tensile Requirements			Supplementary Requirements
					Tensile Strength (MPa)	Yield Point (MPa)	Elongation (%)	Testing Methods
American Standard	ASTM A242	1979 [109]	Structural steel shapes, plates, and bars	up to 4 in. (101.6 mm)	435–485	290–345	18–21	Product Analysis, Simulated Post-Weld Heat Treatment of Mechanical Test Coupons, Charpy V-Notch Impact Test, Tensile strength, Drop Weight Test, Ultrasonic Examination, Bend Test, and Reduction of Area Measurement [109,112]. Single Heat Bundles [98,113].
		2024 [98]		up to 4 in. (100 mm)
	ASTM A588	1979 [114]	Structural steel shapes, plates, and bars	up to 8 in. (203.2 mm)	435–485	290–345	18–21	Product Analysis, Simulated Post-Weld Heat Treatment of Mechanical Test Coupons, Charpy V-Notch Impact Test, Drop Weight Test, Ultrasonic Examination, Bend Test, Reduction of Area, and Maximum Tensile Strength [114,115]; Charpy V-Notch Impact Test for Structural Shapes: Alternate Core Location [116,117]; Single Heat Bundles [117,118,119].
		2024 [99]		up to 8 in. (200 mm)
	ASTM A606	1985 [120]	Hot and cold-rolled sheet and strip in cut lengths or coils	up to 0.230 in. (6.0 mm)	450–480	310–340	22	Tension Test, Hardness Test, Charpy V-Notch Impact Test, Bending Properties [100,122,132].
		2023 [100]
	ASTM A709	2000 [123]	Structural shapes, plates, and bars, quenched and tempered alloy steel	up to 4 in. (100 mm)	485–895	345–690	18–21	Tension Test, Charpy V-Notch Impact Test, Brinell hardness test, Non-Fracture-Critical, T, Material; Toughness Tests and Marking, Fracture-Critical, F, Material; Toughness Testing and Marking, Ultrasonic Examination [124,133,134,135].
		2024 [101]
Chinese Standard	GB/T	1984 [125]	Hot-rolled and cold rolled steel plates, strips, and sections	up to 12 in. (300 mm)	215–680	345–510	22–24	Chemical Composition Analysis, Tensile Strength Test, Impact Toughness, Corrosion Resistance Test, Bend Test [102,125,136].
	4171	2008 [102]
European Standard	EN	2004 [137]	Flat and long products of hot rolled steels	up to 12 in. (300 mm)	350–680	195–355	14–26	Ultrasonic testing, Ultrasonic testing of H beams with parallel flanges and IPE beams, Non-destructive testing–Ultrasonic testing of steel bars, Micrographic determination of the apparent grain size [103,137].
	10025-5	2019 [103]
Japanese Standard	JIS	1987 [138]	Hot-rolled steel plates, sheets, and coils	up to 4 in. (100 mm)	480–490	335–355	15–22	Tensile testing, Impact testing, Corrosion testing [104,138,139,140].
	G-3125	2021 [104]
Indian Standard	IS	1962 [129]	Hot-rolled medium and high tensile structural steel	up to 4 in. (100 mm)	540–650	380–550	12–20	Tensile Tests, Bend Test, Impact Tests, Chemical Analysis, Ultrasonic Testing, Y Groove crackability test [105,129].
	2062	2011 [105]
Australian Standard	AS/NZS	1996 [130]	Hot-rolled structural steel bars and sections.	up to 12 in. (300 mm)	400–750	250–450	18–22	Tensile test, Impact test, Charpy V-Notch Impact Test, Ultrasonic testing, Bend Tests [106,130,131].
	4600	2016 [106]

Table 2. Findings from the literature review for comparison of different standards on weathering steel (Applications).

Standard		Key Features	Application
			Structural	Non-Structural
American Standard ASTM	ASTM	For use as structural members	Bridges, Buildings [98]	Railway Coal Cars [109]
	A242	First standard for weathering steel, focused on corrosion resistance and strength [98,109]
	ASTM	For use in welded bridges and buildings	Bridges, Buildings [116,119]	Railway [114,115]
	A588	Introduced high-strength low-alloy structural steel. Improved guidelines for welding procedures, as weathering steel can be challenging to weld due to its higher copper content [114,115,116,117,118,119]
	ASTM	For use in structural and miscellaneous purposes	Bridge, Buildings, Infrastructure [100,120,121,122,132,141]	Facades, Roofing, and Exterior Cladding [100,120,121,122,132,141]
	A606	Architectural applications [100,120,121,122,132,141]
	ASTM	Standard for carbon steel and high-strength low-alloy structural steel used in bridges [101,123,124,133,134,135]	Bridges [101,123,124,133,134,135]	-
	A709
Chinese Standard	GB/T	Provides excellent atmospheric corrosion resistance for long-term use [102,125,136]	Bridges, Buildings, Tower Pier [102,125,136]	Fencing and Barriers, Signage, Container [102,125,136]
	4171
European Standard	EN	Updated European standard, aligning with international specifications for weathering steel [103,137]	Bridges, Buildings [103,137]	Sculptures, Facades [103,137]
	10025-5
Japanese Standard	JIS	High resistance to atmospheric corrosion, typically used in harsher environmental conditions [104,138]	Bridges, Buildings [104,138,139,140]	Sculptures, railway carriage, containers production [104,138,139,140]
	G3125
Indian Standard	IS	Corrosion-resistant steel used for moderate environmental exposure [105,129]	Bridges, Buildings [105,129]	Machinery, Railway [105,129]
	2062
Australian Standard	AS/NZS	Weather-resistant steel for structural and civil engineering applications [106,130,131]	Bridges, Buildings, Heavy Equipment [106,130,131]	Industrial Structures, Components in machinery [106,130,131]
	4600

Table 2. Findings from the literature review for comparison of different standards on weathering steel (Applications).

Standard		Key Features	Application
			Structural	Non-Structural
American Standard ASTM	ASTM	For use as structural members	Bridges, Buildings [98]	Railway Coal Cars [109]
	A242	First standard for weathering steel, focused on corrosion resistance and strength [98,109]
	ASTM	For use in welded bridges and buildings	Bridges, Buildings [116,119]	Railway [114,115]
	A588	Introduced high-strength low-alloy structural steel. Improved guidelines for welding procedures, as weathering steel can be challenging to weld due to its higher copper content [114,115,116,117,118,119]
	ASTM	For use in structural and miscellaneous purposes	Bridge, Buildings, Infrastructure [100,120,121,122,132,141]	Facades, Roofing, and Exterior Cladding [100,120,121,122,132,141]
	A606	Architectural applications [100,120,121,122,132,141]
	ASTM	Standard for carbon steel and high-strength low-alloy structural steel used in bridges [101,123,124,133,134,135]	Bridges [101,123,124,133,134,135]	-
	A709
Chinese Standard	GB/T	Provides excellent atmospheric corrosion resistance for long-term use [102,125,136]	Bridges, Buildings, Tower Pier [102,125,136]	Fencing and Barriers, Signage, Container [102,125,136]
	4171
European Standard	EN	Updated European standard, aligning with international specifications for weathering steel [103,137]	Bridges, Buildings [103,137]	Sculptures, Facades [103,137]
	10025-5
Japanese Standard	JIS	High resistance to atmospheric corrosion, typically used in harsher environmental conditions [104,138]	Bridges, Buildings [104,138,139,140]	Sculptures, railway carriage, containers production [104,138,139,140]
	G3125
Indian Standard	IS	Corrosion-resistant steel used for moderate environmental exposure [105,129]	Bridges, Buildings [105,129]	Machinery, Railway [105,129]
	2062
Australian Standard	AS/NZS	Weather-resistant steel for structural and civil engineering applications [106,130,131]	Bridges, Buildings, Heavy Equipment [106,130,131]	Industrial Structures, Components in machinery [106,130,131]
	4600

Table 3. Product forms for the different steel grades with improved atmospheric corrosion resistance depending on their thickness (EN 10025-5: 2004 and 2009 version).

Designation			Flat Products		Long Products
					Section Shapes		Bars	Rods
			Nominal Thickness		Nominal Thickness or Diameter
Steel Name		Steel Number	mm		mm
			≤12	≤150	≤40	≤63	≤150	≤60
EN 10025-5: 2004	S235J0W	1.8958		x	x	x	x	x
	S235J2W	1.8961		x	x	x	x	x
	S355J0WP	1.8945	x		x
	S355J2WP	1.8946	x		x
	S355J0W	1.8959		x	x	x	x	x
	S355J2W	1.8965		x	x	x	x	x
	S355K2W	1.8967		x	x	x	x	x
EN 10025-5: 2019	S355J4W	1.8787		x		x	x	x
	S355J5W	1.8991		x
	S420J0W	1.8943		x		x
	S420J2W	1.8949		x		x
	S420K2W	1.8997		x		x
	S420J4W	1.8954		x
	S420J5W	1.8992		x
	S460J0W	1.8966		x		x
	S460J2W	1.8980		x		x
	S460K2W	1.8990		x		x
	S460J4W	1.8981		x
	S460J5W	1.8993		x

Table 3. Product forms for the different steel grades with improved atmospheric corrosion resistance depending on their thickness (EN 10025-5: 2004 and 2009 version).

Designation			Flat Products		Long Products
					Section Shapes		Bars	Rods
			Nominal Thickness		Nominal Thickness or Diameter
Steel Name		Steel Number	mm		mm
			≤12	≤150	≤40	≤63	≤150	≤60
EN 10025-5: 2004	S235J0W	1.8958		x	x	x	x	x
	S235J2W	1.8961		x	x	x	x	x
	S355J0WP	1.8945	x		x
	S355J2WP	1.8946	x		x
	S355J0W	1.8959		x	x	x	x	x
	S355J2W	1.8965		x	x	x	x	x
	S355K2W	1.8967		x	x	x	x	x
EN 10025-5: 2019	S355J4W	1.8787		x		x	x	x
	S355J5W	1.8991		x
	S420J0W	1.8943		x		x
	S420J2W	1.8949		x		x
	S420K2W	1.8997		x		x
	S420J4W	1.8954		x
	S420J5W	1.8992		x
	S460J0W	1.8966		x		x
	S460J2W	1.8980		x		x
	S460K2W	1.8990		x		x
	S460J4W	1.8981		x
	S460J5W	1.8993		x

To facilitate a clearer understanding of the key content covered by the weathering steel standards discussed in Section 3, and in reference to Table 1, Figure 3 illustrates the scope of application of each standard with respect to the various steel product forms and structural elements used in construction, manufacturing, and fabrication. This includes plates, sheets, bars, shapes, coils, and other hot-rolled or cold-formed components.

Furthermore, Figure 4 complements this by displaying the typical structural and infrastructure applications associated with each standard—such as bridges, buildings, railway structures, containers, and architectural elements. These applications are also cross-referenced and detailed in Table 2, offering an integrated view of standard-specific usage scenarios across different sectors.

4. Weathering Steel Applications

The origin of weathering steel can be traced back to a solution developed in 1933 by the United States Steel Corporation (1933), initially intended for use in railway coal cars [1,2,3]. The adoption of weathering steel in civil engineering and architecture applications remained limited until the 1960s, when interest in its durability and aesthetic qualities expanded. Flat products such as sheets and bars aroused interest in various application fields, both for metal constructions and for building facades, and in a few years, weathering steel was consolidated as a construction material for several hundred bridges [9,142]. In the research from Gammon [21], a 16-ton mineral wagon vehicle is illustrated with other important types of vehicles. The underframes of this vehicle was made of weathering steel, as well as the sides, ends, body, floor, roof, and end doors. This vehicle is shown in Figure 5 and corresponds to the 30s.

The following are applications in both civil engineering and architecture, considering both structural and non-structural perspectives

4.1. Civil Engineering Applications

4.1.1. Structural Applications

A notable example is the application of weathering steel in bridge construction, which significantly contributed to the material’s growing popularity. The first such bridge was built over the New Jersey turnpike in 1964 [143]; see Figure 6.

In Italy, the first significant applications of weathering steel in the road sector began in the 1980s, gradually gaining considerable acceptance among engineers, public authorities, and construction companies [144].

Most Italian designs feature composite steel-concrete section with unpainted weathering steel beams.

Figure 7 shows some of the earliest Italian applications of weathering steel in the road sector.

The decision to use weathering steel for the Hunslet Viaduct was supported by the client, who welcomed the idea of evoking the industrial heritage of Hunslet, an area historically known as Leeds’ workshop.

Figure 8 shows the Hunslet Viaduct under construction.

4.1.2. Non-Structural Applications

Chris Brammall was commissioned by Sunderland City Council to design and construct a bridge connecting two footpaths across the lake of the Barnes Park. The supporting structure is made of weathering steel, which also functions as safety barrier for pedestrians, while the footbridge deck composed of reinforced concrete(see Figure 9).

The Stadion Letzigrund’s weathering steel fencing appears as a textured weathering steel skin that wraps around the stadium, with shades ranging from rusty brown to burnt orange, creating an aesthetic effect that changes with the light and weather, lending dynamism and character to the work. See Figure 10.

The pedestrian walkway over the Arga River, connecting the San Jorge and San Juan neighborhoods of Pamplona, is a 110-m-long timber footbridge that stands out for its sculptural character, defined by its distinctive materials and curved cladding made of weathering steel. See Figure 11.

4.2. Architectural and Sculpture Applications

At the same time, architects began using weathering steel in building construction and monuments restoration. One of the first significant applications was the John Deere headquarters (Figure 12) which used weathering steel for the building´s exterior structure. Completed in 1964 in Moline, Illinois, it was designed by the renowned architect Eero Saarinen and marked the first use of weathering steel outside industrial applications in the United States [6].

Another example is the Museum-Laboratory of the Zampogna in Villa Latina, Italy (Figure 13), which can be found at Fondazione Promozione Acciaio [149].

The WU Campus of the Vienna University of Economics and Business (WU), designed by the Austrian studio BUSarchitektur in collaboration with BOAnet for landscape planning, is a landmark work of contemporary architecture. This campus is distinguished by its focus on sustainability and urban integration, featuring weathering steel façade. See Figure 14.

Restorations projects and sculptures are also fields where weathering steel has been, and continues to be, widely used [151,152]. Several renowned artists worldwide incorporate weathering steel in their sculptures, such as Richard Serra, an American artist who has made weathering steel one of his signature materials. His monumental and minimalist works have earned him international recognition, including The Matter of Time [153], Guggenheim Museum in Bilbao, Spain (1994–2005) (Figure 15).

Formes femelles, created in France in 1969 (Figure 16), is another example of sculpture made entirely of weathering steel [7]. In this context, the use of weathering steel for outdoor sculptures began to emerge in the 1960s.

The sculpture titled “Evolution of Life” is a monumental work located in Plaza del Progreso, Arganda del Rey, Community of Madrid, Spain. Conceived by sculptor Fernando Capa in collaboration with architect Juan Antonio Chamorro, it was installed in 2003. See Figure 17.

Since its inception in the 1930s, weathering steel has evolved from a practical material used in transportation and industry into a symbol of modern architectural and artistic expression. Its unique combination of aesthetics, durability, and corrosion resistance has made it a preferred choice among architects, engineers, and artists alike. The material’s versatility continues to inspire innovative designs, from bridges and sculptures to sustainable urban landscapes, and its use shows no signs of slowing down in the years ahead.

5. Engineering Design Considerations

5.1. General Considerations from ECCS

Regarding design considerations, effective guidance is provided by the European guidelines ECCS, which address design, detailing, construction, in service inspection, and maintenance for bridges [9]. Over the last three decades, weathering steel has played a predominant role in the constructions of metal bridges due to its minimal maintenance requirements, whereas few applications are available for buildings. In this perspective, satisfactory performance of structural and non-structural weathering steel constructions is addressed in the ECCS, also complemented by good practice in structural detailing. To achieve optimal weathering steel construction performance, several structural detailing aspects must be considered-whether in architectural applications such as facades or even sculptures or civil engineering constructions such as bridges. For instance, expansion joints and drainage must be detailed to ensure all parts of the steelwork can dry out properly. ECCS stresses that moisture and debris retention should be avoided, and adequate ventilation must be ensured [9]. During the initial years, run-off from the steelwork, as the protective ‘patina’ develops, contains corrosion products that may stain substructures and paving slabs. This risk is highest in the early months when the corrosion rate is greatest, but it decreases over time as fewer corrosion products are released, thereby reducing rust staining. Avoiding all types of contamination to the structure or its surrounding elements is critical [155]. In box girders (common in bridges), it is essential to prevent moisture accumulation by allowing the structure to “breathe” ensuring airflow to dry damp surfaces. Internal diaphragms and stiffeners should be detailed to facilitate instant drainage of any collected water at the lowest point [156].

Interfaces between steel and concrete must be sealed with an appropriate sealant to prevent moisture ingress. Connections to galvanically dissimilar metals (e.g., zinc-plated bolts) should be avoided to prevent accelerated local corrosion [155]. During early rust patina formation, corrosion products may rub off onto clothing if the public contacts the surface, and prolonged contact has sometimes led to surface polishing of weathering steel. In addition, connections to more or less noble metals risk corrosion of either the weathering steel or the less noble component [157]. Welded connections are particularly important: all joints should be continuously welded on all sides to prevent moisture ingress and corrosion within the crevices formed by contact surfaces [43]. It is recommended to use preloaded bolts, even for non-structural connections to ensure tight contact and avoid crevice corrosion. Bolting assemblies should have corrosion resistance properties to those of the steel plates and sections [158].

A study conducted in [159] confirmed that inadequate control from bridge joints is the major cause of deterioration in steel and concrete bridge components exposed to roadway deicing chemicals. Finally, corrosion causes only a slight decrease in the fatigue strength of plain weathering steel section or sheets, and no reduction is required for welded or bolted joints, which are usually the critical points for fatigue design. Fatigue failures in bridges almost always initiate at geometric discontinuities or stress concentrations, such as welded or bolted connections, which have a much greater impact on fatigue strength than corrosion pits in weathering steel [160].

5.2. Inspection, Monitoring, and Maintenance in Weathering Steel Bridges

Weathering steel has been used in highway bridges since 1964, and its popularity has increased in recent decades due to its various benefits, including economic and environmental advantages. This material is being applied in different types of infrastructure, particularly in bridges made of composite structures, i.e., steel and reinforced concrete [161,162]. Studies have shown that using weathering steel reduces both initial and life-cycle costs [163,164]. Current highway legislation in the United States mandates the consideration of life-cycle cost analysis in the selection process of highway materials [159].

Weathering steel bridges still require routine inspections, monitoring, and occasional maintenance to ensure satisfactory performance. Hence, it is important to identify any specific problems to which such bridges may occasionally be prone as early as possible, in order to implement appropriate remedial measures [9].

5.2.1. Bridge Inspections

Visual inspections of weathering steel bridges should be carried out by suitably experienced inspectors at least every two years. The surface condition of the ‘patina’ is a good indicator of performance [165]. An adherent, fine-grained rust patina indicates that corrosion is progressing at an acceptable rate, whereas coarse, laminated rust layers and flaking suggest unacceptable performance. Other signs to look for and areas to investigate during visual inspection include leaking expansion joints, accumulation of dirt or debris, moisture retention due to overgrown vegetation, faulty drainage systems, condition of sealants at concrete/steel interfaces, and excessive corrosion products at bolted joints [158].

If any serious problems are identified during the visual inspection, the underlying cause should be investigated and the issue rectified as soon as possible.

5.2.2. Monitoring of Steel Thickness

The corrosion rate of weathering steel bridges should be monitored every six years by measuring the remaining steel thickness at clearly identified critical points on the structure [67,68]. These points should be defined on the as-built drawings or in the bridge maintenance manual, along with original (reference) thickness measurements taken at the end of the construction period. If, after a period of approximately 18 years, the predicted section loss over the design life of the structure exceeds the original allowance, then remedial measures may need to be implemented. The 18-year period is suggested because the corrosion rate is initially higher during the formation of the patina, before stabilizing to a more characteristic, lower rate.

On-site monitoring is essential to ensure the ultra-long service life of weathering steel structures [55].

5.2.3. Routine Maintenance

Surfaces contaminated with dirt or debris should be periodically cleaned using low-pressure water washing, taking care not to disrupt the protective ‘patina’ [166]. The cleaning should also be carried out annually, at the end of the de-icing season, if it is found in practice that chlorides are adversely affecting the stability of the rust ‘patina’ and causing corrosion of the substrate.

Overhanging vegetation that causes persistent dampness should be removed, and drainage systems should be regularly cleared. Any leaks should be traced to their source, and the drainage systems or joints responsible should be repaired or replaced. Finally, if there is evidence of crevice ‘pack-out’ at bolted joints, the joint edges should be sealed with an appropriate sealant [67,68].

Lifecycle Cost Analysis (LCCA) of weathering steel bridges consistently demonstrates their economic advantage over conventional steel and concrete structures. Due to the inherent corrosion resistance of weathering steel, these bridges require significantly less maintenance—particularly by eliminating repainting cycles—which results in lower long-term costs. According to the Federal Highway Administration [167], weathering steel bridges can achieve a 10–30% reduction in total lifecycle costs over a 75-year period, primarily due to reduced maintenance requirements and fewer user disruptions. Investigations from [168] found that these structures not only minimize direct maintenance expenditures but also reduce indirect costs associated with traffic delays and environmental impacts. Additionally, studies in [169] confirmed that in suitable atmospheric conditions, particularly rural and low-chloride environments, weathering steel offers a service life exceeding 75 years, with corrosion rates as low as 0.01 mm/year. These factors collectively position weathering steel as a cost-effective and sustainable material choice for long-span bridge infrastructure.

6. Pros and Cons of Weathering Steel

6.1. Limitations of Using Weathering Steel

Despite the good mechanical performance of weathering steel, initial construction costs are a primary consideration during the designing phases. However, the reduced costs associated with lower maintenance requirements throughout the service life of the structure often compensate for the higher initial investment, making weathering steel a cost-effective solution in the long term [9].

The ideal environments for weathering steel applications are rural and urban areas where the steel is exposed to alternating wet and dry cycles from clean rainfall. This promotes the formation of a dense, tightly adhering, and stable oxide layer that provides effective corrosion protection [9,15,92]. Conversely, environments with high concentrations of strong chemical or industrial pollutants—particularly marine environments—should be avoided [5,74].

Due to the specific characteristics of weathering steel, some aspects require careful consideration. One of the most important is the suitability of the construction site. To accurately assess whether weathering steel is appropriate for a given location, it is necessary to classify the atmospheric corrosivity using one of two methods described in BS EN ISO 9223 [170]. In method I, environmental data approach combines measurements of three key environmental factors (a. time of wetness; b. atmospheric sulfur dioxide pollution P0–P3; and c. airborne salinity S0–S3) in accordance with BS EN ISO 9225 [171] to determine the overall corrosivity category (C1–C5) of the environment. In method II, the corrosion rate is measured according to EN ISO 9226 [172]. Unfortunately, both methods require data collection over a full year to obtain representative average values. Therefore, EN ISO 12944-2 [173] provides a useful alternative: it correlates corrosivity classifications (C1 to CX) with descriptions of typical environments. This guidance, illustrated in

Table 4. Corrosion categories for typical environments, EN ISO 12944-2 [173].

Corrosion Categories for Typical Environments
Corrosion Category		Typical Environment
C1	very low	N/A—Interior environments only
C2	low	Atmospheres with low levels of pollution: mostly rural areas
C3	medium	Urban and industrial atmospheres, moderate sulfur dioxide pollution; coastal area with low salinity
C4	high	Industrial areas and coastal areas with moderate salinity
C5	very high	Industrial areas with high humidity and aggressive atmospheres and coastal areas with high salinity
CX	extreme	Offshore areas with high salinity and industrial areas with extreme humidity and aggressive atmosphere and sub-tropical and tropical atmospheres

, is particularly helpful as a starting point when actual measurements are unavailable, and in many cases, further data collection is unnecessary.

According to the Standards for Highways CD 361—Weathering Steel for Highway Structures [174], corrosion allowances have been defined for different environmental categories. For a lifespan of 120 years with both faces of the material exposed, the following allowances apply: C2: 1 mm; C3: 2 mm; C4: 3 mm.

So, based on this information, an additional 1 mm of thickness should be sufficient to account for corrosion loss over a 40-year period in C2 to C4 environments. In C5 environments, exposure to high concentrations of chloride ions from seawater can severely impact the protective oxide layer by maintaining a continuously damp surface on the metal. As a result, weathering steel in such condition continues to corrode at a rate similar to that of conventional carbon steels [174].

Accordingly,

Table 5. Allowances for the loss of thickness for a design life of 100 years [9].

Country (Guideline)	Allowances for the Loss of Thickness Related to Corrosion Classification in EN ISO 9223 (VI)
	C1	C2	C3	C4	C5
Belgium [175]	-	0.11–0.8	0.53–1.2	1.05–1.5	not allowed
Germany [156]	-	0.8	1.2	1.5	not allowed
United Kingdom [174] (for 120 years)	0	0.5	1.0	1.5	not allowed
France [165]	not applicable	1.0	1.0	1.0	not allowed
Spain [176] (exterior elements)	1.0	1.0	1.0	not allowed	not allowed
ECCS recommendation for bridges [9]	not applicable	0.8	1.0	1.5	not allowed

, also from the ECCS European design guide [9] for the use of weathering steel in bridge construction, provides an overview of the recommended thickness allowances per exposed surface for a 100-year design life, including practical recommendations for design and material selection.

6.2. Benefits of Using Weathering Steel

Weathering steel bridges offer numerous advantages and have demonstrated a solid performance track record. Conventional steel, benefiting from the latest advances in automated fabrication and construction techniques, already provides economic solutions that meet the demands of safety, rapid construction, attractive appearance, minimal maintenance, and future adaptability. Weathering steel bridges share all these qualities while offering additional benefits. A study by [177] indicated that weathering steel bridges built over the last 20 years are generally performing well.

The use of weathering steel provides several advantages, especially in terms of construction time and costs, primarily by eliminating the need for painting. This translates into very low maintenance [9,48] over the structure’s life cycle, particularly for bridges. Bridges composed of composite structures (steel and concrete) require only a periodic inspection and cleaning to ensure continued satisfactory performance [48,52]. Although weathering steel is slightly more expensive than conventional steel, the savings from the elimination of a paint system usually offset the higher material cost [52]. For instance, the initial cost of a weathering steel bridge is comparable to that of a conventional steel bridge, as demonstrated in a study of eight bridges in the UK [142]. The minimal future maintenance requirements of weathering steel bridges greatly reduce both direct maintenance costs and indirect costs, such as traffic delays or rail service interruptions. These savings often far exceed the modest 5% premium on initial capital costs [59,142]. Overall construction durations are shortened because shop and site painting operations are eliminated [9,48]. Environmental and health benefits also result from not applying paint, helping protect both workers and the surrounding ecosystem—thus enhancing the sustainability of weathering steel [9,48,59]. The attractive appearance of weathering steel bridges and, in general, in structures and non-structural buildings often blends harmoniously with natural and urban environments. This visual appeal improves over time with the development of a stable oxide layer, which typically darkens to a rich brown color [67]. Finally, long-term performance is another critical advantage worth noting [67,177].

7. Innovative Developments and Future Trends

Future research on weathering steel will focus on the development of new optimized alloys suitable for more aggressive environments, such as coastal or industrial regions with high concentrations of chlorides and sulfur dioxide. Recent studies propose incorporating elements such as nickel (Ni), cobalt (Co), and rare earth elements to enhance the stability of the protective patina [81,89,178]. At the same time, advances are being made in AI-based predictive models and digital twin systems to monitor atmospheric corrosion behavior in real time [179,180]. These models will enable predictive lifecycle management and support more precise maintenance decision-making. Additionally, the use of embedded sensors and advanced electrochemical techniques—such as electrochemical impedance spectroscopy (EIS) and X-ray photoelectron spectroscopy (XPS)—is expected to increase for high-resolution monitoring of structural deterioration [181]. Finally, a closer integration is anticipated between material selection and sustainable design principles, promoting standards that support the use of recyclable weathering steel in infrastructure with low environmental impact [182].

8. Conclusions

This paper presented an extensive review of the use of weathering steel in civil engineering and architecture. Its main focus was on the development of scientific and the technical knowledge in the field, highlighting the material’s potential, the current state of research, and future directions emerging from recent advances. In this context, the paper also serves as a reference for expert researchers, newcomers to the field, and practitioners alike, facilitating a deeper cross-fertilization of ideas.

Starting with a comprehensive bibliometric analysis, the paper examined the temporal evolution of weathering steel applications in the construction sector. This analysis revealed that much of the research conducted over the years has concentrated on the chemical composition of the steel, particularly the formation of a stable and protective patina. This aspect plays a central role in weathering steel applications due to its significant enhancement of corrosion resistance and the resulting long-term reduction in maintenance needs compared to conventional steel.

The review confirmed that weathering steel is widely used in structural applications, especially in bridges, where maintenance and corrosion concerns are critical. However, real-world applications in buildings—both structural and non-structural—are also increasing worldwide, thanks to the material’s aesthetic appeal, durability, and potential to support life-cycle efficiency and environmental sustainability.

Despite numerous studies highlighting the material’s chemical and mechanical potential, the technical literature revealed a general lack of detailed and specialized design guidelines that address the specific characteristics of weathering steel in both structural and non-structural components. In fact, our analysis of current standards showed that, with exception of the United States, where codes for bridges (primarily) and buildings are more developed, there is a global need for improved and widely accepted codified design standards.

On a positive note, emerging research trends are promising. They focus on optimizing alloys for more aggressive environments and on maximizing the material’s contribution to life-cycle efficiency. These advances reinforce the role of weathering steel as a key material in the future development of both structures and infrastructure.