I. Background of Anti-corrosion for Building Steel Structures

Municipal public facilities, such as large exhibition centers, sports venues, airport terminals, TV towers, and bridges, all use a large amount of steel as the primary structural form. Steel is an important structural material in modern buildings. It has high strength, stable performance, good toughness, convenient processing, suitability for mass production, easy quality control, and quick installation. Therefore, it is particularly suitable for constructing large-span, super-high, and heavy buildings.

In typical urban environments, factors like car exhaust emissions, sulfur-containing gases from power plants and boiler chimneys, industrial air pollution in industrial cities, and salt mist erosion in coastal cities, as well as humid heat in southern cities, inevitably lead to corrosion of steel structures. The use of anti-corrosion coatings to protect steel structures in municipal public facilities is an economically feasible method, and a suitable coating system can achieve durability of more than 25 years.

Apart from considering corrosion protection, another key coating to consider is fire protection, as the fire resistance of building steel structures is relatively poor. This manifests in two aspects: first, the high thermal conductivity of steel leads to quick temperature rise during a fire; second, the strength of steel decreases rapidly as the temperature increases, causing the steel structure to collapse under external loads. The main goal of fire protection for building steel structures is to ensure enough escape time during a fire. Therefore, to prevent and reduce the fire hazards of building steel structures, scientific fire protection design and reliable, economical fire protection measures must be adopted.

In the application of anti-corrosion and fireproof coatings for steel structures in municipal public facilities, long-term durability, aesthetic decoration, and environmental protection must all be taken into account. Heavy-duty anti-corrosion and fireproof coatings used for building steel structures should reflect the best combination of performance, aesthetics, and environmental regulations.

II. Corrosive Media in Building Steel Structures

The corrosive media that building steel structures face mainly include:

1. Moisture in the Atmosphere

In urban environments, the air humidity is relatively high, especially in cities near rivers, lakes, or the sea. The moisture in the air forms a water film on the steel structure's surface, accelerating the corrosion process.

2. Oxygen in the Atmosphere

Oxygen is a key factor in causing steel oxidation reactions. It combines with moisture on the steel surface to form corrosive electrolytes.

3. Air Pollution

In cities, industrial emissions, car exhausts, and pollutants contain sulfur dioxide (SO2), nitrogen oxides (NOx), and other acidic gases, which dissolve and exacerbate the corrosion of steel structures.

4. Dust and Particles

Dust and particles in cities can adhere to the steel structure's surface. These substances may contain corrosive components, accelerating the corrosion process.

5. Salt

Steel structures in coastal cities are also affected by salt mist. Salt in seawater (mainly sodium chloride NaCl) is highly corrosive and can accelerate the corrosion rate of metal.

6. Microorganisms

In humid environments, microorganisms such as bacteria and fungi may also participate in the corrosion process, especially in warm and humid climates.

7. Chemicals

Certain chemicals in urban areas, such as detergents and antifreeze, may come into contact with steel structures. The components of these chemicals can promote corrosion.

8. Temperature Changes

Temperature differences in cities also affect steel structures. Particularly with large temperature variations between day and night, temperature changes lead to condensation on the surface of the steel structure, accelerating corrosion.

9. Industrial Emissions

Steel structures in industrial areas are also affected by specific industrial emissions such as acidic gases and heavy metal ions.

To address the impact of these corrosive media, urban steel structures typically require effective anti-corrosion measures, such as high-performance coatings, cathodic protection systems, and the use of corrosion-resistant alloys to ensure the structure's durability and safety.

I. Cited Standards

Relevant national standards, mandatory standard clauses, etc.;

"Construction Corrosion Protection Engineering Construction and Acceptance Specification" (GB50212-2002)

"Standard for Corrosion and Rust Removal Levels of Steel Surface Before Coating" (GB8923-1988)

"Safety Regulations for Coating Operations and Safety Management Rules" (GB6514-1995)

"Quality Requirements for Anti-corrosion Coatings" (GB6514-1991)

"Safety Regulations for Coating Operations, Painting Process Safety, and Ventilation and Purification" (DJ/T6931-1999)

"Industrial Equipment and Pipeline Corrosion Protection Engineering Construction and Acceptance Specification" (HGJ229-91)

"Safety Regulations for Coating Operations, Surface Treatment Process Safety" (GB7692-87)

"Noise Limits for Construction Site Boundaries" (GB12523-90)

ISO9001 Quality Management System Documents

ISO14001 Environmental Management System Documents

GB/T28001 Occupational Health and Safety Management System Documents

I. Design Basis

The corrosion protection coating specifications for steel structures are primarily based on ISO 12944. ISO 12944 is currently the globally recognized authoritative standard, compiled by the International Organization for Standardization for owners, designers, consulting advisors, coating contractors, and coating manufacturers involved in corrosion protection work. It provides essential references for these individuals, organizations, and entities.

ISO 12944 comprehensively introduces all the requirements for steel structure protective coatings, including design life, corrosive environments, structural design, surface treatment, coating systems, coating product performance, construction supervision, and the development of new construction and maintenance solutions. When designing a steel structure corrosion protection coating system, ISO 12944 outlines the main considerations as follows.

Analyzing the corrosive environment of the steel structure to determine its corrosion level (ISO 12944-2);

Determining the desired protection lifespan for the steel structure (ISO 12944-5);

Determining the operational conditions of the steel structure, such as temperature, humidity, media, indoor, and outdoor environments;

Understanding the relevant national standards for building steel structure corrosion coatings;

Selecting the most cost-effective coating types and film thicknesses, and determining the appropriate coating system.

1. About Corrosive Environments

The corrosive environment defined in ISO 12944-2 serves as the guide for developing protective coatings. Most steel structures in public facilities, such as stadiums and exhibition centers, are typically situated in environments ranging from C2 to C4. Steel structures in metallurgical and petrochemical enterprises, as well as marine engineering, are generally in highly corrosive C5 environments. The corrosive environments and conditions listed in ISO 12944-2 (see Table 3-3-93) do not cover all situations. Therefore, designers need to tailor their coating solutions based on their own research and experience.

Environmental conditions: The corrosivity level of the atmospheric environment's long-term impact on building steel structures can be determined by Table 1.

2. Durability of Corrosion Protection Coating Systems

ISO 12944-1 (2017) divides the design service life of corrosion protection coating systems into four levels. The design life of steel structure protection refers to the lifespan of the coating system before the first major repair, which is when the coating system reaches the Ri3 level of corrosion defined in IS04628.3 (with a rust area of 1%, equivalent to level 6 of ASTM D610), and at this point, the maintenance is most effective and economical. It is important to note that the design service life of a coating system is not a guaranteed period. The design service life assumes that the coating quality, steel structure design, surface treatment, construction standards, construction conditions, and coating application are all fully qualified or meet the requirements, and that the corrosion environment is relatively stable after completion.

3. Coating System and Film Thickness

ISO 12944-5 defines the use of existing coatings and coating systems. In Annex C, tables C.1-C.6 provide examples of coating systems for carbon steel, including primers, intermediate coatings, and topcoats, based on different binders, rust-inhibiting pigments, and dry film thicknesses. Based on the corrosion factors determined in ISO 12944-2, these examples demonstrate the appropriate protective coating systems for various corrosion environments and levels.

I. Graphene Anti-Corrosion Coating for Building Steel Structures

The application of graphene coatings in steel structure buildings demonstrates its unique advantages: the unique two-dimensional structure of graphene gives the coating excellent shielding properties, effectively preventing moisture, oxygen, and corrosive substances from penetrating the steel surface, significantly enhancing the corrosion resistance. Meanwhile, the addition of graphene significantly improves the mechanical properties of the coating, enhancing its impact resistance and wear resistance, making the coating more durable. Graphene coatings are easy to apply, forming an even layer quickly, suitable for various complex steel structure surfaces, simplifying the construction process. Moreover, graphene coatings are free of volatile organic compounds (VOCs), reducing their environmental impact and meeting the requirements for green building standards. Due to the stability and weather resistance of graphene, graphene coatings offer long-lasting protection, reducing maintenance frequency and costs. In conclusion, graphene coatings provide an efficient, durable, and environmentally friendly anti-corrosion solution for steel structures, significantly improving the durability and safety of buildings.

Table I: Anti-Corrosion Coating Scheme for Steel Structure Buildings, High-Speed Rail, and Airports

I. Cold Spray Zinc Coating for Building Steel Structures

Cold spray zinc technology offers numerous advantages for steel structure buildings: It not only provides excellent corrosion protection, effectively preventing steel structures from atmospheric, water, or chemical erosion, but also ensures convenient and efficient application. No heating of the metal substrate is required, allowing for on-site spraying directly onto installed steel structures, reducing disassembly and transportation costs. The coating is uniform and smooth, even covering complex geometric shapes and small gaps to ensure effective corrosion protection. The cold spray zinc coating has a high adhesion to the metal substrate, making it less likely to peel off and stable in various environments. The coating dries almost instantly, enabling rapid use or further processing, thus improving construction efficiency. If the coating is locally damaged, it can be repaired through patching, reducing maintenance costs. During the application process, no harmful gases are emitted, minimizing environmental impact and meeting green building requirements. In conclusion, cold spray zinc technology provides a high-efficiency, convenient, and environmentally friendly corrosion protection solution for steel structure buildings.

Table II: Cold Spray Zinc Coating Corrosion Protection Scheme for High-Speed Rail and Airport Steel Structure Buildings

I. Steel Structure Buildings

Steel structure buildings feature short construction periods, good seismic performance, high safety, large design flexibility, and adaptability to different climatic conditions and atmospheric environments. Additionally, steel structures have minimal construction pollution, low noise, and no dust pollution, making them environmentally friendly buildings. In the late 1990s in China, advanced design theories and techniques in processing, manufacturing, and installation were introduced from abroad, which significantly accelerated the development of steel structure buildings, especially in recent years. High-rise buildings, industrial factories, bridges, elevated interchanges, sports and cultural venues, and other large-scale structures increasingly adopted steel structures. However, the widespread application of steel structures has also exposed several issues, among which corrosion of steel structures is one of the most serious problems.

Table 3: Anti-Corrosion Coating Scheme for Steel Structure Columns, Beams, Trusses, and Frame Structures

I. Renovation of Steel Structures with Graphene Coatings

The application of low-surface treatment graphene coatings in steel structure renovation demonstrates its unique advantages: the two-dimensional structure of graphene provides the coating with excellent shielding properties, effectively preventing moisture, oxygen, and corrosive substances from penetrating the steel surface, significantly improving corrosion resistance. Additionally, graphene coatings can form a strong layer on surfaces that have not been thoroughly cleaned or sanded, greatly simplifying the preparatory work before renovation. The addition of graphene significantly enhances the mechanical properties of the coating, improving impact resistance and wear resistance, making the coating more durable. Graphene coatings are easy to apply, quickly forming an even layer, and are suitable for various complex steel structure surfaces, simplifying the construction process. Moreover, graphene coatings do not contain volatile organic compounds (VOCs), reducing environmental impact and meeting the requirements of green building. Due to the stability and weather resistance of graphene, these coatings provide longer-lasting protection, reducing maintenance frequency and costs. In summary, low-surface treatment graphene coatings offer an efficient, durable, and environmentally friendly corrosion protection solution for steel structure renovation, significantly enhancing the durability and safety of buildings, while greatly simplifying the preparatory work involved in the renovation process.

Table 1: Renovation of Steel Structures, High-speed Rail, and Airports with DreamEnergy Graphene Coating System

The characteristics of steel structure maintenance are as follows:

I. Coating is performed at the work site, with poor working conditions, high-altitude operations, large work volumes inside box beams, high labor intensity, and poor safety.

II. On-site construction usually cannot perform blasting treatments on the surface to be coated, resulting in incomplete rust removal, and sometimes, re-coating over old layers.

III. Due to on-site construction environment and equipment limitations, spraying is generally not possible, and brushing and roller coating are often used.

IV. Surface treatment refers to all preparation work done on the substrate to obtain a high-quality coating. The quality of surface treatment before coating significantly affects the coating's performance. Regardless of the coating type, its performance is directly related to whether the surface treatment of the substrate is correct and thorough. If surface treatment is improper, even the best coating will lose its effectiveness.

Table II: Anti-corrosion solution for steel structure buildings, high-speed rail, and airports using DreamEnergy heavy-duty anti-corrosion coatings

I. Fire Protection Requirements

Currently, steel structures play a unique and increasingly important role in building projects. Due to many inherent characteristics, steel structures are widely applied, especially in high-rise and super high-rise buildings. The use of steel structures for load-bearing purposes has increased. The critical temperature at which ordinary steel structures lose their static stability under full load is around 540°C. Typically, their strength begins to rapidly decline between 300°C and 400°C, and at about 550°C, their strength drops to 50%-60%. The strength variation of steel structures in fire is shown below:

Steel structures fail and collapse rapidly under high temperatures in a fire. Therefore, effective fire protection measures must be taken to extend the time it takes for steel structures to reach the critical temperature. The significance of fire protection for steel structures is as follows:

(1) Reduce damage to steel structures in a fire

Prevent local collapse of steel structures during a fire, which could hinder firefighting and evacuation efforts. The purpose of fire protection for steel structures is to extend the time it takes for the steel structure to reach the critical temperature, allowing more time for firefighting and evacuation.

(2) Prevent overall collapse of steel structures in a fire, reducing casualties

(3) Reduce repair costs for steel structures after a fire

Shorten the recovery period for structural functions after a disaster, and reduce indirect economic losses. Currently, there are many methods for fire protection of steel structures. These methods include passive fire protection techniques such as steel structure fireproof coatings, fireproof boards, concrete fireproofing, internal water cooling of structures, flexible membrane fire protection, etc. These methods provide sufficient fire resistance time, and using fireproof coatings for steel structure protection is the most common approach.

Steel structure fireproof coatings are applied to the surfaces of buildings and structures to form a fire-resistant insulation layer that improves the fire resistance of steel structures. The fire resistance rating refers to the time period in which a building component can withstand fire according to the time-temperature standard curve, starting from the moment of exposure to fire until the component loses its load-bearing capacity, integrity, or fire-resisting function. This is represented in hours.

Fireproof coatings themselves are non-combustible or difficult to ignite. They can prevent combustion or delay the spread of fire, thus providing sufficient time for evacuation and firefighting, ensuring the safety of life and property.

II. Classification, Types, and Standards of Fireproof Coatings

GB14907-2018 "Fireproof Coatings for Steel Structures" classifies fireproof coatings for steel structures.

(1) Fire Resistance Rating

Fireproof coatings for steel structures have fire resistance ratings of 0.50h, 1.00h, 1.50h, 2.00h, 2.50h, and 3.00h.

(2) Product Types

The product code for steel structure fireproof coatings is represented by the letters GT. The characteristic codes for fireproof coatings include: the location code (N for indoor, W for outdoor), the dispersion medium code (S for water-based, R for solvent-based), and the fire protection mechanism code (P for expanding, F for non-expanding). The main parameter code indicates the fire resistance rating.

The model for steel structure fireproof coatings is formulated as follows:

Example 1: GT-NSP-Fp2.00-A, represents: Water-based, expanding type, ordinary steel structure fireproof coating for indoor use, fire resistance rating Fp2.00, fire resistance limit 2 hours, A for custom code by the enterprise.

Example 2: GT-WRF-Ft1.50-B, represents: Solvent-based, non-expanding type, special steel structure fireproof coating for outdoor use, fire resistance rating Ft1.50, fire resistance limit 1.5 hours, B for custom code by the enterprise.

(3) Standards for Steel Structure Fireproof Coatings

The national standards GBJ16-1987 "Building Fire Protection Design Code" and GB5003.5 "Design Code for High-rise Civil Buildings" provide clear regulations on the fire resistance level, combustion performance, and corresponding fire resistance limits of buildings.

III. Selection of Fireproof Coatings

The quality of fireproof coatings directly affects the fire protection performance of steel structures, so the selection of coatings is very important. The selection of fireproof coatings should meet the following requirements: excellent fire insulation performance, fire resistance limits that meet the requirements; high bonding strength between the fireproof coating and the anti-corrosion coating; good weather resistance, water resistance, freeze resistance, no peeling or flaking, long service life; the coatings should be non-toxic and harmless to humans, and should not emit harmful gases during a fire; easy application and reasonable cost.

When selecting fireproof coatings, it is essential to choose one or more fireproof coatings that meet the above performance requirements based on the fire protection objectives and construction requirements.