Polyurea-based coating technology for corrosion protection in construction and technical infrastructure

1. General Introduction

Vietnam is a country with a hot and humid tropical climate. It has a coastline of over 3,260 km stretching from North to South. This environmental condition causes rapid corrosion of metal structures and corrosion and destruction of reinforced concrete structures (RCS) at a very high rate. According to survey data from the Vietnam Association of Corrosion Science and Metal Protection, corrosion damage in our country is no less than 5% of GDP. Thus, it can be seen that the economic loss in our country annually reaches up to 20-25 billion USD due to corrosion, which is indeed a significant loss. The damage caused by corrosion worldwide is also substantial; in the United States alone, this loss amounts to several hundred billion USD annually.

Therefore, protecting against corrosion for metal structures and reinforced concrete structures (RCS) to extend the lifespan of constructions plays a very important role in the economy. To combat corrosion of metals and RCS, various measures can be applied, including:

• Choosing suitable structural steel materials with high corrosion resistance for the working environment.
• Using methods to alter the corrosiveness of the environment, including the use of corrosion inhibitors.
• Selecting and using high-durability coatings with high mechanical strength.
• Electrochemical protection.
• Enhancing the properties of concrete and the thickness of protective layers for rebar or coated rebar in coastal atmospheric regions, or applying coatings for RCS exposed to chemical environments or chloride ion environments.

In practice, the use of coating materials is a very common method that has been around for a long time and is a crucial measure in combating corrosion for metals. It is often combined with coatings and electrochemical protection (cathodic protection) in specific cases such as steel pipelines or underground steel storage tanks. For above-ground pipes and tanks, coatings are combined with corrosion inhibitors. Preventing corrosion in RCS, often involves increasing the thickness of the protective concrete layer around the rebar enhancing the properties of the concrete, or applying a protective composite layer. Therefore, the choice of protection measures must be carefully considered from the design stage of the construction. In other words, selecting protective coating materials against corrosion is particularly important as it determines the lifespan and investment effectiveness of the construction.

2. Conditions for Metal Corrosion and Destruction

The main agents causing metal corrosion are the presence of both water and oxygen. Steel (Fe-C) equipment and pipelines that come into contact with water (or water vapor) and oxygen typically undergo the following reactions:

• 3Fe+4H2O=Fe3O4 iron rust +4H2↑3Fe+4H2​O=Fe3​O4​ iron rust +4H2​↑
• 3Fe+2O2=Fe3O4 iron rust 3Fe+2O2​=Fe3​O4​ iron rust 

Alternatively, redox reactions may occur in an electrolyte environment (such as soil with low resistivity, acids, bases, salts, etc.), resulting in the formation of Fe3O4⋅nH2OFe3​O4​⋅nH2​O (iron rust). This process generates a corrosion current, leading to a faster corrosion rate. In some cases, steel corrosion can occur even in the absence of oxygen, particularly in the form of sulfide corrosion. Sulfur is produced by microorganisms that decompose organic impurities.

3. Conditions for Corrosion and Destruction of Reinforced Concrete Structures (RCS)

• Corrosion of rebar in concrete occurs in the presence of chloride ions: Water vapor, oxygen, and chloride ions from the environment penetrate the area of concrete near the rebar. Free chloride ions will diffuse within the concrete structure according to Fick’s Second Law. The higher the temperature differential, atmospheric pressure, water vapor, and chloride content, the faster the diffusion occurs. The higher impermeability of concrete reduces the diffusion of chloride ions. When the chloride ion content in concrete reaches 0.6 to 0.8 kg/m³, it breaks down the passive protective layer of the rebar, allowing moisture and oxygen to quickly initiate corrosion reactions that destroy the metal, as mentioned in section 2 (Conditions for Corrosion and Destruction of Metals). When rebar rusts, its volume increases by 4 to 6 times, leading to cracking or breaking of the concrete. The phenomenon of corrosion and destruction of RCS in coastal atmospheric regions in Vietnam is very common and alarming. Most construction projects in coastal atmospheric regions of Vietnam show signs of corrosion after 15 to 20 years. Many constructions experience severe corrosion and destruction after 30 years of use, posing safety risks.

Electrochemical corrosion mechanism of steel in concrete in the presence of chloride ions

• Corrosion of RCS in submerged areas (seawater, brackish water, freshwater) often involves reactions between minerals in concrete (cement stone) with magnesium salts (Mg) or sulfate salts. Alternatively, it may involve leaching reactions or microbial corrosion.
• Corrosion of RCS in industrial facilities and drainage infrastructure is a prevalent form of corrosion in our country today, causing significant economic losses for investors. This is primarily due to RCS (existing as storage tanks, pipelines, floors, etc.) being directly exposed to strong corrosive agents in manufacturing plants and wastewater. Some corrosive agents include: SO₂; H₂S; CO₂; PAC chemicals; chlorine chemicals; and cleaning agents… When RCS comes into contact with these chemicals, chemical corrosion usually occurs through acid-base neutralization reactions that cause rapid deterioration (decay) and destruction of the concrete. Many industrial construction projects and drainage infrastructure suffer severe corrosion and destruction just after 5 to 7 years of operation if no appropriate anti-corrosion measures are implemented. For steel storage tanks in metallurgical and chemical industries, although they are protected against corrosion from the time of construction, most require the replacement of protective coating layers every 3 to 4 years.

4. Some construction projects and technical infrastructure that have suffered from corrosion and damage in Vietnam

Recirculating water pipeline D1400, 1.5 km long

• Project: Uong Bi Thermal Power Plant
• Investor: Uong Bi Thermal Power Plant
• Current damage: After 30 years of operation, the 2mm thick steel pipe surface is heavily corroded, with many holes.
• Corrosion agent: due to brackish water containing high chloride content
• Repair solution: Clean rusted steel, and patch holes. Paint 2mm thick anti-corrosion polyurea.

D800 wastewater pipe 1.5 km long

• Project: Bau Bang Industrial Park
• Investor: Becamex Group
• Current state of damage: After 15 years of operation, the surface of the concrete pipe is heavily corroded, with many holes and water leaks.
• Corrosive agent: wastewater containing organic substances that decompose to create highly corrosive substances such as H2S
• Repair solution: Clean concrete, and patch holes. Apply 2.5 mm thick anti-corrosion polyurea paint.

Binh Hung Wastewater Treatment Plant

• Project: Binh Hung Wastewater Treatment Plant
• Investor: Technical Management Center – Ho Chi Minh City
• Current damage: After more than 10 years of operation, the concrete surface of the submerged part is heavily corroded, leaving exposed stone. The steel reinforcement is rusty. The tank is leaking a lot.
• Corrosive agent: chemicals put into the tank to treat and clean the wastewater.
• Repair solution: Clean the concrete, and patch the damage. Apply 2mm thick anti-corrosion, waterproof polyurea paint.

Water pumping station

• Project: Water pumping station
• Investor: Tan Hiep Water Plant – Ho Chi Minh City
• Current state of damage: After 25 years of operation, the reinforced concrete floor and beams are severely corroded. Concrete beams are cracked and peeling.
• Corrosive agent: chlorine chemicals are added to the water source to disinfect before pumping clean water into the system
• Repaired solution: Clean concrete, and patch damage. Reinforce structural steel. 3mm thick anti-corrosion, waterproof polyurea paint.

5. Polyurea coating technology protects against corrosion

Underground pipelines, when designed and installed, typically require a minimum lifespan of over 50 years, and for Class 1 projects, the requirement is over 100 years. Maintenance and repair of underground pipelines are very costly and sometimes impractical due to land clearance conditions, deep underground locations, and difficulties in dismantling and replacement. Therefore, any damage caused by corrosion is something users do not desire and can result in significant economic losses.For steel tanks or reinforced concrete structures (RCS) that come into contact with chemicals or corrosive agents, it is mandatory to apply a protective anti-corrosion coating. One of the preventive measures from the outset is for users, especially designers, to select the most suitable coating (the primer for the structure) that has the highest mechanical strength, chemical resistance, impermeability, and longevity.

Anti-corrosion coatings typically require the following properties:

• High impermeability (to water, oxygen, chlorine vapor, etc.);
• Good electrical insulation and electrochemical properties;
• High adhesion to steel or concrete surfaces;
• High mechanical strength, UV resistance, and chemical durability;
• Good impact resistance;
• Scratch and abrasion resistance to protect against damage during handling, testing, transportation, installation, and operational activities;
• Ability to withstand ground movement and thermal stress;
• High crack resistance (high crack bridging ability) and high elongation.

Various types of coatings are currently used worldwide to protect underground pipelines, steel structures, and storage tanks, including:

• Bituminous Coating: This type of coating has been used for a long time. Its advantages include low cost, while its disadvantages are low durability, poor impact resistance, and susceptibility to scratches during installation, as well as containing toxic solvents. Currently, this type is very limited and rarely used globally.
• Polyester/Vinyl Ester Resin Combined with Fiberglass to Form Composite: This is widely used and easy to apply. However, it has drawbacks such as poor impact resistance, brittleness, susceptibility to cracking, inability to withstand thermal shock, very poor UV resistance, and high toxicity. Its outdoor lifespan is typically less than 5 years.
• Epoxy-based Paint: This is also commonly used and easy to apply. The downsides include poor impact resistance, brittleness, susceptibility to cracking, and inability to withstand thermal shock. The lifespan of epoxy is generally under 10 years.
• Polyethylene Jacketing: This method involves wrapping the pipeline with an outer layer, leaving many joints. The polyethylene wrap can be damaged during installation. It becomes soft at 80 °C (176 °F) and melts at temperatures close to 100 to 110 °C (212 to 230 °F). It cannot be applied inside the pipeline; therefore, its application is limited.
• Polyurea Coating: Polyurea is a high-performance coating developed from modified polyurethane, which has been around for over 80 years. It has been widely used globally for about the last 30 years in various industries such as oil and gas, water supply and drainage, civil construction, and hydropower. In Vietnam, polyurea has been used for protecting pipelines, water tanks, and waterproofing roofs for nearly 20 years. This coating can be considered the perfect solution of the 21st century due to its many superior advantages compared to all other coating systems. The lifespan of polyurea coatings in soil or submerged conditions is over 50 years; in outdoor conditions over 20 years; in marine environments over 15 years; and in industrial environments exposed to chemicals over 8 years.

Polyurea coatings have several advantages over other types of coatings, including:

• Fast Curing: Polyurea cures quickly (from 5 seconds to 120 seconds depending on user requirements). It can be used and exposed to water just 60 seconds after spraying, ensuring economic efficiency with high production rates and reduced waiting times or production downtime for repairs.
• High Adhesion: It has excellent adhesion to surfaces such as steel, concrete, wood, and plastic, creating a seamless, joint-free coating.
• Superior Impact Resistance: Polyurea offers the highest impact resistance among coating systems.
• High Chemical Resistance and Corrosion Protection: Polyurea exhibits excellent resistance to chemicals and corrosion.
• High Crack Resistance: It has a high crack bridging ability, accommodating cracks up to 5 mm.
• High Tensile Strength and Elasticity: With a tensile strength comparable to one-tenth that of steel and an elasticity exceeding 350%, it can withstand significant stress.
• Reduced Hydraulic Losses: The smooth inner surface of the pipeline minimizes hydraulic losses.
• Long-term Economic Efficiency: The low erosion wear leads to prolonged economic viability.
• No VOCs: Polyurea contains no volatile organic compounds, making it safe for human contact and food applications.
• Chemical Resistance in Industrial Applications: In industrial or wastewater pipelines, polyurea can withstand attacks from chemicals such as chlorides, alkalis, and acids, ensuring a longer economic lifespan compared to all traditional coating systems.

Some tests on the durability of polyurea materials were produced and tested by the Polyurea and Paint Factory of NewTec Group Joint Stock Company under the witness of many construction industry experts.

Spray polyurea on a lightweight concrete wall to test impact resistance

Using a hammer, the concrete wall broke but the polyurea layer remained intact

Spray polyurea on Fibro cement sheet to test the durability of the polyurea membrane

If a car is driven over a non-polyurea-coated fiberboard, it will shatter. A polyurea-coated panel will retain its original shape

6. Some projects using polyurea coating for anti-corrosion and waterproofing implemented by NewTec Group in Vietnam

Over the years, NewTec Group Joint Stock Company has implemented anti-corrosion and waterproofing construction for many large-scale and important projects in the country. Projects with high requirements for anti-corrosion factors have used super durable polyurea-based coating materials. Polyurea products are carefully tested and evaluated for quality at specialized laboratories licensed by the Ministry of Construction. NewTec Group’s construction always meets the technical requirements, quality, and progress of the project.

Providing materials and equipment for polyurea coating technology to protect against corrosion of D800 & D1200 concrete pipes at Ha Thanh Concrete Factory

Polyurea coating protects against corrosion of 1.5 km long D800 concrete pipeline

Polyurea coating protects against corrosion of single-unit wastewater treatment tank A-B

Polyurea coating protects against corrosion of VonFram tanks

Polyurea waterproofing for the roof of the Government Office

7. Conclusion

• Choosing an anti-corrosion coating is one of the optimal measures to prevent corrosion for structures in strong corrosive environments. Specifically, choosing an anti-corrosion protective coating for buried pipelines, steel structures or chemically exposed tanks is especially important. To ensure economic and technical efficiency as well as ensure the life of the project. Polyurea-based coating materials are currently the most optimal choice for long-term anti-corrosion protection for buried pipelines, steel structures and tank structures. The high life of polyurea in corrosive environments will minimize the damage caused by corrosion. And will bring high economic benefits to investors and to the whole society.
• Choosing super durable polyurea-based coating materials for waterproofing and anti-corrosion for construction works and technical infrastructure is a popular trend in the world and Vietnam today. The disadvantage of polyurea material is that the price is about 1.2 times higher than traditional coatings and the construction must be done by a specialized machine that heats 2 components at high pressure, operated by a team of workers trained in polyurea spraying.
• NewTec Group is proud to be a polyurea manufacturer and a leading provider of solutions and services for new-generation coatings in Vietnam. We always improve technology and improve quality management of the production system of waterproofing and anti-corrosion coatings to protect the works of all investors, ensuring long-term durability and the highest economic efficiency.