Why do iron bridges use zinc coating?

a) Cost effective

b) Prevention of corrosion

c) Increasing strength

d) Improve electrical conductivity

Answer: Prevention of corrosion

Iron bridges use zinc coating primarily to prevent rust and corrosion, which helps maintain their strength, durability, and safety over time. Zinc coating is cost-effective, long-lasting, and ensures that the iron structure remains protected from moisture and environmental damage.

Iron is widely used in bridge construction because of its high tensile strength, toughness, and ability to bear heavy loads. It is a strong, hard, and durable metal that can resist stress, strain, and weight effectively, making it ideal for large structures like bridges. Additionally, iron is widely available and cost-effective compared to many other construction materials.

However, iron has one major drawback — it undergoes rusting when exposed to moisture, water, and air. Rusting converts strong iron into a weak, flaky powder, reducing its strength and making the structure unsafe over time. This corrosion weakens the physical properties of iron, compromising the safety and lifespan of bridges.

Role of Zinc Coating (Galvanization) in Preventing Rust

To protect iron bridges from rusting and corrosion, a zinc coating is applied through a process called galvanization. Zinc serves as a protective shield that prevents iron from coming into direct contact with air and moisture. Even if the coating gets damaged, zinc offers sacrificial protection by corroding itself before iron does. This greatly extends the life of the iron structure.

Benefits of Zinc Coating on Iron Bridges

• Prevents Corrosion: The primary function is to stop rust and maintain structural strength.
• Cost-Effective: It is cheaper to apply zinc coating than to repair or replace rusted iron parts.
• Preserves Strength: While zinc does not increase the strength of iron, it helps retain the original load-bearing capacity by preventing degradation.
• Durability: Galvanized bridges can last for decades with minimal maintenance.
• Low Reactivity: Zinc reacts less aggressively with environmental elements, offering long-term protection.

Other Methods of Protecting Iron From Rust

• Painting: Creates a barrier to prevent moisture contact.
• Electroplating: Deposits a thin protective metal layer.
• Galvanizing: The most durable and commonly used method for bridge construction.