What material is commonly used for manhole covers?

Manhole covers are typically made from cast iron due to its advantageous properties. Cast iron is known for its strength and durability, which makes it ideal for withstanding heavy loads and the stresses associated with vehicular traffic. Additionally, it has excellent resistance to corrosion and wear, ensuring a long lifespan even in harsh underground environments.

The use of cast iron also allows for a significant weight, which helps to keep the covers securely in place and prevents them from being easily removed or displaced. This factor is particularly important for safety, as loose or improperly fitted manhole covers can pose hazards to pedestrians and vehicles.

Other materials, while potentially useful in certain situations, do not offer the same combination of strength, durability, and cost-effectiveness that cast iron provides. For instance, aluminum may be lighter but is not as robust under heavy loads, while plastic lacks the necessary strength and resilience for the demands of a manhole cover. Steel can be used for manhole covers but is often more prone to corrosion unless properly treated. Thus, cast iron remains the most common and practical choice for manhole covers in infrastructure applications.