Road infrastructure is incomplete without proper manholes positioned in strategic areas. And the proper manhole system always has high-quality manhole covers providing protection for underground utilities, sewers, and cables.

The choice of material for manhole covers plays a crucial role in ensuring safety, durability, and performance under varying conditions. Among the most popular materials for manhole covers are ductile iron and fiberglass reinforced polymer (FRP). 

Both materials have their own set of advantages and limitations. In this post, we will dive into the topic of ductile iron vs. FRP manhole covers.

 

Material Composition

 

Ductile Iron:

Ductile iron is a type of cast iron known for its high tensile strength and excellent ductility. It is created by adding small amounts of magnesium to molten iron, which results in the formation of graphite nodules. This modification gives the material high flexibility, making it stronger and more resistant to cracking than traditional cast iron.

 

FRP (Fiberglass Reinforced Polymer):

On the other hand, FRP (Fiber Reinforced Polymer) manhole covers are made from a composite material that combines fiberglass and resin. The fiberglass provides strength, while the resin binds the fibers together, creating a durable, lightweight cover. The result is a corrosion-resistant, non-metallic cover with specific applications where weight and corrosion resistance are critical.

 

Strength and Durability

 

Ductile Iron:

Ductile iron is renowned for its high load-bearing capacity. It can withstand extreme pressure and heavy traffic, making it an ideal choice for urban streets, highways, and areas with high vehicle loads. The strength and durability of ductile iron covers that allows them to resist deformation and cracking even under substantial weight. As a result, ensuring a longer lifespan.

 

FRP:

While FRP covers are not as strong as ductile iron, they still offer impressive load-bearing capabilities. Especially in light to medium traffic areas. FRP manhole covers are suitable for residential areas, parks, and pedestrian zones where heavy traffic is not a primary concern. However, they may not withstand the same levels of impact or load as ductile iron in high-traffic or industrial settings.

Weight

 

Ductile Iron:

Ductile iron manhole covers are significantly heavier than their FRP counterparts. This weight gives them added stability and makes them more difficult to remove or tamper with. The covers’ heavy weight can be an advantage in certain security-sensitive applications. However, the added weight also makes ductile iron covers more challenging to handle and install.

 

FRP:

FRP manhole covers are lightweight in nature. They are much lighter than ductile iron, making them easier to transport and install. This can be particularly beneficial in areas where ease of handling and installation are important. Additionally, the lower weight can reduce installation costs and labor time.

 

Corrosion Resistance

 

Ductile Iron:

While ductile iron is generally durable, it is susceptible to corrosion when exposed to moisture, chemicals, and harsh environmental conditions. Over time, the cover may rust, especially in areas with high humidity or exposure to de-icing salts. To combat this, ductile iron covers are often coated with a layer of bitumen, epoxy, or paint. Coating them with these agents provides some degree of protection against corrosion.

 

FRP:

FRP is highly resistant to corrosion and does not rust or degrade over time. This makes FRP manhole covers ideal for areas with high moisture. They are ideal to be installed in areas such as coastal regions, or environments with corrosive substances like chemicals, acids, and oils. The non-metallic nature of FRP ensures that it maintains its strength and integrity in corrosive conditions. Therefore, offering a much longer lifespan in such environments.

 

End Thoughts

 

Now that you are aware of the differences, it is time to assess your priorities and choose wisely. Rather than approaching two options as ductile iron vs. FRP, focus on each material's qualities and see which aligns best to your needs.

At Dutco Tennant LLC, we have both the options available. Connect with us to discuss your project requirements and choose the right product that meets your demands