Corrosion Proof Polymer Concrete Manholes & Structures: Where to Use Them in Design & Why

There are a lot of discussions in the engineering community about corrosion-proof polymer concrete manholes and structures. Are they really that great? Does it make sense to use them in design? 

In this article, we will cover the basics of corrosion-proof polymer concrete, where to use them in design, the benefits they offer, and more. To help make this article more accessible, we’ve also included a section on life cycle cost analysis and polymer concrete specification.

What is Corrosion?

Corrosion is a major problem in wastewater  systems because of the presence of hydrogen sulfide gas. This gas is generated by Thiobacillus Bacteria which oxidizes to form sulfuric acid. The sulfuric acid then attacks the cement which acts as the glue holding the aggregates together, causing the concrete to deteriorate. Aggregates are also susceptible to corroding in most concrete structures. Once corrosion begins, the integrity of the entire structure is at risk which can lead to collapse.

corroded concrete manhole
Example of a corroded concrete manhole due to H2s gas

Typical Band-Aid Fixes for Corrosion

Rather than address the problem of corrosion at the source most of the industry attempts to stop corrosion through what we term as band-aid fixes. We call them band-aids because they don’t actually solve the problem. It’s kind of like putting lipstick on a pig.  Here are three of the most commonly used methods:

1. Coatings

There are many different brands of coatings across the country and many companies that offer them. The most common type of coating used are epoxies and polyurethanes.

  • Epoxy Coating: An epoxy coating is a coating compound that consists of two elements: the epoxy resin and polyamine hardener. When mixed, a chemical reaction causes the two compounds to cross-link and form a very strong bond. 
  • Polyurethane Coating: PU paint or the PU coating is a coating that is used in many industries, including architecture and industrial systems.

A spray-on application is the most common way to apply these coatings and the most common specification is about 125 mils or an eighth of an inch thick.

While these coating materials themselves stand up well to corrosion the problem is they are adhering to a corrosive substrate. It doesn’t matter how good the coating is applied there is still potential for corrosion to happen due to the corrosive substrate. Over time the most common way that coatings fail is by pinholes or delamination. It is also important to remember that a visual inspection is not enough to determine if corrosion is happening or not. Many times corrosion happens behind the coating so while the lipstick might look good on the outside, you are still applying that lipstick to a pig!

2. Cast In Liners

Cast-in liners are sometimes used and installed on a precast concrete structure. These structures come precast with the liner installed at the factory. A professional installer will then come to the field and weld or melt the joints of the liner to ensure a watertight seal. The two most common types of cast-in liners are: PVC and HDPE.

In a similar fashion to coatings, liners also fail because they are adhering or being installed on a corrosive substrate. The most common failure mode is delamination from a concrete structure. In some cases there have been disasters of failed liners delaminating from concrete structures and blocking sewage flow. 

3. Admixtures

Admixtures are basically a compound that is mixed in a concrete mix that claims to have antimicrobial properties that will kill bacteria that causes corrosion and prevent it from ever happening again. The reason why we include this type of solution as a band-aid fix is because it is not entirely proven.

While band-aid solutions can offer some level of protection, they are not foolproof and often do not address the root cause of the problem. Make sure not to design with band-aid solutions in mind because they are not a long-term fix.

Polymer Concrete Material Properties

Now let’s talk about corrosion-proof polymer concrete and how it can stop the corrosion problem. Polymer concrete is a material made from non-reactive sand, non-reactive aggregate, and polyester resin. The resin acts as the glue or binder that holds everything together. Everything in the matrix is completely inert or corrosion proof including the reinforcement.

At Armorock, we have made this solution accessible and affordable for everyone. All the structures made by Armorock are designed and sealed by professional engineers and carry HS-20 traffic rated loading. Polymer Concrete is not a band-aid fix because everything from the resin to reinforcement is corrosion-proof and sustainable.

Material Strength Properties of Polymer Concrete

  • Compressive strength of 16,000+ psi
  • Flexural strength of 2,200+ psi
  • FRP Rebar used for reinforcement per ACI 440

Corrosion Proof Polymer Concrete Applications

The good thing about Armorock’s polymer concrete is that we cater to both circular and non-circular applications. From four foot to sixteen foot diameter cylinders to custom box structures, we have the capability to produce a variety of shapes and sizes. All designs that a traditional precast concrete supplier could create, we can create with polymer concrete. We see no limit to the possibilities of what can be accomplished with our product.

A common question is “where is polymer concrete typically specified?” The easiest answer is anywhere you are currently calling out some form of corrosion protection. Some of the most common structures specified are:

Pump Stations

A pump station works by collecting sewage or wastewater from houses and buildings then storing it in a chamber where it is pumped to a treatment plant. When a certain level of collected wastewater is met, the sewage is lifted through a discharge system.

armorock pump station
Example of an Armorock Pump Station (12’ diameter that is 40’ deep in CA)

Wet Wells

Wet wells are a portion of the water and wastewater pumping station. It is the part of the station that stores the sewage or wastewater until it is pumped out.

Other Common Applications

  • Force main discharge manholes
  • Downstream manholes from a lift station
  • ARV Manholes
  • Drop manholes or manholes with “beaver” slides 
  • Junction box or diversion structures
  • Siphon structures
  • Trunk lines or outfall lines
  • Outside of wastewater also many industrial applications (polymer concrete is good on a Ph from 1-13) 
  • Plus many applications others not listed here 

Life Cycle Cost Analysis and Polymer Concrete Specification

LCCA or the life cycle cost analysis is the process of determining the total cost of ownership of a product or system. The aim is to find the most cost-effective solution that meets the needs of the customer both in the short and long term. Armorock has a downloadable LCCA Tool that can help you determine the cost of our product compared to traditional concrete. This way, you can make an informed decision as well as ensure the sustainability of your future budgets.

Learn More About Armorock’s Polymer Concrete Options

Interested in learning more about Armorock and its corrosion-proof polymer concrete solutions? Are you planning a project that could benefit from our material? Discover why owners that are looking for a lasting and sustainable system are choosing Armorock. Have the benefit of a 50-year corrosion warranty for the life of your project and more.

Contact Armorock today and discuss your project with one of our corrosion experts!