Despite the growing popularity of alternative piping materials, concrete remains a very popular material when constructing stormwater and sewage systems thanks to its inherent strength, which simplifies installation and backfilling. However, long-term exposure can lead to microbial-induced corrosion (MIC), infiltration/exfiltration, and reduced flow capabilities—outcomes that ultimately affect a project’s long-term success.
In this article, we will explore how engineers can leverage the benefits of the newer piping materials to enhance concrete pipes and protect these infrastructure investments for the long-term. By lining pipes with concrete protective liners (CPL), engineers can combine the chemical resistance and low permeability of thermoplastics, with the raw strength of concrete to create cost-effective and efficient systems.
What are concrete protective liners?
While it is tempting to follow the popular adage of throwing out the old to make way for the new, it isn’t always practical or necessary. Concrete protective liners allow us to keep the advantages of the old while still benefiting from new products. Think of CPL like siding for a house. By placing a protective layer over the concrete, engineers can prevent the pipe’s contents from coming into direct contact with the concrete pipe’s inner walls and thereby avoiding many of the issues mentioned earlier such as MIC.
CPL is not unique in the concrete protection arena, but it does offer some benefits over other methodologies. Another commonly used technique is using a concrete protective spray-on coating. While spray-on coatings are sometimes easier to install than CPL and may seem cheaper, concrete protective liners offer a number of benefits that can make them ideal in place of spray-on coatings. For example, CPL can offer substantial backpressure resistance, enabling it to remain in place in conditions that would cause spray-on coatings to peel away. Therefore, the durability and longevity of CPL will usually outweigh that of spray-on coatings and prove much more cost effective in the long run.
Protecting pipes with CPL
CPL is most effectively used in projects with concrete pipe sizes of 42 inches and above, making it an effective solution for manholes as well as civil sewage and stormwater systems.
Manhole risers represent one of the most significant areas of attack by aggressive wastewater and often require expensive repair work throughout the duration of their service life. Fabricators can create lined manholes using CPL to eliminate infiltration, providing long-term protection and efficient wastewater transmission.
Although engineers typically specify some form of concrete protection for at-risk structures in sewage systems, backpressure can significantly limit the performance of spray-applied coatings. Backpressure in civil sewage systems eventually contributes to inflow and infiltration as the coating is lifted off the concrete surface, allowing aggressive water to reach the concrete. To address this challenge installers can mechanically attach CPL onto the inner surface of concrete pipes in sewage systems. CPL installed in this way will not only protect the concrete from aggressive wastewater, but also will be able to withstand potential backpressure.
Another benefit of CPL is the ability to protect the pipe from biological growth or other buildup within the pipe that could decrease flow capacity of the piping system. CPL made with HDPE can maintain its roughness coefficient throughout its service life, ensuring a consistent flow capacity.