Reinforced concrete pipes (RCP) were first brought to North America in the early 1900s and have seen widespread success for sewer pipeline systems. Since then, engineers have developed two design methodologies for installing RCP: indirect and direct design. Indirect design is an empirical system developed in the early 1920s that has worked well in moderate soil covers. In the 1970s, direct design arose from reinforced concrete design theory, which considered other factors affecting the pipe’s long-term performance.
While indirect design is a faster, more straightforward approach, direct design offers a more accurate picture of stresses likely to be encountered by the pipe. Direct design is slowly becoming the prevalent design methodology and has seen widespread use for large diameter pipes and those under high external load conditions (1).
Both design approaches, however, have their utility. To maximize the performance of RCP, engineers should also consider the implementation of concrete protection. This article examines the pros and cons of using RCP, describes how RCP utility can be improved with concrete protection liners (CPL), and explore ways to identify and source high-performing CPL.
Reinforced Concrete Pipes: Pros and Cons
After more than a century of use in North America, RCP has cemented itself as the go-to construction material for most applications. It helps that RCP is also among the most cost-effective material for creating piping systems. Installed pipelines made with RCP have an excellent history of durability when installed in conditions of low-temperature variation and atmospheric exposure. RCP can exceed 100 years of service life if kept in ideal conditions. However, keeping RCP in ideal conditions has proven to be a challenge.
Numerous factors can negatively impact the performance of RCP, including freeze-thaw and weathering, abrasion, acids, sulfates, and chlorides. These do not necessarily affect the pipe’s durability but can alter the performance of the pipe in other areas such as flow capacity (2).
Pitting and abrasion can reduce the smoothness coefficient of the internal surfaces of RCP, which can reduce the pipe’s flow capacity leading to increased pumping costs. Additionally, sewer systems and other pipelines transporting aggressive media can produce byproducts such as sulfates or acids that can corrode the pipe, eventually failing.
Improving Reinforced Concrete Pipes with Concrete Protection Liners
To maximize the performance of RCP, engineers should consider the integration of CPL. CPL is made of flexible, ductile, and corrosive-resistant thermoplastics, providing a robust layer that complements the high strength and stiffness of RCP (3, 4). By lining the inner walls of RCP with a protective barrier, engineers can help keep the pipe in ideal conditions and maximize its service life.
CPL also offers mitigation against common problems without ongoing maintenance or reapplication. For example, CPL helps ensure smooth inner surfaces that do not degrade over time. As explained earlier, materials like RCP have a smoothness coefficient (Manning’s Coefficient) that decreases throughout the pipe’s service life due to fouling or reactions to pipe contents, translating into lower flow capacity and increased pumping costs. By using CPL, engineers can protect the inner walls of the RCP and ensure the best flow capacity throughout the system’s service.
Sourcing your concrete protective liner from AGRU
When looking for the right CPL for your next reinforced concrete pipe project, consider using AGRU’s Ultra Grip. Ultra Grip is a concrete protective liner (in HDPE or PP) that incorporates an innovative anchor design that provides superior mechanical attachment to concrete surfaces, offering high backpressure and pullout resistance. Rated to resist long-term pressures of up to 1.75 bar, Ultra Grip shines in conditions that would otherwise reduce the service life of competing products.
With the streamlined accessibility of Ultra Grip, precasters will be able to produce RCP with enhanced durability and longevity. AGRU’s drop-in specifications make it easy for your engineer to incorporate Ultra Grip into the design. Additionally, our variety of product configurations, roll widths, and sheet sizes help make fabrication easier and increase yield by minimizing the loss of materials.
- 1. “Reinforced Concrete Pipe.” American Concrete Pipe Association. Presentation. Accessed online 28 February 2022 http://www.concretepipe.org/secure/tracks/2018/Engineering:Technical%20Marketing:Sales/IndirectDirectDesign_Braun.pdf.
- 2. “Precast Concrete Durability.” American Concrete Pipe Association. (2016). Accessed online 28 February 2022. https://www.concretepipe.org/wp-content/uploads/CPInfoDurability072116.pdf.
- 3. Erdogmus, B. N. Skourup, and M. Tadros “Recommendations for Design of Reinforced Concrete Pipe.” J. Pipeline Sys. Eng. Prac. (2010). Accessed online 28 February 2022 https://ascelibrary.org/doi/full/10.1061/%28ASCE%29PS.1949-1204.0000039.
- 4. Green. “Manufacture of Concrete Pipes Using CPL Technology.” Geo-Frontiers Congress. (2011). Accessed online 28 February 2022. https://ascelibrary.org/doi/pdf/10.1061/41165%28397%29195.