By Jimmy Youngblood
Concrete has been a primary construction material for many years because its strength characteristics and established installation practices make it a cost-effective and long-lasting material. However, concrete structures used in sewage systems and water treatment facilities are particularly vulnerable to corrosion and erosion because of the specific conditions of the application. Additionally, the protection of concrete structures against these processes, which can cause infiltration/exfiltration of effluent, has become more serious as retrofit costs, system life cycles, and environmental and health regulations and concerns have increased.
Exfiltration/infiltration in sewer lines can occur because of failures in the sewer pipe caused by cracks or by deterioration of the gaskets between pipe sections. Exfiltration is the process of material moving outside of the sewer system, releasing sewage into the environment, which can pose serious health hazards.
Infiltration deals with liquid entering the sewer pipe via sewer system failure or stormwater runoff, which can lead to sanitary sewer overflows (SSO) by overtaxing water treatment plants.
The U.S. Environmental Protection Agency (EPA) estimates that between 23,000 and 75,000 SSOs occur each year, discharging 3 billion to 10 billion gallons of untreated wastewater. During the next 20 years, $88.8 billion will be required to control SSOs, the EPA said.
The cost of replacing failing sewer pipe is a growing concern among communities that have older sanitary sewer collection systems comprised of concrete pipe. One solution is the use of embedment liners. High density polyethylene (HDPE) concrete embedment and protection liners have benefited the long-term life of a wide range of critical concrete structures in sewer systems.
HDPE embedment lining of concrete pipe addresses corrosion and erosion problems. Corrosion occurs when wastewater collection systems generate hydrogen sulfide, which is absorbed by the moisture in the concrete and converted by bacteria into sulphuric acid that degrades the concrete.
This phenomenon is especially true in applications where there is low flow, and hydrogen sulfide builds up in large concentrations. An HDPE embedment liner can eliminate corrosion because of its chemical resistance, low permeability, and low vapor transmission.
Erosion occurs when sand and particulates in the sewer abrade the concrete. This process is especially a concern in desert areas where there is a high sand content in the sewer and the site has a high-flow system that provides a high abrasion element. HDPE embedment liner is effective because of its high resistance to abrasion.
Fighting corrosion In a project in Strathcona, Alberta, Canada in 2003, sections of the community’s concrete pipe sewer system were bypassed with a separate, HDPE-lined concrete sewer line and HDPE-lined manholes because the system was corroded to the point of failure. Strathcona County’s sanitary sewer line and manholes originally were constructed in 1964 using unprotected concrete. Subsequently, the pipe structures and manholes suffered various degrees of hydrogen sulfide corrosion. Strathcona County needed a sewer system that would withstand the stressful conditions involved and exhibit a longer life cycle.
The project’s first phase incorporated 26, HDPE-lined manholes and 1,225 feet of 42-inch-diameter, HDPE-lined concrete sanitary sewer pipe. The sewer line serves approximately 29,000 people and an additional 489 acres of commercial/light industrial land with a design blended flow generation of 0.208 liters/second/hectare, with an inflow/infiltration rate of 0.50 liters/second/hectare. The Strathcona County project engineer considered two primary options for this project—42- inch-diameter concrete pipe and manholes lined with HDPE; or PVC pipe and 11 new PVC manholes, with all remaining manholes to be standard unlined precast concrete.
Concrete pipe manufacturer Inland Pipe, Calgary, Alberta, was awarded the project and used GSE Lining Technology’s StudLiner. This product has high chemical and abrasion resistance, low permeability, low vapor transmission, and extremely high hydraulic and mechanical pullout strength.
It has successfully protected concrete in wastewater treatment facilities, the power industry, chemical plants, the mining industry, and other industrial applications. For this application, the HDPE embedment liner economically and effectively increased pipe life at a greatly reduced price, compared with pipe replacement.
HDPE’s inherent physical characteristics make it impervious to the aggressive and corrosive materials that can be associated with sewage systems and strong industrial fluids.
The HDPE concrete embedment liners are lightweight, flexible, easily installed by experienced installers, and extremely corrosion and erosion resistant. All joints between embedment panels are welded using standard fusion and extrusion welding practices consistent with geomembranes, offering leak-free and intact seams between panels.
Jimmy Youngblood is Geomembrane product manager for GSE Lining Technology, Inc., Houston, Texas. He can be contacted at 800-435-2008.