Enhancing sewer pipe durability with thermoplastic concrete protective liners

Concrete pipes have been used in sewer construction for decades due to their high load-bearing capacity, dimensional stability and cost-effectiveness. In wastewater systems, however, they are exposed to complex loads that significantly affect their durability. In addition to mechanical loads resulting from soil cover and traffic, aggressive chemical media and biogenic corrosion processes act on the internal pipe surfaces. Particularly in combined and sanitary sewers with elevated sulfide potential, biogenic sulfuric acid corrosion represents one of the main causes of damage.

Mechanisms of biogenic sulfuric acid corrosion

In oxygen-depleted areas of wastewater, sulfate-reducing bacteria generate hydrogen sulfide (H₂S). This gas diffuses into the sewer atmosphere and is converted into sulfuric acid (H₂SO₄) by sulfur-oxidizing microorganisms at the moist pipe crown. The acid attacks the cement matrix, leading to decalcification of the binder and, consequently, to a loss of cross-section. Under these conditions, unprotected concrete surfaces may exhibit a significantly reduced service life, making extensive rehabilitation measures necessary.

Structural bond between concrete and plastic lining

The Agru Ultra‑Grip concrete protective liner system adopts a structural approach to enhancing the durability of concrete structures. During manufacture, a chemically resistant thermoplastic liner is integrally bonded to the concrete. The large number of AGRU Ultra‑Grip anchor studs (≈ 420 pcs/m²) provides a mechanically interlocked bond between the liner and the concrete, reliably preventing delamination and the ingress of media at the interface.

Unlike retrofitted coatings or liners, the result is a composite in which the concrete fully fulfils the load‑bearing function, while the thermoplastic layer serves as a durable protective and functional layer. The system remains leak‑tight even under varying load conditions and thermal influences.

Resistance and hydraulic properties

The thermoplastic liner offers high resistance to biogenic and chemical attack and provides long-term protection of the concrete against corrosion. At the same time, its smooth inner surface exhibits significantly lower roughness than untreated concrete, leading to improved hydraulic performance, reduced energy losses, and a lower tendency to deposit build‑up.

For sewer operation, this translates into more stable flow conditions and extended cleaning intervals. During planning, these properties can be utilized either to increase the capacity of existing systems or to optimize the design of new pipelines.

Service life and cost‑effectiveness

By combining structural load‑
bearing capacity with effective corrosion protection, precast concrete pipes lined with Agru Ultra‑Grip concrete protective liners achieve a very long service life. The reduction in corrosion‑related damage minimizes maintenance and rehabilitation work and lowers life‑cycle costs. This has a particularly significant impact on the economic efficiency of municipal drainage systems, especially for large‑diameter wastewater collectors.

Field experience

Several Andalusian cities, including Seville and Fuengirola, have successfully implemented concrete pipes lined with Agru Ultra‑Grip concrete protective liners. Applications range from the refurbishment of existing pipelines and the replacement of heavily stressed collectors to the extension of municipal sewer networks. These projects demonstrate that the composite system performs reliably even under challenging climatic and chemical conditions and contributes to the long‑term safeguarding of infrastructure.

40 years of AGRU concrete protective liners

In 1986, Agru introduced the world’s first anchored concrete protective liner. With 40 years of continuous development and field experience, Agru remains the original pioneer and benchmark for durable concrete protection. Our systems help ensure structural integrity in potable water tanks and reservoirs, wastewater treatment structures, industrial facilities, and other concrete exposed to chemical or mechanical stress.

Conclusion

Concrete pipe systems with thermoplastic liners provide a technically mature solution for enhancing the durability of wastewater infrastructure. The Agru Ultra‑Grip concrete protective liner combines the proven mechanical properties of concrete with a highly resistant protective layer, thereby meeting the key requirements for modern, long‑lasting, and cost‑efficient drainage networks.