Building outfall sewers to last

HDPE concrete protection liner is solving the age-old issue of concrete corrosion in wastewater treatment works (WWTWs).

Building outfall sewers to last

Anchor Knob Sheet (AKS™) was developed in the early 1990s resulting from a need highlighted in the Western Cape for a long-term solution to the internal protection of large-diameter outfall sewers.

The project in question was a 1 750 mm diameter sewer system in Cape Town. At that stage, pipe protection systems such as dolomitic aggregate, CAC and sacrificial layers were the only options available to engineers in their quest to design a large-diameter sewer pipeline with a life expectancy exceeding 20 years. These cementitious-based options were imperfect in trying to achieve these life expectancies and a new solution had to be found.

Enter AKS™ Thus, the AKS™ product was born. The initial design was a narrow product that required additional welding during installation but this has since been refined and the manufacturing process has been modernised to deliver the AKS™ product available today. AKS™ is a lining system ranging in thickness from 2.0 mm up to 10 mm. It is manufactured from imported, virgin, hexene HDPE resin. The product is extruded in large sheets up to 3.1 m wide and in lengths to suit the particular application.

The success of AKS™ – which has led to it being deployed in many of the world’s largest sewer and WWTW systems – is owed to the unique design of the anchoring system, which firmly holds the AKS™ lining into the concrete structure.

These anchors are formed during the extrusion process (not added on afterwards), making it an integral part of the finished sheet, ensuring that they cannot come free from the sheet even under the harshest operating environments. These anchors are positioned in such a way that a full matrix of anchors is formed – over 1 230 anchors per square metre – ensuring that the liner remains evenly and securely fixed into the concrete.

Pull-off tests have been done over the years to show design engineers that each individual anchor can handle around 35 kg to 40 kg of weight before it pulls free from the concrete. This equates to pull-off strengths of over 40 t/m2 .

The use of AKS™ in large-diameter sewer pipelines has become the norm, with many large projects being completed in South Africa. On a global scale, AKS™ is exported to over 26 countries with nearly 90% of the product – which is manufactured at the modern facility in Cape Town – being exported. Internationally, some of the largest sewer tunnel and pipeline systems have been lined with AKS™, offering these projects the longest possible design life of their lining systems.

Protecting WWTWs The natural progression for AKS™ from the large sewer pipelines was to line WWTWs, as the same aggressive elements in the sewer pipeline create the same damage and corrosion in WWTW structures. Although the installation in a WWTW requires some additional care and attention from the civil contractors, along with the services of a qualified HDPE welding technician, the end result of a well-lined WWTW will offer a municipality or client the knowledge that their structure will be protected for many decades to come.

AKS™ is truly a unique product, both locally and internationally, offering design engineers and clients the opportunity to incorporate the proven chemical resistance properties and exceptional life expectancy of HDPE into a concrete structure of any shape or form. The applications range from pipelines to tunnels, canals, digesters and acid storage tanks to bund areas – and not just in municipal infrastructure projects, but also in mining applications or any industry where aggressive chemicals need to be contained and controlled.

AKS Lining Systems has successfully and reliably secured superior HDPE sheeting technology to an age-old construction material. This is a cross-section view of the AKS™ lined concrete pipe Anchors are integrally formed with the sheet, enhancing the structure’s integrity while protecting the concrete from chemical attack.