Post-Tensioned Pools & Tanks

Why use post-tensioning for hydraulic structures?

Pools, water tanks, and treatment basins must guarantee absolute watertightness throughout their service life. In conventional reinforced concrete, tensile stresses inevitably cause micro-cracks through which water seeps. The standard solution is to add a waterproofing membrane (PVC, EPDM, or geomembrane) — an additional layer that is costly, fragile, and requires regular maintenance.

Post-tensioning fundamentally transforms the behaviour of the concrete by keeping it under permanent compression in all directions. In the absence of tension, no cracks can form: the concrete itself becomes the guarantor of watertightness. This approach eliminates the need for a membrane in most configurations, reducing construction costs and, above all, maintenance costs over 50 years and beyond.

How does a post-tensioned tank work?

A post-tensioned tank consists of a base slab and walls (vertical panels) prestressed by cables arranged horizontally (to resist the water pressure) and vertically (to resist bending at the wall base). The horizontal prestressing is the most critical: it must maintain a minimum residual compression of 1 MPa in the concrete under maximum hydrostatic pressure.

For circular tanks, post-tensioning is particularly effective because the annular geometry allows uniform compression of the walls using circumferential cables. Rectangular tanks require more complex design to manage stress concentrations at the corners, but post-tensioning remains far superior to conventional reinforced concrete for large volumes.

Advantages over conventional solutions

The intrinsic watertightness of compressed concrete is the decisive advantage. While a PVC membrane has a service life of 15 to 25 years and requires regular inspection, a properly designed post-tensioned structure remains watertight for over 50 years without intervention. For a 5,000 m³ potable water tank, the saving on the membrane and its replacement amounts to 30 to 45% of the structural cost over the full life cycle.

The reduction in wall thickness (20-25% less than in reinforced concrete) decreases the volume of concrete and the loads on the foundations. For buried structures, this weight reduction facilitates construction and lowers the risk of uplift from the water table.

Compliance with international water-retaining standards (EN 1992-3, ACI 350) is more readily achieved with post-tensioning, because the crack-width limitation criterion is automatically satisfied by the permanent compression state. For potable water tanks, post-tensioning eliminates the risk of contamination from infiltration through cracks.

Typical applications

BEPCO designs and builds Olympic and leisure pools, potable water tanks from 100 to 50,000 m³, water towers, wastewater treatment basins, industrial tanks, and aquariums. Our structures comply with international standards and are adapted to the climatic conditions of West Africa.