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External prestressing

Non Destructive Tools tools and innovative solutions for inspecting and monitoring external prestressed cables

External prestressing cables are essential elements in both new structures and strengthening works for existing assets. Because they contribute directly to structural performance, they must be regularly inspected and monitored.

Sixense offers a specialised portfolio of solutions to assess the condition of external prestressing cables, including the measurement of residual tension and the detection of wire or strand breaks. These tools help identify deterioration that may not be visible externally.

Our experts support asset owners and engineers in designing and implementing tailored inspection programmes. This ensures hidden defects are detected early and enables the safe, long‑term management of externally prestressed structures.

Our techniques and expertise in external prestressing

Escan

Detection of voids and white paste in external post-tensioning sheaths

Escan technology, developed in partnership with Université Gustave Eiffel (UGE), uses a capacitive probe made of two electrodes forming a capacitor. The device measures variations in capacitance caused by changes in the dielectric properties inside the HDPE conduit, allowing the detection of anomalies.

The inspection unit fully surrounds the sheath and is moved along the cable to identify injection defects or irregularities within the duct.​​

Uscan

Detection of wire breaks in the anchorage zone using ultrasonic reflectometry

The ultrasonic reflectometry method uses high‑frequency mechanical waves generated by a transducer placed against the end of the wire being tested. These guided waves travel along the wire and reveal damage by identifying changes in the signal and estimating the location of any discontinuities.

The patented Uscan technology, co‑developed with UGE (Université Gustave Eiffel), is the only solution capable of assessing the condition of prestressing strands within the anchorage zone.

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ITscan – Anchoring

Inspection of anchor caps using active infrared thermography

This Sixense‑patented method identifies injection defects by applying controlled thermal stress using a custom‑made inductor positioned against the anchor cap.

Once the thermal load is stopped, the resulting thermographic images are analysed to locate voids—whether filled with cement grout or petroleum wax—and to detect the presence of water if present. This non‑destructive technique provides a reliable way to assess the condition of anchor caps and verify the quality of injections.​

ITscan – Sheath

Inspection of sheaths in the main section using active infrared thermography

As with anchor caps, this method detects injection defects along the main length of prestressing cables by applying controlled thermal stress through a heating system placed in contact with the sheath.

Once the heating is stopped, thermographic images are analysed to identify areas containing filling voids—whether cement grout or petroleum wax—providing a reliable, non‑destructive assessment of sheath integrity.​

Recognition window in a HDPE sheath and video endoscope examination

Visual examination of the injection quality and condition of the cable

Diagnosing external prestressing systems—protected by cement grout or flexible products—may require creating inspection windows through the HDPE sheath to access the cables and their protective material. This allows engineers to visually examine the tendons, perform tests or measurements, and take samples for laboratory analysis.

If a void is detected, a complementary video endoscopy can be carried out to evaluate the extent of the void and assess the condition of the cable beyond the inspection opening.​

In-Tense​

Tension measurement using the crossbow method

The crossbow method is based on the principle that a more highly tensioned reinforcement requires a greater force (F) to produce a given lateral deflection (w).

The residual tension in the prestressing reinforcement is determined by comparing the on‑site measurement curve w = f(F) with a calibration curve specific to the reinforcement type, previously established in laboratory conditions.​

Tension measurement using the vibration method

The vibration frequency of a cable is directly linked to its level of tension. This method records the natural frequencies of the cable and uses the fundamental frequency to estimate its tension, treating the cable as a vibrating string.

EverSense® Acoustics​

Detection of wire breaks using the acoustic method

When an individual wire or strand breaks, it generates a shock wave that propagates through the prestressing cable and the surrounding concrete. Acoustic monitoring captures this wave using a network of sensors placed along the cable and on the structure, typically near anchors or deviation points.

This method makes it possible to detect and locate a loss of cross‑section corresponding to a broken wire, providing early warning of structural deterioration and supporting safe management of prestressed systems.​

Extendo​

Detection of wire breaks using a mechanical method

In externally prestressed cables injected with cement grout, breaks in individual wires or strands cause a redistribution of elongation along the damaged tendon. The Extendo monitoring system measures these micro‑deformations by placing discrete sensors on selected cable branches, allowing engineers to identify and quantify tension loss and detect potential breaks.​

We offer a comprehensive range of expertise to support you in managing and securing your structures with external prestressing

In-depth analysis of the construction file

Preliminary risk analysis and definition of a tailor-made investigation programme

Detailed inspection of external prestressing

Identify leaks in HDPE pipes. Map faults. Perform an immersive inspection of the interior of box girder bridges

Testing

Characterisation of injection quality, assessment of cable condition, measurement of residual voltage

Safety engineering

Model the impact of a cable break on the structure and strapping design

Cable replacement engineering

damaged by corrosion

Instrumentation for monitoring cable ageing