External Prestressing

External prestressing cables are widely used in new construction as well as in the strengthening of existing structures. Because they play a critical role in overall structural performance, these systems must be regularly monitored and inspected to ensure long‑term safety and reliability.

Sixense offers a comprehensive portfolio of solutions for evaluating the condition of external prestressing cables, measuring their residual tension, and detecting breaks in individual wires or strands. Our tools and methods are designed to deliver accurate, actionable insights for even the most complex structures.

Our specialists can support you in designing and implementing a customized inspection program tailored to your external prestressing systems. This approach helps you identify hidden defects early, maintain structural integrity, and manage your externally prestressed assets with confidence.

Our techniques and expertise in external prestressing

Escan

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

Escan is a specialized diagnostic technology developed in partnership with UGE (Université Gustave Eiffel) to assess the condition of external prestressing sheaths. The device uses a capacitive probe made of two electrodes forming a capacitor, whose capacitance varies based on the dielectric properties of the materials inside the HDPE conduit.

The probe fully surrounds the sheath and is moved along the cable, allowing engineers to identify injection defects, voids, or the presence of white paste with precision. This non‑destructive method provides a fast and reliable way to detect anomalies in external prestressing ducts.

Uscan

Detection of wire breaks in the anchorage zone using ultrasonic reflectometry

Uscan uses ultrasonic reflectometry to detect wire breaks in the anchorage zone of external prestressing systems. An ultrasonic transducer generates high‑frequency mechanical waves that propagate along the wire. Any discontinuity—such as a break or localized damage—reflects part of the wave back to the sensor, allowing engineers to identify the defect and approximate its location.

Co‑developed with UGE, Uscan is the only patented technology capable of assessing the condition of prestressing strands directly within the anchorage zone, where visual access is typically impossible.

ITscan – Anchoring

Inspection of anchor caps using active infrared thermography

This patented Sixense method uses active infrared thermography to detect injection defects beneath anchor caps. A custom‑designed inductor applies controlled thermal stress to the cap, and thermographic images are captured immediately after heating stops.

These images reveal voids in cement grout or petroleum wax, as well as the presence of water—critical information for evaluating the integrity of external prestressing anchorages.

ITscan – Sheath

Inspection of sheaths in the main section using active infrared thermography

Similar to the anchorage method, ITscan for sheaths applies active thermal stress along the main length of the external prestressing cable. A heating system is placed in contact with the HDPE sheath, and thermographic images taken after heating highlight areas where grout or wax is missing.

This technique provides a fast, non‑intrusive way to map injection defects along long cable sections.

Recognition Window in an HDPE Sheath & Video Endoscope Examination

Direct visual inspection of injection quality and cable condition

Diagnosing external prestressing systems protected by cement grout or flexible products may require opening inspection windows in the HDPE sheath. This allows engineers to visually examine the cable, assess the protective material, perform tests, or collect samples for laboratory analysis.

If a void is discovered, video endoscopy can be used to explore the duct further, providing detailed insight into the extent of the defect and the condition of the cable beyond the inspection window.

In-Tense

Tension measurement using the crossbow method

The crossbow method measures residual tension in external prestressing reinforcement by determining the force (F) required to laterally deflect the cable by a known distance (w). The on‑site measurement curve is compared with a laboratory calibration curve specific to the reinforcement type.

This technique provides a reliable, repeatable way to quantify remaining tension in prestressing tendons.

Tension Measurement Using the Vibration Method

The natural vibration frequency of a cable is directly related to its tension. This method records the cable’s fundamental frequency and treats the cable as a vibrating string to estimate its tension.

It is a fast, non‑destructive technique well‑suited for external prestressing systems where direct access to the tendon is limited.

EverSense® Acoustics

Detection of wire breaks using the acoustic method

When a wire or strand in an external prestressing cable breaks, it releases a shock wave that travels through the cable and surrounding concrete. EverSense® Acoustics uses a network of sensors placed along the cable and near anchors or deviators to detect this wave.

By analyzing the arrival times at different sensors, engineers can identify and locate the loss of cross‑section corresponding to a broken wire. This real‑time monitoring capability is essential for managing risk in critical structures.

Extendo

Detection of wire breaks using a mechanical method

In externally prestressed cables injected with cement grout, a broken wire or strand causes a redistribution of elongation along the tendon. Extendo detects these changes by measuring micro‑deformations using discrete sensors installed along the cable branches.

This mechanical method provides a reliable way to identify wire breaks in external prestressing systems where other techniques may be difficult to apply.

Comprehensive Expertise for Managing and Securing Your Structures with External Prestressing

In‑depth analysis of construction documentation

We review all available design and construction records to understand the original configuration of your external prestressing system and identify potential areas of concern.

Preliminary risk analysis and tailored investigation planning

Our specialists conduct a structured risk assessment and develop a customized investigation program aligned with your structure’s specific needs.

Detailed inspection of external prestressing

We identify leaks in HDPE ducts, map defects along the cable path, and perform immersive internal inspections of box‑girder bridges to evaluate the condition of external prestressing components.

Testing and diagnostic evaluation

Our testing services include characterization of injection quality, assessment of cable condition, and measurement of residual tension to determine the performance of your external prestressing system.

Safety engineering

We model the structural consequences of a potential cable break and design appropriate strapping or reinforcement strategies to maintain safety and serviceability.

Cable replacement engineering

For cables damaged by corrosion or deterioration, we provide engineering support for safe, efficient replacement and reinstatement of external prestressing capacity.

Instrumentation for monitoring cable aging

We deploy advanced monitoring systems to track long‑term cable behavior, detect early signs of degradation, and support proactive asset management.