External prestressing cables are used in new constructions and as a reinforcement technique for existing structures. They play an essential role in structural strength and must be periodically monitored and inspected.
Sixense has a unique portfolio of solutions for assessing the condition of external prestressing cables, measuring their residual tension, and identifying breaks in wires or strands.
Our specialists can advise you on designing and implementing a bespoke inspection programme for your cables, helping you to detect hidden defects and ensure the safe management of your externally prestressed structures.
Escan technology was developed in partnership with UGE (Université Gustave Eiffel). The measuring device is a capacitive probe consisting of two electrodes forming a capacitor, whose capacity depends on the dielectric characteristics of the materials inside the HDPE conduit being inspected. The auscultation device, which completely surrounds the sheath, is moved along the cable to highlight any injection anomalies.
The ultrasonic reflectometry technique is based on the propagation of very high frequency mechanical waves generated by an ultrasonic transducer pressed against the end of the wire being tested. This guided wave makes it possible to identify damage to the wire and the approximate location of the discontinuity from the point of emission. The patented Uscan technology, co-developed with UGE, is the only technology that can assess the condition of prestressing strands in the anchorage zone.
This method, patented by Sixense, detects injection defects under active thermal stress using a custom-made inductor applied in contact with the anchor cap. An examination of the thermographic images obtained immediately after the thermal stress is stopped allows the location of voids (cement grout or petroleum wax) and the presence of water, if any.
As with anchor covers, this method detects injection defects in the main section of cables under active thermal stress using a heating system applied in contact with the sheath. An examination of the thermographic images obtained immediately after the thermal stress is stopped allows the areas of filling voids (cement grout or petroleum wax) to be located.
Diagnosis of external prestressing, protected by cement grout or a flexible product, may require the opening of windows through the HDPE sheath to reach the prestressing cables and their protective product in order to examine them, carry out tests or measurements, or take samples for laboratory analysis and testing. In the event of a void, an additional video endoscopy examination may be carried out to observe the extent of the void and the condition of the cable beyond the inspection window.
The crossbow method is based on the fact that the more a reinforcement is tensioned, the greater the force (F) required to deflect it from its path by a distance (w) will be greater.
The residual tension in the prestressing reinforcement is obtained by comparing the measurement curve w=f(F) obtained on site with a calibration curve specific to each type of reinforcement tested, established in the laboratory.
The vibration frequency of a cable is related to its tension. The method consists of recording the natural frequencies of the cable being tested and estimating its tension by using the value of the fundamental frequency, assimilating the vibration of the cable to that of a vibrating string.
When an elementary wire or strand breaks, it emits a shock wave that propagates through the cable and the surrounding concrete. Acoustic monitoring consists of detecting this wave using a network of sensors positioned along the cable and on the structure, near the anchors or deflectors. A loss of cross-section corresponding to a lost wire can be detected and located.
On externally prestressed cables injected with cement grout, breaks in individual wires or strands result in a redistribution of elongation along the damaged cable. The Extendo monitoring device is based on the measurement of micro-deformations in the cable by positioning discrete sensors on the branches to be monitored.