Introduction to Post Tension Tendons

Post-tensioning is a technique for reinforcing concrete. Post-tensioned tendons are pre-stressed steel cables within conduits or plastic sleeves, which are placed in forms before concrete is placed.” Post-tensioned cables do indeed allow us to safely build large concrete structures. greater distances between common supports.Post-tensioning is used in bridge and box girder structures around the world, including our bridges, entrance and exit ramps.These tendons make it possible to build structures that otherwise would not be possible.Because concrete not flexible, can crack under loads. Although rebar is used to reinforce concrete to prevent cracks from growing, concrete can still sag under increased loads. PT or Post Tension Tendons are load bearing and can withstand large increases in the loads supported by the concrete.

There are many benefits to be gained from using a post-tensioning approach. Allows for design flexibility, faster construction, and lower material costs. In the long run, it can reduce maintenance costs and allow for higher loads over time.

Bridges using post-tensioning tendons can contain long, clear spans, have few beams and thin members, and thinner slabs can be used, which is not possible for regular bridges. This method reinforces or strengthens concrete or other material with a high-strength steel bar or wire known as “tendons.” Significantly reduces the weight of the building and the load of the foundation, which is very useful in seismic areas.

Post-tensioning tendons aid in the construction of complex bridges that have specific geometric requirements, such as complex curves and superelevation. Extremely long-span bridges can be built with the aid of post-tensioning tendons. Such architectures work effectively without disrupting the traffic moving under them and also significantly reduce the impact on the environment.

Post-tensioned tendons are made of pre-stressed strands, anchors, conduit, and grout and corrosion protection materials. Since this technology is new, there are no inspection systems for tendon components. Recent cases of corrosion of post-tensioning tendons in complex bridges have become a significant problem.

After obtaining information on tendon corrosion, the Department of Transportation inspected its inventory of post-tensioned structures to assess and quantify the rate of tendon corrosion and estimate the remaining useful life of the affected member.

Infrastructure Preservation Corporation (IPC) has developed a comprehensive post-tension tendon inspection service called “TendonScan®” that uses non-destructive testing and evaluation methods that can find corrosion and loss of section within a PT tendon.

What it is?

As we mentioned earlier, this is a comprehensive tendon scanning system that works on non-destructive testing principles to discover voids, water intrusion, and bleeding slurry in external tendons. This system also includes a device to detect loss of section within the tendon.

Why was it developed?

During the construction of complex bridges, the tendons are filled with grout to prevent corrosion. But during the grouting process, the grout tends to separate based on grout quality, admixtures, pumping equipment, and procedures. This separation results in a low pH slurry at tendon and anchor points, making these locations susceptible to corrosion.

Inspection of complex bridges is incomplete without testing the tendon, so we have developed this TendonScan system to solve this problem.

How is it used?

It is a battery-operated robotic system that uses the latest in non-destructive testing and modern technology. This system engages with the tendon and travels along it to perform an MRI-like inspection of the material within. The inspector is in the mobile control unit that travels with the sensor. The sensor works using wireless connectivity to transmit the collected data. The information is transferred to the control station for real-time evaluation of the condition of the tendon. The image of the internal section of the tendon is then illustrated in 3D color graphics so that any discontinuities, such as water intrusion, voids, or bleeding grout, can be easily identified and quantified.

What problem does it solve?

This tendon evaluation system helps locate corrosion, voids, bleeding grout, loss of section, and other problems inside and outside the tendon. In addition, it also helps to monitor discontinuities over a period of time, helping to decide when to repair or replace a back tension tendon.