What is a post tension tendon?

“Post tensioning is a technique for reinforcing concrete. Post-tensioning tendons, which are pre-stressing steel cables inside plastic ducts or sleeves, are positioned in the forms before the concrete is placed.” Post tension cables in effect allow us to safely build large concrete structures. They allow larger spans, thinner slabs and greater distances between support commons. Post tensioning is used in bridges and box girder structures worldwide including on our bridges, on and off ramps.  Post tensioning makes it possible to build structures that might not otherwise be possible. Because concrete is not flexible it can crack under loads.  Although rebar is used to reinforce the concrete to prevent cracks from growing the concrete can still sag under increased loads. PT or post tension cables are load bearing and can stand large increases in loads bearing up the concrete.

There are many benefits that are gained by using a post-tensioned approach.  It allows for flexibility of design, faster construction and lower material costs. Over the long term, it can reduce maintenance costs and allow for increased loads over time.

Bridges that utilize post tension tendons are able to contain long and clear spans, have few beams and slender members and thinner slabs can be used which is not possible in case of regular bridges. This method reinforces or strengthens the concrete or other material with high strength steel bar or strand which is known as “tendons”. It significantly reduces the building weight and foundation load which is very useful in seismic areas.

Post tension tendons help in construction of complex bridges which has specific geometry requirements such as complex curves and super elevation. Extremely long span bridges can be constructed with the help of post tension tendons. Such architectures functions effectively without disrupting the traffic moving under it and also reduces the impact on environment significantly.

Post tension tendons are made of prestressing strand, anchorage, ducts, and grout and corrosion protection materials. Since this technology is new therefore there are no inspection systems for tendon components. Recent cases of corrosion of post tension tendons in complex bridges have become a significant problem.

After getting information about tendon corrosion, department of transportation has inspected their post tension structure inventory to assess and quantify the rate of tendon corrosion and to estimate the remaining lifespan of the affected member.

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

What it is?

As we have mentioned above that it is a comprehensive tendon scanning system which works on non destructive testing principals to find out voids, water intrusion and bleeding grout in external tendons. This system also includes a device to detect section loss within the tendon.

Why was it developed?

During construction of complex bridges, tendons are filled in grout to prevent corrosion. But during grouting process, the grout tends to separate depending on grout’s quality, admixtures, pumping equipment and procedures. This separation result into low pH grout at tendon points and anchorage which made these locations susceptible to corrosion.

Complex bridge inspection is incomplete without tendon testing therefore we have developed this TendonScan system to resolve this problem.

How it is used?

It is a battery operated robotic system that uses the latest in non destructive testing and modern technology. This system couples itself with the tendon and travel along it to perform a MRI like inspection of the material inside it. The inspector stands on the mobile control unit which travels along with the sensor. The sensor works through wireless connectivity to transmit the collected data. The information is transferred to control station for real time assessment of the tendon condition. The image of internal section of tendon is then illustrated in 3D color graphics so that any discontinuity like water intrusion, void or bleeding grout can be identified and quantified easily.

What problem does it solve?

This tendon assessment system helps in locating corrosion, voids, bleeding grout, section loss and other problems inside and outside the tendon. Moreover, it also helps in monitoring the discontinuities over a period of time which helps in deciding that when to repair or replace a post tension tendon. 

To know more about our products and services, you can visit our website https://www.infrastructurepc.com/ or contact us at info@infrastructurepc.com.