Post tensioning is a technique for strengthening concrete. Post-tensioning tendons is Post Tension Anchor inside plastic ducts or sleeves, are situated in the forms ahead of the concrete is placed.” Post tension cables essentially let us safely build large concrete structures. They permit larger spans, thinner slabs and greater distances between support commons. Post tensioning is used in bridges and box girder structures globally such as on our bridges, on and off ramps. These tendons make it possible to develop structures that may not be possible. Because concrete is not bendable it may crack under loads. Although rebar can be used to reinforce the concrete to prevent cracks from growing the concrete can certainly still sag under increased loads. PT or post tension tendons are load bearing and will stand large increases in loads bearing up the concrete.
There are many benefits which are gained by using a post-tensioned approach. It provides for flexibility of design, faster construction and minimize material costs. In the long run, it may reduce maintenance costs and enable for increased loads with time.
Bridges that utilize post tension tendons are able to contain long and clear spans, have few beams and slender members and thinner slabs may be used which can be unachievable in the event of regular bridges. This method reinforces or strengthens the concrete or some other material rich in strength steel bar or strand which is known as “tendons”. It significantly cuts down on the building weight and foundation load which is very useful in seismic areas.
Post tension tendons assist in construction of dead-end anchorage which includes specific geometry requirements such as complex curves and super elevation. Extremely long span bridges can be constructed with the aid of post tension tendons. Such architectures functions effectively without disrupting the traffic moving under it and also decreases the effect on environment significantly.
Post tension tendons are created from prestressing strand, anchorage, ducts, and grout and corrosion protection materials. Since this technology is completely new therefore there are no inspection systems for tendon components. Recent cases of corrosion of post tension tendons in complex bridges have become an important problem.
Once you have information regarding 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 rest of the lifespan in the affected member.
Infrastructure Preservation Corporation (IPC) has created an extensive post tension tendon inspection service named “TendonScan®” which utilizes non destructive testing and evaluation methods that will find corrosion and section loss within a PT tendon.
What it is? While we have mentioned previously that it is a thorough tendon scanning system which works on non destructive testing principals to discover voids, water intrusion and bleeding grout in external tendons. This method includes a system to detect section loss in the tendon.
Why was it developed? During construction of complex bridges, tendons are filled in grout to stop corrosion. But during grouting process, the grout tends to separate based on grout’s quality, admixtures, pumping equipment and operations. 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 now have developed this TendonScan system to settle this issue.
The way it can be used? This is a battery operated robotic system which uses the latest in non destructive testing and modern technology. This technique couples itself with the tendon and travel along it to perform a MRI like inspection of smtzmh material inside it. The inspector stands on the mobile control unit which travels together with the sensor. The sensor works through wireless connectivity to deliver the collected data. The details are moved to control station for real time assessment in the tendon condition. The image of internal part of tendon will then be illustrated in 3D color graphics in order that any discontinuity like water intrusion, void or bleeding grout could be identified and quantified easily.
What problem does it solve? This post stressed anchor works well for locating corrosion, voids, bleeding grout, section loss as well as other problems inside and outside the tendon. Moreover, it may also help in monitoring the discontinuities over a period of time that helps in deciding that when to fix or replace a post tension tendon.