Post tensioning is actually a way of strengthening concrete. Post-tensioning tendons is Post Tension Anchorage inside plastic ducts or sleeves, are positioned in the forms prior to the concrete is put.” Post tension cables in effect permit us to safely build large concrete structures. They allow larger spans, thinner slabs and greater distances between support commons. Post tensioning can be used in bridges and box girder structures globally such as on our bridges, off and on ramps. These tendons make it possible to build structures that might not be feasible. Because concrete is not flexible it may crack under loads. Although rebar is used to strengthen 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 may stand large increases in loads bearing up the concrete.
There are lots of benefits that are gained by using a post-tensioned approach. It allows for flexibility of design, faster construction and reduce material costs. Over the long term, it could reduce maintenance costs and enable for increased loads over time.
Bridges that utilize post tension tendons have the ability to contain long and clear spans, have few beams and slender members and thinner slabs can be used which is not possible in the event of regular bridges. This process reinforces or strengthens the concrete or some other material rich in strength steel bar or strand which is known as “tendons”. It significantly decreases the building weight and foundation load which is very helpful in seismic areas.
Post tension tendons aid in construction of anchorage grip which has 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 cuts down on the influence on environment significantly.
Post tension tendons are created from prestressing strand, anchorage, ducts, and grout and corrosion protection materials. Because this technology is new therefore there are no inspection systems for tendon components. Recent cases of corrosion of post tension tendons in complex bridges are becoming a substantial problem.
Once you have information about tendon corrosion, department of transportation has inspected their post tension structure inventory to assess and quantify the speed of tendon corrosion and to estimate the other lifespan from the affected member.
Infrastructure Preservation Corporation (IPC) has evolved 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 exactly it is? Since we have mentioned previously that it is a thorough tendon scanning system which works on non destructive testing principals to find out voids, water intrusion and bleeding grout in external tendons. This system comes with a device to detect section loss within the tendon.
Why was it developed? During construction of complex bridges, tendons are completed grout to avoid corrosion. But during grouting process, the grout tends to separate based 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 prone to corrosion. Complex bridge inspection is incomplete without tendon testing therefore we have now developed this TendonScan system to solve this issue.
How it is used? This is a battery operated robotic system that utilizes the most recent in non destructive testing and modern technology. This method 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 along with the sensor. The sensor works through wireless connectivity to transmit the collected data. The details are transferred to control station for real time assessment of the tendon condition. The picture 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 may be identified and quantified easily.
What problem can it solve? This pre-stressing anchor works well for locating corrosion, voids, bleeding grout, section loss as well as other problems inside and outside the tendon. Moreover, it also helps in monitoring the discontinuities over a duration of time which will help in deciding that if to fix or replace a post tension tendon.