Post tensioning is actually a technique for strengthening concrete. Post-tensioning tendons is Post Tension Anchorage inside plastic ducts or sleeves, are positioned in the forms prior to the concrete is placed.” Post tension cables ultimately allow us to safely build large concrete constructions. 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, on / off ramps. These tendons have the ability to build structures that might not be possible. Because concrete is not flexible it may crack under loads. Although rebar can be used to strengthen the concrete to avoid cracks from growing the concrete can 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 numerous benefits which can be gained by using a post-tensioned approach. It enables flexibility of design, faster construction and lower material costs. Over the long term, it may reduce maintenance costs and permit 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 can be used that is difficult in case of regular bridges. This technique reinforces or strengthens the concrete or other material rich in strength steel bar or strand which is called “tendons”. It significantly reduces the building weight and foundation load that is very beneficial in seismic areas.
Post tension tendons help in construction of dead-end anchorage which has specific geometry requirements including complex curves and super elevation. Extremely long span bridges may be constructed through the help of post tension tendons. Such architectures functions effectively without disrupting the traffic moving under it and in addition decreases the impact on environment significantly.
Post tension tendons are created from prestressing strand, anchorage, ducts, and grout and corrosion protection materials. As this technology is completely new therefore you will find no inspection systems for tendon components. Recent cases of corrosion of post tension tendons in complex bridges have become 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 also to estimate the rest of the lifespan in the affected member.
Infrastructure Preservation Corporation (IPC) has developed a thorough post tension tendon inspection service named “TendonScan®” which utilizes non destructive testing and evaluation methods that can find corrosion and section loss in a PT tendon.
What it is? Since we have mentioned previously that it is an extensive tendon scanning system which works on non destructive testing principals to find out voids, water intrusion and bleeding grout in external tendons. This technique 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 stop corrosion. But during grouting process, the grout is likely 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 prone to corrosion. Complex bridge inspection is incomplete without tendon testing therefore we now have developed this TendonScan system to resolve this challenge.
The actual way it can be used? It really is a battery operated robotic system that uses the most recent in non destructive testing and modern technology. This technique couples itself using the tendon and travel along it to carry out a MRI like inspection of smtzmh material within 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 information is transferred to control station for real time assessment in the tendon condition. The picture of internal portion of tendon will be illustrated in 3D color graphics in order that any discontinuity like water intrusion, void or bleeding grout can be identified and quantified easily.
What problem does it solve? This barrel and wedge anchor works well for locating corrosion, voids, bleeding grout, section loss as well as other problems in and out of the tendon. Moreover, it can also help in monitoring the discontinuities over a duration of time which will help in deciding that when to repair or replace a post tension tendon.