Post tensioning is a way of strengthening concrete. Post-tensioning tendons is Post Tension Anchor inside plastic ducts or sleeves, are positioned in the forms ahead of the concrete is placed.” Post tension cables ultimately permit 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 worldwide including on our bridges, on / off ramps. These tendons have the ability to develop structures which may not otherwise 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 may stand large increases in loads bearing up the concrete.
There are many benefits that are gained simply by using a post-tensioned approach. It provides for flexibility of design, faster construction and minimize material costs. Over time, it may reduce maintenance costs and allow for increased loads as time passes.
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 can be unachievable in case of regular bridges. This technique reinforces or strengthens the concrete or some other material with high strength steel bar or strand which is called “tendons”. It significantly decreases the building weight and foundation load which can be very helpful in seismic areas.
Post tension tendons assist in construction of dead-end anchorage which has specific geometry requirements like complex curves and super elevation. Extremely long span bridges could be constructed with the help of post tension tendons. Such architectures functions effectively without disrupting the traffic moving under it as well as cuts down on the effect on environment significantly.
Post tension tendons are made of prestressing strand, anchorage, ducts, and grout and corrosion protection materials. Since this technology is totally new therefore you will find 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 details about tendon corrosion, department of transportation has inspected their post tension structure inventory to gauge and quantify the rate of tendon corrosion and also to estimate the rest of the lifespan from the affected member.
Infrastructure Preservation Corporation (IPC) has developed 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 stated earlier that it must be an extensive tendon scanning system which works on non destructive testing principals to discover voids, water intrusion and bleeding grout in external tendons. This system includes a device to detect section loss inside the tendon.
Why was it developed? During construction of complex bridges, tendons are completed grout to avoid corrosion. But during grouting process, the grout has a tendency to separate depending 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 vunerable to corrosion. Complex bridge inspection is incomplete without tendon testing therefore we have now developed this TendonScan system to resolve this issue.
How it is used? It is a battery operated robotic system that uses the latest in non destructive testing and modern technology. This technique couples itself with all the tendon and travel along it to do a MRI like inspection of smtzmh material within 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 from the tendon condition. The photo of internal section of tendon is then illustrated in 3D color graphics so that any discontinuity like water intrusion, void or bleeding grout may be identified and quantified easily.
What problem does it solve? This pre-stressing anchor works well for locating corrosion, voids, bleeding grout, section loss as well as other problems outside and inside the tendon. Moreover, it also helps in monitoring the discontinuities over a duration of time which will help in deciding that if to correct or replace a post tension tendon.