Post tensioning is actually a technique for reinforcing concrete. Post-tensioning tendons is Post Tension Anchor inside plastic ducts or sleeves, are positioned in the forms ahead of the concrete is put.” Post tension cables essentially permit us to safely build large concrete structures. They permit larger spans, thinner slabs and greater distances between support commons. Post tensioning is utilized in bridges and box girder structures globally including on our bridges, off and on ramps. These tendons make it possible to build structures that might not otherwise be possible. Because concrete is not bendable it can crack under loads. Although rebar is utilized to strengthen the concrete to stop cracks from growing the concrete can 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 using a post-tensioned approach. It allows for flexibility of design, faster construction and minimize material costs. In the long run, it may reduce maintenance costs and enable 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 that is unachievable in the event of regular bridges. This technique reinforces or strengthens the concrete or other material with high strength steel bar or strand which is called “tendons”. It significantly cuts down on the building weight and foundation load that is very useful in seismic areas.
Post tension tendons aid in construction of wedge anchor which includes specific geometry requirements such as complex curves and super elevation. Extremely long span bridges could be constructed through the help of post tension tendons. Such architectures functions effectively without disrupting the traffic moving under it as well as reduces 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 are becoming a significant 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 to estimate the remaining lifespan from the affected member.
Infrastructure Preservation Corporation (IPC) has evolved a thorough post tension tendon inspection service named “TendonScan®” which utilizes non destructive testing and evaluation methods that may find corrosion and section loss inside a PT tendon.
What it is? As we have mentioned above 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 system includes a device 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 is likely to separate according to 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 settle this challenge.
How it is used? It is a battery operated robotic system which uses the most recent 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 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 from the tendon condition. The picture of internal part of tendon will be illustrated in 3D color graphics to ensure 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 helps in locating corrosion, voids, bleeding grout, section loss as well as other problems in and out of the tendon. Moreover, it may also help in monitoring the discontinuities during a period of time which will help in deciding that if to repair or replace a post tension tendon.