Post tensioning is a way of reinforcing concrete. Post-tensioning tendons is Post Tension Anchor inside plastic ducts or sleeves, are situated in the forms before the concrete is put.” Post tension cables essentially allow us to safely build large concrete structures. They allow larger spans, thinner slabs and greater distances between support commons. Post tensioning is used in bridges and box girder structures around the world such as on our bridges, on / off ramps. These tendons make it possible to build structures that might not be possible. Because concrete is not bendable it can crack under loads. Although rebar is used to strengthen the concrete to stop cracks from growing the concrete can certainly still sag under increased loads. PT or post tension tendons are load bearing and can stand large increases in loads bearing up the concrete.
There are lots of benefits which can be gained simply by using a post-tensioned approach. It provides for flexibility of design, faster construction and lower material costs. Over the long term, it may reduce maintenance costs and allow for increased loads as time passes.
Bridges that utilize post tension tendons can contain long and clear spans, have few beams and slender members and thinner slabs may be used which is unachievable in the case of regular bridges. This process reinforces or strengthens the concrete or other material rich in strength steel bar or strand which is known as “tendons”. It significantly reduces the building weight and foundation load which can be very helpful in seismic areas.
Post tension tendons help in construction of dead-end anchorage which includes specific geometry requirements like complex curves and super elevation. Extremely long span bridges can be constructed through the help of post tension tendons. Such architectures functions effectively without disrupting the traffic moving under it and in addition cuts down on 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 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 information regarding tendon corrosion, department of transportation has inspected their post tension structure inventory to assess and quantify the speed of tendon corrosion as well as estimate the remaining lifespan of the affected member.
Infrastructure Preservation Corporation (IPC) has created a thorough 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 stated earlier 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 includes a system to detect section loss inside the tendon.
Why was it developed? During construction of complex bridges, tendons are filled in grout to avoid corrosion. But during grouting process, the grout has a tendency to separate according to 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 settle this issue.
The way it is used? This is a battery operated robotic system which uses the newest in non destructive testing and modern technology. This system couples itself with all 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 combined 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 of the tendon condition. The photo of internal section 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 barrel and wedge anchor helps with locating corrosion, voids, bleeding grout, section loss along with other problems outside and inside the tendon. Moreover, it may also help in monitoring the discontinuities over a duration of time that helps in deciding that when to correct or replace a post tension tendon.