Post tensioning is actually a technique for reinforcing concrete. Post-tensioning tendons is Post Tension Anchor inside plastic ducts or sleeves, are situated in the forms prior to the concrete is placed.” Post tension cables ultimately let us 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 worldwide such as on our bridges, off and on ramps. These tendons have the ability to construct structures that might not be attainable. Because concrete is not flexible it may crack under loads. Although rebar is utilized to strengthen the concrete to prevent 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 numerous benefits which can be gained simply by using a post-tensioned approach. It provides for flexibility of design, faster construction and reduce material costs. In the long run, it could reduce maintenance costs and allow 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 may be used which is not possible in the case of regular bridges. This process reinforces or strengthens the concrete or some other material with high strength steel bar or strand which is known as “tendons”. It significantly reduces the building weight and foundation load which can be very beneficial in seismic areas.
Post tension tendons assist in construction of dead-end anchorage which includes specific geometry requirements like complex curves and super elevation. Extremely long span bridges could be constructed with the aid of post tension tendons. Such architectures functions effectively without disrupting the traffic moving under it and in addition decreases the influence 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 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 details about tendon corrosion, department of transportation has inspected their post tension structure inventory to assess and quantify the rate of tendon corrosion as well as estimate the rest of the lifespan from 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 inside a PT tendon.
What exactly it is? As we have stated earlier that it must be a comprehensive tendon scanning system which works on non destructive testing principals to discover voids, water intrusion and bleeding grout in external tendons. This technique comes with a system 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 has a tendency to separate depending 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 vunerable to corrosion. Complex bridge inspection is incomplete without tendon testing therefore we have now developed this TendonScan system to solve this challenge.
How it is utilized? It is a battery operated robotic system that uses the most recent in non destructive testing and modern technology. This method 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 together with the sensor. The sensor works through wireless connectivity to send out the collected data. The information is transferred to control station for real time assessment in the tendon condition. The image of internal section of tendon will then 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 will it solve? This barrel and wedge anchor works well for locating corrosion, voids, bleeding grout, section loss as well as other problems inside and outside the tendon. Moreover, it can also help in monitoring the discontinuities over a duration of time which will help in deciding that when to fix or replace a post tension tendon.