Post tensioning is a way of reinforcing concrete. Post-tensioning tendons is Post Tension Anchorage inside plastic ducts or sleeves, are situated in the forms before the concrete is placed.” Post tension cables ultimately let us safely build large concrete constructions. They permit 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 develop structures that might not otherwise be feasible. Because concrete is not bendable it may crack under loads. Although rebar can be used to reinforce the concrete to stop 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 that are gained 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 enable for increased loads with time.
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 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 decreases the building weight and foundation load which is very useful in seismic areas.
Post tension tendons assist in construction of post tension anchorage which has specific geometry requirements like 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 decreases the effect on environment significantly.
Post tension tendons are made from prestressing strand, anchorage, ducts, and grout and corrosion protection materials. Since this technology is totally new therefore you can find no inspection systems for tendon components. Recent cases of corrosion of post tension tendons in complex bridges have grown to be 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 rate of tendon corrosion and also to estimate the remaining lifespan from the affected member.
Infrastructure Preservation Corporation (IPC) has evolved a comprehensive post tension tendon inspection service named “TendonScan®” which utilizes non destructive testing and evaluation methods that may find corrosion and section loss in a PT tendon.
What exactly it is? As we have mentioned above that it is a comprehensive tendon scanning system which works on non destructive testing principals to find out voids, water intrusion and bleeding grout in external tendons. This method also includes a system to detect section loss within the tendon.
Why was it developed? During construction of complex bridges, tendons are filled in grout to prevent 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 susceptible to corrosion. Complex bridge inspection is incomplete without tendon testing therefore we have now developed this TendonScan system to solve this issue.
How it is used? This is a battery operated robotic system that utilizes the latest in non destructive testing and modern technology. This method couples itself using the tendon and travel along it to do a MRI like inspection of smtzmh material inside 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 details are transferred to control station for live assessment of the tendon condition. The picture of internal part 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 does it solve? This slab steel anchor works well for locating corrosion, voids, bleeding grout, section loss and other problems outside and inside the tendon. Moreover, it can also help in monitoring the discontinuities over a duration of time which helps in deciding that whenever to correct or replace a post tension tendon.