Post tensioning is actually a way of reinforcing 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 let us safely build large concrete structures. They enable 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, on and off ramps. These tendons have the ability to construct structures that might not be possible. Because concrete is not bendable it can crack under loads. Although rebar can be used to reinforce the concrete to prevent 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 many benefits which are gained by using a post-tensioned approach. It allows for flexibility of design, faster construction and lower material costs. Over time, it can reduce maintenance costs and permit for increased loads over time.
Bridges that utilize post tension tendons can 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 other material rich in 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 includes specific geometry requirements like complex curves and super elevation. Extremely long span bridges can be constructed with the help of post tension tendons. Such architectures functions effectively without disrupting the traffic moving under it as well as decreases the impact on environment significantly.
Post tension tendons are created from prestressing strand, anchorage, ducts, and grout and corrosion protection materials. As 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 have become an important problem.
Once you have information regarding tendon corrosion, department of transportation has inspected their post tension structure inventory to gauge and quantify the speed of tendon corrosion as well as estimate the other lifespan in the affected member.
Infrastructure Preservation Corporation (IPC) has created an extensive 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? Since we have mentioned previously that it is a thorough tendon scanning system which works on non destructive testing principals to learn voids, water intrusion and bleeding grout in external tendons. This method includes a product to detect section loss within the tendon.
Why was it developed? During construction of complex bridges, tendons are completed grout to stop corrosion. But during grouting process, the grout has a tendency 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 prone to corrosion. Complex bridge inspection is incomplete without tendon testing therefore we now have developed this TendonScan system to resolve this challenge.
How it can be used? It really 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 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 portion of tendon is then illustrated in 3D color graphics so that any discontinuity like water intrusion, void or bleeding grout can be identified and quantified easily.
What problem will it solve? This slab steel 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 which helps in deciding that whenever to repair or replace a post tension tendon.