Post tensioning is a way of reinforcing concrete. Post-tensioning tendons is Post Tension Anchorage inside plastic ducts or sleeves, are positioned in the forms before the concrete is put.” Post tension cables ultimately allow us to safely build large concrete constructions. They permit larger spans, thinner slabs and greater distances between support commons. Post tensioning is utilized in bridges and box girder structures worldwide such as on our bridges, off and on ramps. These tendons make it possible to develop structures that might not be attainable. Because concrete is not flexible it can crack under loads. Although rebar is used to reinforce the concrete to avoid 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 lots of benefits which can be gained simply by using a post-tensioned approach. It provides for flexibility of design, faster construction and minimize material costs. In the long run, it may reduce maintenance costs and permit for increased loads over time.
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 utilized 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 cuts down on the building weight and foundation load which can be very useful in seismic areas.
Post tension tendons aid in construction of post tension anchorage that has specific geometry requirements such as 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 also decreases the impact 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 there are 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 about tendon corrosion, department of transportation has inspected their post tension structure inventory to assess and quantify the pace of tendon corrosion and to estimate the other lifespan from the affected member.
Infrastructure Preservation Corporation (IPC) has developed an extensive post tension tendon inspection service named “TendonScan®” which utilizes non destructive testing and evaluation methods that can find corrosion and section loss in a PT tendon.
What exactly it is? Since we have mentioned above 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 technique includes a product 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 tends 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 susceptible to corrosion. Complex bridge inspection is incomplete without tendon testing therefore we have now developed this TendonScan system to solve this issue.
The way it is used? This is a battery operated robotic system that utilizes the newest in non destructive testing and modern technology. This technique couples itself with the tendon and travel along it to carry out 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 from the tendon condition. The photo of internal portion of tendon will be illustrated in 3D color graphics so that any discontinuity like water intrusion, void or bleeding grout may be identified and quantified easily.
What problem does it solve? This post stressed anchor works well for locating corrosion, voids, bleeding grout, section loss along with other problems in and out of the tendon. Moreover, it may also help in monitoring the discontinuities over a period of time that helps in deciding that if to correct or replace a post tension tendon.