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 placed.” Post tension cables in effect permit us to safely build large concrete structures. They permit larger spans, thinner slabs and greater distances between support commons. Post tensioning is utilized in bridges and box girder structures worldwide including on our bridges, on and off ramps. These tendons have the ability to construct structures which may not otherwise be feasible. Because concrete is not flexible it may crack under loads. Although rebar is utilized to strengthen the concrete to avoid cracks from growing the concrete can certainly 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 lots of benefits that are gained using a post-tensioned approach. It provides for flexibility of design, faster construction and reduce material costs. Over the long term, 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 used which is not possible in case of regular bridges. This technique reinforces or strengthens the concrete or any other material with high strength steel bar or strand which is known as “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 wedge anchor which includes specific geometry requirements including complex curves and super elevation. Extremely long span bridges may be constructed with the aid of post tension tendons. Such architectures functions effectively without disrupting the traffic moving under it as well as cuts down on the impact on environment significantly.
Post tension tendons are created from prestressing strand, anchorage, ducts, and grout and corrosion protection materials. Because 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 become a substantial problem.
After getting details about tendon corrosion, department of transportation has inspected their post tension structure inventory to gauge and quantify the rate of tendon corrosion and also to estimate the rest of the lifespan of 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 will find corrosion and section loss inside a PT tendon.
What exactly it is? Since we have stated earlier that it is an extensive tendon scanning system which works on non destructive testing principals to find out voids, water intrusion and bleeding grout in external tendons. This method includes a device 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 depending 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 vunerable to corrosion. Complex bridge inspection is incomplete without tendon testing therefore we have now developed this TendonScan system to settle this problem.
How it can be used? This is a battery operated robotic system that uses the latest in non destructive testing and modern technology. This system couples itself using the tendon and travel along it to perform a MRI like inspection of smtzmh material within 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 information is moved to control station for real time assessment of the tendon condition. The image of internal part 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 can it solve? This barrel and wedge anchor helps with locating corrosion, voids, bleeding grout, section loss as well as 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 if to correct or replace a post tension tendon.