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 ahead of the concrete is placed.” Post tension cables essentially let us safely build large concrete structures. They allow larger spans, thinner slabs and greater distances between support commons. Post tensioning is utilized in bridges and box girder structures globally such as on our bridges, off and on ramps. These tendons make it possible to develop structures that might not be possible. Because concrete is not flexible it may crack under loads. Although rebar can be used to strengthen the concrete to stop cracks from growing the concrete can still sag under increased loads. PT or post tension tendons are load bearing and can stand large increases in loads bearing up the concrete.
There are lots of benefits which are gained by using a post-tensioned approach. It enables flexibility of design, faster construction and reduce material costs. Over time, it can reduce maintenance costs and allow for increased loads as time passes.
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 that is unachievable in the event of regular bridges. This process reinforces or strengthens the concrete or other material with high strength steel bar or strand which is known as “tendons”. It significantly cuts down on the building weight and foundation load that is very useful in seismic areas.
Post tension tendons aid in construction of post tension anchorage which has specific geometry requirements such as 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 and in addition reduces the influence on environment significantly.
Post tension tendons are created from prestressing strand, anchorage, ducts, and grout and corrosion protection materials. Since this technology is new therefore you will 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.
After getting information about 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 of the affected member.
Infrastructure Preservation Corporation (IPC) has evolved an extensive 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? Since we have mentioned above 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 system comes with a product to detect section loss inside the tendon.
Why was it developed? During construction of complex bridges, tendons are completed grout to avoid corrosion. But during grouting process, the grout has a tendency to separate based 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 prone to corrosion. Complex bridge inspection is incomplete without tendon testing therefore we have now developed this TendonScan system to settle this challenge.
How it is used? It really is a battery operated robotic system that uses the newest in non destructive testing and modern technology. This method couples itself with all the tendon and travel along it to perform a MRI like inspection of smtzmh material inside it. The inspector stands on the mobile control unit which travels along 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 of the tendon condition. The picture of internal section of tendon will then be illustrated in 3D color graphics in order that any discontinuity like water intrusion, void or bleeding grout may be identified and quantified easily.
What problem does it solve? This pre-stressing anchor helps in locating corrosion, voids, bleeding grout, section loss along with other problems outside and inside the tendon. Moreover, it can also help in monitoring the discontinuities over a period of time which helps in deciding that when to repair or replace a post tension tendon.