Post tensioning is a technique for strengthening concrete. Post-tensioning tendons is Barrel And Wedges inside plastic ducts or sleeves, are positioned in the forms before the concrete is placed.” Post tension cables essentially allow us to safely build large concrete constructions. They permit larger spans, thinner slabs and greater distances between support commons. Post tensioning is used in bridges and box girder structures worldwide such as on our bridges, on and off ramps. These tendons have the ability to construct structures that may not be feasible. 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 certainly 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 many 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 could 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 can be used which is difficult in the case of regular bridges. This technique reinforces or strengthens the concrete or any other material rich in strength steel bar or strand which is called “tendons”. It significantly cuts down on the building weight and foundation load that is very useful in seismic areas.
Post tension tendons help in construction of wedge anchor that has specific geometry requirements like 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 reduces the influence on environment significantly.
Post tension tendons are created from prestressing strand, anchorage, ducts, and grout and corrosion protection materials. Because this technology is new therefore you can find no inspection systems for tendon components. Recent cases of corrosion of post tension tendons in complex bridges are becoming a significant problem.
After getting information about tendon corrosion, department of transportation has inspected their post tension structure inventory to assess and quantify the rate of tendon corrosion and to estimate the rest of the lifespan of the affected member.
Infrastructure Preservation Corporation (IPC) has evolved a thorough post tension tendon inspection service named “TendonScan®” which utilizes non destructive testing and evaluation methods that can find corrosion and section loss within a PT tendon.
What it is? Since we have stated earlier that it is an extensive tendon scanning system which works on non destructive testing principals to learn voids, water intrusion and bleeding grout in external tendons. This system comes with 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 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 vunerable to corrosion. Complex bridge inspection is incomplete without tendon testing therefore we now have developed this TendonScan system to solve this issue.
The way it is utilized? 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 perform a MRI like inspection of smtzmh material inside it. The inspector stands on the mobile control unit which travels combined with the sensor. The sensor works through wireless connectivity to transmit the collected data. The information is transferred to control station for real time assessment of the tendon condition. The image of internal portion of tendon is then illustrated in 3D color graphics so that any discontinuity like water intrusion, void or bleeding grout could be identified and quantified easily.
What problem will it solve? This post stressed anchor helps with locating corrosion, voids, bleeding grout, section loss along with other problems inside and outside the tendon. Moreover, it may also help in monitoring the discontinuities over a period of time which helps in deciding that whenever to correct or replace a post tension tendon.