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 placed.” Post tension cables in effect permit 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 around the world including on our bridges, on / off ramps. These tendons make it possible to develop structures which may not be possible. Because concrete is not flexible 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 will stand large increases in loads bearing up the concrete.
There are many benefits which can be gained using a post-tensioned approach. It allows for flexibility of design, faster construction and lower material costs. Over time, it could reduce maintenance costs and enable for increased loads with time.
Bridges that utilize post tension tendons can contain long and clear spans, have few beams and slender members and thinner slabs can be utilized that is difficult in the event of regular bridges. This technique reinforces or strengthens the concrete or other material with higher 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 anchorage grip which includes 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 new therefore you will find no inspection systems for tendon components. Recent cases of corrosion of post tension tendons in complex bridges have become a substantial problem.
After getting information regarding tendon corrosion, department of transportation has inspected their post tension structure inventory to evaluate and quantify the pace of tendon corrosion and to estimate the rest of the lifespan from the affected member.
Infrastructure Preservation Corporation (IPC) has created a thorough 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? While we have mentioned above that it must be 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 also includes a product to detect section loss in 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 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 solve this issue.
How it is used? This is a battery operated robotic system that utilizes the newest in non destructive testing and modern technology. This method 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 combined with the sensor. The sensor works through wireless connectivity to send out the collected data. The information is moved to control station for real-time assessment from the tendon condition. The photo of internal part of tendon will then be illustrated in 3D color graphics to ensure that any discontinuity like water intrusion, void or bleeding grout can be identified and quantified easily.
What problem can it solve? This slab steel anchor helps in locating corrosion, voids, bleeding grout, section loss as well as other problems outside and inside the tendon. Moreover, it can also help in monitoring the discontinuities over a duration of time which will help in deciding that when to fix or replace a post tension tendon.