Post Tensioned Tendon inspections

Bridges are valuable transportation assets utilized on daily basis. This makes the maintenance of the bridge more essential and significant. Since they are exposed to weather and temperature changes, they become prone to damages like corrosion, cracks etc. A neglected defect on an infrastructure like a bridge may turn out to be dangerous if not identified and repaired on time.

The construction of the bridge is done with utmost care by setting guidelines for materials and construction procedures by professional engineers and craftment. Long lasting material like concrete and steel are used in bridge construction worldwide. To prevent concrete from cracking and collapsing under a load Post-Tension tendons areused to reinforce the concrete.  With the use of post tensioning bridges can be built with less concrete and better withstand the test of time. The advantages of PT concrete have enabled us to build magnificent structures like hi rise buildings and massive bridges. These tendons just like all infrastructure assets need to be properly inspected and maintained to insure the structures safety.

Why are Post Tension tendon inspections important?

To keep the tendons free from damages like corrosion, they are placed in ducts made of plastic or galvanized steel. After the installation of the components and tensioning of the tendons, the ducts are filled with cement grout. However, because of the grout, the ducts are not completely sealed. This makes the ducts prone to crack and corrosion which allows the moisture and air to reach the steel tendons and cause corrosion. Metal loss through this process may make the whole infrastructure weak if not repaired on time. Therefore, the post-tension tendon inspection is of utmost necessity to locate such damages and fix them before any mishap.

What happens during the Post tension tendon inspection?

Till now post tension tendon inspections consisted of a visual inspection with an inspector walking under the bridge with a flashlight looking at the tendon.  In some cases a process called sounding is used. This is where the inspector hits the tendon with a hammer and listens for changes in the sound. Both of these inspection types are subjective and will vary from inspector to inspector. A company in Florida Infrastructure Preservation Corporation “IPC” is changing all of that. A robotic engineering and bridge inspection company, IPC has developed a robotic magnetic flux leakage device that can in effect peer through the concrete and outer wrapping to inspect the steel for section loss and corrosion. The tendon inspection guarantees quantitative data that allows the bridge owner, department of transportation to properly allocate their assets in order to conduct repairs according to importance. The condition assessment report will then be provided that allows repairs to be made to the right area extending the service life of the structure and keeping the public safe.

Infrastructure Preservation Corporation (IPC) offers this service within the department of transportation’s current maintenance budget. Whether you require baseline condition assessment, healthy tendon monitoring or locating corrosion, IPC can provide a complete quantitative post tension tendon inspection with detailed quantitative results unmatched in the industry today.

To know more about our services, you can log on to our website http://www.infrastructurepc.com/  or email us at info@infrastructurepc.com. You can also get a free estimate of our services by providing your details. IPC is a professional services bridge inspection and robotic engineering company providing nondestructive testing services at the same rates as current manual inspections. Their goal is to have the industry do away with subjective inspections by using modern technology and techniques to provide real quantitative data to the department of transportation.

Role of post tensioning in construction of efficient infrastructures

With the advancement in science, our world is evolving and so does the infrastructure. The demand of smart infrastructure has increased in recent decades which demand an upgraded quality of concrete so that the structure can support any load beyond its own dead weight. Many structures have collapsed in past because

• The concrete structure couldn’t bear the oversized load e.g. I-5 Skagit River Bridge accident in 2013

• It was structurally too rigid to withstand the damaging factors like strong winds e.g. I-35W Mississippi River Bridge collapse in 2007

• Frequent accidents where vehicles hit the supporting post like boat colliding with the foundation of the bridge e.g. 14th Street Bridge accident in 1982

• Design errors and material used in the construction e.g. Tacoma Narrows Bridge accident in 1940.

• Earthquakes causing damage to the structure e.g. San Francisco – Oakland Bay Bridge collapse in 1989

We have learned from these accidents that if the design and construction quality of any infrastructure is improved then accidents like bridge failures can be prevented. Post tensioning technique which uses prestressed post tensioned tendons to reinforce concrete structures has revolutionized the construction of infrastructures.  it offers many advantages over regular construction technique. Some of the features of post tensioning are following as

• It offers flexibility to the structure means if the structure tend to sag or deflect under the live load then also the concrete structure won’t crack.

• It has lowered down the material and maintenance cost

• It has also reduced the construction time because it allows longer spans in a structure without building supports.

• It increases the tensile strength and load bearing capacity of the structure thus making it durable and long lasting.

• It can also resist the environmental factors e.g. it can withstand stronger winds or earthquakes as it is structurally flexible.

How post tensioning improves the quality of concrete?

Post tension tendons made from high tensile steel, carbon fibre or aramid fibre is placed within or adjacent to concrete volume to provide flexibility to the concrete structure. When extra pressure is applied by the living load, the post tension tendons share the load and prevent cracking in the concrete member.

Once the concrete is stressed along with tendons, it becomes high strength concrete and can withstand tension forces. Post tension tendons and prestressed concrete is widely used in building huge structures like bridges, skyscrapers, dams, silos and tanks, nuclear containment structures and industrial pavement etc. Prestressed concrete with post tension tendons is much better option than the reinforced concrete because of its improved performance which allows reduced structural thickness and longer span which is essential for building complex structures.

What is the constraint while using post tension tendon in concrete structures?

The biggest advantage of post tensioning is lack of cracking and ability to span large spaces without any support. Post tension slabs can be placed or stamped just like reinforced concrete slab and the surface can be overlaid or stained. It is important to consider that the post tensioned concrete should not be cut or drilled because once a post tension tendon is cut down, it is difficult to repair or replace.

It is very difficult to find any damage to the post tension tendons from the surface as they are deeply embedded inside the concrete member. Infrastructure Preservation Corporation (IPC) provides the first post tension tendon scanning system which utilizes the Electrical Capacitance Tomography (ECT) to perform a MRI like assessment of the post tension tendons. This system is referred as “TendonScan” and it can provide accurate information about any deterioration or section loss like corrosions, voids, bleeding grout and any other problem caused to the tendons so that the decision makers can take appropriate action for repairs, in budget and on time.

To know more about TendonScan, our other products and services, you can visit our website https://www.infrastructurepc.com/ or contact us at info@infrastructurepc.com.

What is a post tension tendon?

“Post tensioning is a technique for reinforcing concrete. Post-tensioning tendons, which are pre-stressing steel cables inside plastic ducts or sleeves, are positioned in the forms before the concrete is placed.” Post tension cables in effect allow us to safely build large concrete structures. They allow larger spans, thinner slabs and greater distances between support commons. Post tensioning is used in bridges and box girder structures worldwide including on our bridges, on and off ramps.  Post tensioning makes it possible to build structures that might not otherwise be possible. Because concrete is not flexible it can crack under loads.  Although rebar is used to reinforce the concrete to prevent cracks from growing the concrete can still sag under increased loads. PT or post tension cables are load bearing and can stand large increases in loads bearing up the concrete.

There are many benefits that are gained by using a post-tensioned approach.  It allows for flexibility of design, faster construction and lower material costs. Over the long term, it can reduce maintenance costs and allow for increased loads over time.

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 not possible in case of regular bridges. This method reinforces or strengthens the concrete or other material with high strength steel bar or strand which is known as “tendons”. It significantly reduces the building weight and foundation load which is very useful in seismic areas.

Post tension tendons help in construction of complex bridges 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 also reduces the impact on environment significantly.

Post tension tendons are made of prestressing strand, anchorage, ducts, and grout and corrosion protection materials. Since this technology is new therefore there are no inspection systems for tendon components. Recent cases of corrosion of post tension tendons in complex bridges have become 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 remaining lifespan of the affected member.

Infrastructure Preservation Corporation (IPC) has developed a comprehensive 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?

As we have mentioned above that it is a comprehensive tendon scanning system which works on non destructive testing principals to find out voids, water intrusion and bleeding grout in external tendons. This system also includes a device to detect section loss within the tendon.

Why was it developed?

During construction of complex bridges, tendons are filled in grout to prevent 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 developed this TendonScan system to resolve this problem.

How it is used?

It is a battery operated robotic system that uses the latest in non destructive testing and modern technology. This system couples itself with the tendon and travel along it to perform a MRI like inspection of the material inside it. The inspector stands on the mobile control unit which travels along 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 section of tendon is then illustrated in 3D color graphics so that any discontinuity like water intrusion, void or bleeding grout can be identified and quantified easily.

What problem does it solve?

This tendon assessment system helps in locating corrosion, voids, bleeding grout, section loss and other problems inside and outside the tendon. Moreover, it also helps in monitoring the discontinuities over a period of time which helps in deciding that when to repair or replace a post tension tendon. 

To know more about our products and services, you can visit our website https://www.infrastructurepc.com/ or contact us at info@infrastructurepc.com.