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Peering Into The Health Of Bridges

May 31st, 2018   Author: Doug Thaler

IPC's TendonScan® creates history by enabling X-Ray vision into post-tensioned tendons to arrest corrosion on bridges.

Technology is a great enabler of data gathering. That is an undeniable reality of contemporary life. Unfortunately, it is a reality that many still want to suppress or ignore.  American writer and Professor of Biochemistry, Isaac Asimov said, “I discovered, to my amazement that all through history there had been resistance … and bitter, exaggerated, last-stitch resistance … to every significant technological change that had taken place on earth.” 

 

Suhail Doshi, CEO of digital analytical company, Mixpanel, said, “Most of the world will make decisions by either guessing or using their gut. They will be either lucky or wrong.”

A nation’s infrastructure is too precious and too enmeshed with human lives, to leave decision-making to guessing or gut feeling. 

 

Data is a crucial factor in deciding what is wrong with a piece of infrastructure, especially the aging bridges of the United States.

 

Bridges are necessarily held together with post tensioning, a technique developed in the 1930s to reinforce concrete. In 1933, a young French civil servant, Eugene Freyssinet, produced three large pre-stressed concrete girders and inserted them underneath the quay in LeHavre, in France, to prevent its collapse.

post tension tendon inspection

Post Tension Tendon Inspection 

Over the years, civil engineers began using post-tensioned cables for safety of large concrete structures. Millions of miles of such cables, embedded in grout and enclosed and sealed in rubberized exteriors, known as post-tensioned tendons, support and hold up hundreds of thousands of bridges and highways in the US. They enable larger spans, thinner slabs and greater distances between support columns of bridges.

In building complex bridges, these post-tensioned tendons are filled with grout to prevent corrosion. Low quality grout and admixtures and improper grouting procedures could, subsequently, lead to separation of grout within the tendon. The grouting creates a high alkaline environment to prevent corrosion, but grout separation leads to low pH grout at tendon points and anchorage, creating vulnerability to corrosion in these locations.

 

It is a fact that corrosion is a significant reason for degradation of bridges. It is also a fact that corrosion of post-tensioned tendons in complex bridges have become a significant problem in recent times. In 2016, a report by the Department of Transportation refers to “severe corrosion” of post-tensioned tendons in certain bridges.  The report explains that the corrosion with reference to separation of grout and the high moisture content in the immediate environment. However, one of the cited bridges was built in 2003. The question arises why the corrosion went unnoticed in this specific bridge for 13 years, and was only being looked at when the condition had considerably worsened. 

 

Back in 1998, the US Federal Highway Administration, (FHWA), estimated the annual cost of corrosion on highway bridges as $8.3 billion.  The worldwide corrosion authority, NACE International, headquartered in Houston, Texas, estimates the current annual direct cost of corrosion on highway bridges as $13.6 billion.

 

More than a fourth of the 607,380 bridges in the US are over 50 years old, and 108,000 of the bridges are constructed with pre-stressed concrete. All bridges are supposed to be inspected every 2 years, but that does not happen consistently. Even when inspections are done, it is still the archaic visual inspection or listening to the change of tone by hitting the cable with a hammer. These outdated methods lead to subjective, often inaccurate conclusions. Critical clues are missed through human error.

 

In contrast, there is a technology called TendonScan® developed by the Florida-based robotic engineering firm, Infrastructure Preservation Corporation (IPC), which is a portable robotic instrument to inspect post-tensioned cables with an MRI-like radiological image of the cable interior. Following six years of R&D, IPC has added TendonScan® to its service range, able to scan the inside of the tendon and locate vulnerability to corrosion by analyzing air, water and bleeding grout within the tendon. 

 

Using the latest Non-Destructive Evaluation (NDE) and Non-Destructive Testing (NDT) technologies, the TendonScan® is able to track the size and shape of the developing abnormality, and guide timely and necessary repairs with razor-sharp accuracy. Locating developing issues before they become problems, and paving the way for early repair, extends the lifecycle of tendons and saves millions of taxpayer dollars.

 

TendonScan® is comprised of two separate patented portable units. The first is a 16 lb battery-operated unit that travels along a tendon, and employs Electrical Capacitance (EC) imaging to view the inside of the tendon.

 

The second unit utilizes magnetic flux leakage to locate loss of metallic area within a post-tensioned tendon.

TendonScan® is comprised of two separate patented portable units. The first is a 16 lb battery-operated unit that travels along a tendon, and employs Electrical Capacitance (EC) imaging to view the inside of the tendon.

 

The second unit utilizes magnetic flux leakage to locate loss of metallic area within a post-tensioned tendon.

 

TendonScan® is comprised of two separate patented portable units. The first is a 16 lb battery-operated unit that travels along a tendon, and employs Electrical Capacitance (EC) imaging to view the inside of the post tensioned tendon. The second unit utilizes magnetic flux leakage to locate loss of metallic area within a post-tensioned tendon.

The inspector observes the scanning process at the control station located on a mobile cart, and walks along with the sensor. The sensor uses wireless connectivity to transmit MRI-like images to the control station. 

 

The inspection scans through the grout of the tendon’s insides, identifying locations and quantities of water, air, and bleeding grout. 

 

The inspector, then, makes real-time assessments, with a proprietary tendon condition assessment report that identifies locations and sizes of irregularities, which is delivered to the bridge owner. 

For more information on post tension tendon inspection services:

 

TendonScan® provides valuable quantitative data the Department of Transportation needs to prioritize and maximize allocation of scarce resources for repairs. 2013 Nobel laureate in economics and Professor of Economics at Yale University, Robert J. Shiller, said, “Some of the best theorizing comes after collecting data because then you become aware of another reality.”

 

TendonScan® is able provide baseline condition assessment, monitor healthy tendons for preventative maintenance or locate corrosion, and, has surpassed all available technology to inspect post-tensioned tendons in bridges. 

 

Corrosion in construction, especially steel and concrete bridges, is notoriously stealthy. Furthermore, bridges have to endure so much – vagaries of the weather like icy winters and blistering summers, heavy traffic and emissions and steel-unfriendly ice-melting salts. All of these conditions contribute to rusting of bridges.

 

If ignored, corrosion can lead to deadly consequences like total collapse of bridges.

Engineering firms realize they can make a much larger profits from utilizing modern technology and robotics as part of their inspection protocol than the current manual method. In addition they can provide their clients with more quantitative data that allows the asset owners to both help extend the service life of their critical infrastructure assets as well as help prevent potential catastrophe.  

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