2025
The Silent Threat: How IE/PV Testing Can Detect Hidden Deterioration in Bonded PT Tendons
When it comes to infrastructure durability, bonded post-tensioning (PT) systems present a unique challenge. These systems are critical to the performance of major concrete structures such as bridges, yet their hidden nature makes them especially vulnerable to undetected deterioration.
The Problem: Corrosion Without Visible Warning Signs
Post-tensioned (PT) structures are designed for strength and durability, yet corrosion can develop undetected, leading to costly repairs or even structural failure. Traditional bridge inspections rely heavily on visual assessments, which fail to detect internal deterioration within PT tendons. By the time corrosion becomes visible, the damage is often severe.
In this blog, we will explore:
- Non-destructive testing (NDT) techniques that can be used to identify grouting defects where tendons are at risk of corrosion before it’s too late
- Proactive preservation strategies to extend the service life of PT structures
- Real-world case studies where corrosion remained undetected until failure
Why Early Detection Matters
- Bonded systems are vulnerable to hidden corrosion, often missed during routine inspections.
- Identifying deterioration early is critical to preventing costly failures and extending service life.
To gain deeper insights, join our upcoming webinar, where VCS Engineering experts will discuss these critical issues and real-world solutions.
How to Detect PT Corrosion Before It’s Too Late
Non-Destructive Testing (NDT) Methods
Engineers can use advanced NDT techniques to assess PT tendons without damaging the structure:
- Impact Echo (IE): Helps identify voids and discontinuities by measuring reflected stress waves.
- Pulse Velocity (PV): Measures the speed of ultrasonic waves through the concrete, helping determine material integrity and detect soft grout areas.
- Ground Penetrating Radar (GPR): Maps reinforcing details and evaluates structural integrity.
- Half-Cell Corrosion Potential Testing: Engineers can detect the risk of active corrosion in embedded steel by using the electrochemical potential difference between different points on a reinforced concrete structure.
These non-destructive techniques enable engineers to map grouting conditions without damaging the structure, making them perfect for evaluating the health of bonded PT systems. In the absence of these tools, engineers depend entirely on visual assessments, heightening the risk of overlooked failures.
Proactive Strategies for PT Preservation
To extend the life of PT structures, asset owners should go beyond standard inspections and integrate proactive maintenance strategies:
- Tendon Drying: Removes moisture trapped inside ducts to slow corrosion.
- PT Impregnation: Protects steel tendons from further deterioration.
- Regrouting of PT Ducts: Fills voids, stabilizing the structure and preventing moisture ingress.
These strategies, when combined with regular NDT testing, can prevent costly repairs and extend the service life of PT structures.
Case Studies: Investigating PT Corrosion Failures
Bridge in Virginia (Bonded PT Failure)
This Virginia bridge is a 4,868-ft cable-stayed bridge that spans the James River near Richmond, VA. It utilizes bonded PT tendons in its deck, superstructure, and substructure.
The Issue:
- A failed external tendon was discovered during a routine inspection—lying on the girder floor.
- Grouting defects (voids and soft grout) led to hidden corrosion undetected by standard inspection methods.
- Triggered a full investigation of internal and external PT tendons using advanced NDT methods.
Key Findings:
- Impact echo/pulse velocity testing identified 445 superstructure ducts and 43 pier ducts with grout voids up to 82 ft long.
- Voids in the grout allowed for moisture ingress, creating ideal conditions for corrosion.
- Standard visual inspections failed to identify the problem early.
- Advanced NDT testing could have prevented costly emergency repairs.
Bridge in Florida (Bonded PT Failure)
This Florida bridge is a 3,000-ft structure featuring external bonded PT tendons running longitudinally through box girders.
The Issue:
- The first sign of deterioration was a sudden tendon failure, with no visible warning signs.
- The owner requested a demonstration of PT testing techniques to assess the extent of potential grouting defects.
- Testing revealed severe voiding, soft grout, and active corrosion.
Key Findings:
- Lack of early detection resulted in unexpected and costly failures.
- Voids and soft grout allowed moisture ingress, accelerating corrosion.
Summary
In both cases, tendon failures served as the first—and only—visible sign of distress. Subsequent investigations revealed extensive voiding and soft grout conditions, which had allowed corrosion to silently progress inside the ducts.
Conclusion: Preventing Failures Through Early Detection
Corrosion in post-tensioning systems is a hidden but serious risk that can compromise structural safety. Advanced NDT methods provide early detection, helping engineers and asset owners take action before failures occur.
By integrating modern testing techniques and proactive maintenance strategies, infrastructure professionals can improve safety, extend service life, and reduce long-term costs.
To learn more about how to identify, assess, and prevent PT corrosion, join our upcoming webinar led by VCS Engineering experts.
Want to explore this topic further - Watch the Webinar now!
Natallia Shanahan and Pratik Murkute from VCS Engineering share additional insights, expand on the ideas shared in this blog, and walk through real-world examples in the Hidden Threats: Advanced Techniques for Investigating Corrosion in Post-Tensioned Structures webinar!
