Tendon failure in prestressed structures is rare—but when it happens, the consequences can be serious.
Over the past 40 years, I’ve seen how small oversights can lead to large problems.
Whether due to material, workmanship, or detailing, tendon failures are almost always preventable—if we know what to look for.

This article outlines the most common causes of tendon failure in bridges and buildings across Asia—and more importantly, how to avoid them.

1. Incomplete or Poor Grouting

Cause:

Inadequate grouting leaves voids that allow moisture and contaminants (especially chlorides) to enter and corrode the prestressing steel.

Typical Signs:

• Corrosion near anchorages or at high/low points
• Red or brown stains at ducts
• Lack of back-pressure during grouting
• Empty vents when cropped after grout has set

How to Avoid It:

• Use a grout mix with tested properties: fluidity, bleed resistance, expansion (including inclined tube wick effect)
• Use mixers and pumps of adequate type and capacity to ensure continuous operation
• Verify duct filling at vents (and hammer-sound external tendons)
• Use borescopes to locate voids where suspected
• Never skip grout trials or training—even on routine jobs
• Consider alternative materials such as wax or grease in aggressive or inaccessible environments

2. Misalignment Between Ducts and Anchorages

Cause:

If the duct is misaligned relative to the trumpet or trumplate at the anchorage, stressing loads may not transfer properly.
This can cause local stress, gaps, or even puncturing of the sheath.

Typical Scenario:

• Diaphragms cast with misaligned formwork tubes
• Trumpet-to-duct connections adjusted manually on site
• Gaps and shear stress at duct connections

How to Avoid It (External Tendons):

• Carefully check duct alignment during diaphragm casting
• Use softened, thermally flexible trumpet connectors if misalignment is minor (with proper control)
• Inspect trumpet positioning with a borescope or camera prior to stressing

3. Poor Tendon Layout or Detailing

Cause:

Improper layout can lead to excessive curvature (tight radius), kinks, or clashes with reinforcement—all of which increase local stress and complicate grouting.
Improper vent positioning and sizing is also a frequent issue.

Common Mistakes:

• Ambitious tendon profiles in thin decks
• Conflicts with rebar or embedded items
• Neglect of splay forces at anchorages

How to Avoid It:

• Follow ETA or system-specific detailing rules (minimum curvature radius, etc.)
• Use 3D layout coordination—especially in congested structures
• Review tendon forces, splay zones, and curvature carefully during design
• Build and assess mock-ups when introducing non-standard layouts

4. Inadequate Protection in Harsh Environments

Cause:

In coastal or industrial environments, PT tendons are exposed to aggressive elements—salt spray, humidity, pollution—that accelerate deterioration.

Risk Zones:

• Tendon anchor blocks
• Segment joints in segmental construction
• Exposed external PT ducts on viaducts
• Poorly sealed grout vents and anchor caps

How to Avoid It:

• Use corrosion-resistant sheathing and ensure full sheath continuity
• Seal all vents, couplers, and anchor caps thoroughly
• Apply multi-layer protection: wax + HDPE duct + anchorage cap
• Schedule periodic inspections—even on relatively new structures

5. Poor Execution at the Anchorage Zone

Cause:

Anchorage protection is often rushed or overlooked, even though it is one of the most critical zones in a PT system.

How to Avoid It:

• Inspect anchorage reinforcement and geometry before casting
• Use certified personnel for stressing and grouting
• Conduct post-installation inspections, especially for sensitive structures

6. Neglected Inspection and Maintenance

Cause:

Many structures are left without any post-construction inspection or maintenance.
Early signs of tendon degradation often go unnoticed—until intervention becomes urgent and costly.

How to Avoid It:

• Implement a structured tendon inspection plan (especially for external PT)
• Use tools such as borescopes, tapping, or corrosion sensors to monitor condition
• Document all installation records for future reference
• Educate asset owners and operators on what to check, and when

Final Thoughts

Tendon failure is rarely about defective steel—it almost always results from poor detailing, careless execution, or lack of follow-up.
The good news is: all of these can be prevented with proper planning, training, and controls.

At MONBALLIU Consulting, we’ve helped project teams identify, avoid, and resolve tendon issues
in bridges, viaducts, and buildings throughout Asia. If you suspect tendon problems—or want to ensure your project avoids them—get in touch.