Protecting Post-Tensioned Parking Structures: Understanding and Managing Corrosion Risk

Post-tensioned (PT) concrete has transformed how we design parking structures. Its efficiency allows for longer spans, thinner slabs, and open layouts that make modern facilities possible. In the first part of The Parking Structure Durability Series, we explored how modern inspection techniques move engineers from visual observation to data-driven evaluation, creating a clearer understanding of corrosion risk and structural health. The same concept holds true for post-tensioned systems. Finding corrosion early can prevent a manageable maintenance task from turning into a significant repair.

PT systems are known for their strength and cost efficiency, but that performance can only be maintained if the internal steel tendons remain well protected. When those tendons are exposed to moisture or chlorides, corrosion can begin out of sight and progress long before visible warning signs appear. The result is a system that may appear sound on the surface while deterioration advances inside.

This is why engineers and asset owners must look beyond design efficiency to focus on durability management. The long-term reliability of post-tensioned parking structures depends not only on how they are built, but on how well they are monitored, maintained, and protected over time.

Why This Matters

 The corrosion of PT tendons is often invisible until failure occurs. A single ruptured tendon can:

• Disrupt load distribution within a slab or beam
• Cause cracking or deformation of surrounding concrete
• Lead to progressive loss of capacity or serviceability
• Trigger costly, large-scale intervention

Unlike conventional reinforced concrete, deterioration in a PT system often progresses invisibly until it becomes a serious issue. Surface cracking or rust staining may only appear after internal corrosion has developed. For owners and engineers, this means that by the time the problem becomes visible, repairs can already be complex and costly.

Identifying the root causes of deterioration early helps maintain safety and prevents the need for large-scale structural repairs.

The Challenge of Seeing What You Cannot See

Inspecting post-tensioned structures is as much about interpretation as it is about data collection. Engineers rely on experience and judgment to read subtle clues that reveal what is happening inside the concrete.

Visual inspection, radar scanning, and targeted sampling all provide valuable information, but their greatest value comes from how they are analyzed together. It takes experience to tell the difference between a harmless surface crack and one that signals tendon distress, or to interpret data from ground-penetrating radar in light of construction practices and exposure history.

This is where expertise becomes critical. A structure might look fine on the surface, but an experienced engineer knows that even small breaks in tendon protection can let in water and chlorides, leading to hidden corrosion.

How Do You Identify Problems in Post-Tensioned Structures?

  

Assessing corrosion risk in post-tensioned systems requires more than just looking for surface damage. The most effective programs combine visual inspection with selective testing and interpretation guided by recognized standards such as ACI 222R, ACI 562, and ASTM C876.

A well-designed condition assessment typically includes:

• Visual evaluation to locate distress patterns such as cracking, rust staining, or moisture accumulation near anchorages.
• Non-destructive testing such as ground-penetrating radar (GPR) or ultrasonic methods to confirm tendon alignment and detect voids or potential breaks.
• Selective exposure and sampling of tendon anchorages or ducts to verify corrosion or confirm sheath continuity.

These tests provide critical data, but interpretation determines their value. Each structure’s history, age, exposure conditions, and design details influence corrosion behavior.

For example, a parking structure exposed to de-icing salts may have the same chloride levels as one in a coastal environment, yet the deterioration mechanisms differ. One might show end anchorage corrosion due to poor drainage, while the other experiences sheath degradation from salt-laden air and thermal cycling.

The value lies in how those findings are synthesized to define both the cause and extent of deterioration. This level of interpretation transforms test results into actionable insight, allowing engineers to design repair and protection strategies that address the underlying mechanism rather than only treating visible damage.

From Repair to Preservation

Once deterioration is confirmed, the goal shifts from short-term repair to long-term preservation.

Common approaches include tendon replacement, anchorage rehabilitation, and crack or joint sealing. However, these must be paired with a strategy that addresses the underlying corrosion mechanism. That may mean re-establishing proper waterproofing, improving drainage, or introducing cathodic protection to control active corrosion.

Each repair should be evaluated under the guidance of ACI 546R (Guide to Concrete Repair) and ACI 562 (Assessment, Repair, and Rehabilitation of Existing Concrete Structures). The objective is not only to restore capacity, but to prevent recurrence.

What Are the Best Corrosion Mitigation Strategies?

Protecting PT systems over the long term requires a proactive plan rooted in standards and proven technologies. Guidance from ACI 222R, ACI 222.3R, and ASTM G1 outlines best practices for corrosion protection design and monitoring.

Common strategies include:

• Cathodic Protection (CP): Galvanic or impressed current systems can prevent corrosion by maintaining steel in a passive condition. Proper design and monitoring per ACI 222R and ACI 222.3R are critical to ensure safe current distribution.
• Surface-applied corrosion inhibitors: Penetrating treatments that reduce corrosion activity at the steel interface.
• Protective sealers and coatings: Regular maintenance of deck membranes limits chloride ingress.
• Drainage and joint maintenance: Proper water management prevents accumulation near beam pockets and anchorages.
• Ongoing corrosion monitoring: Periodic half-cell potential testing in accordance with ASTM C876 verifies that protection systems remain effective.

The most successful programs integrate several of these measures. The goal is to create a durable, low-risk environment for the embedded steel rather than rely on any single layer of defense.

Why Early Maintenance Is Critical for Post-Tensioned Structure Durability

The most effective corrosion mitigation begins early, ideally within the first few years of service. Routine inspections, proactive sealing, and surface protection can prevent moisture intrusion before it reaches the tendons. Neglecting early maintenance often leads to accelerated deterioration that demands complex and costly tendon replacement later.

A planned maintenance program:

• Reduces exposure to chlorides and water
• Detects small issues before they grow
• Lowers lifecycle costs
• Extends service life

Early intervention is not just preventive; it is a measurable way to protect both safety and investment.

Moving From Risk to Reliability

Post-tensioned systems offer strength and efficiency, but that strength depends on ongoing protection. The ability to interpret data, understand corrosion mechanisms, and apply targeted solutions separates reactive repair programs from long-term durability management.

For engineers and owners, this means moving from reactive repair toward proactive reliability, supported by consistent testing, monitoring, and continuous improvement.

Protecting Post-Tensioned Parking Structures: Evaluation, Repair & Corrosion Mitigation Strategies

Join our experts as we explore practical approaches to evaluating post-tensioned systems, diagnosing corrosion, and implementing proven protection techniques.

Date: December 3, 2025
Time: 6:00AM – 7:00AM CST  | 1:00PM – 2:00PM CST
Register: https://www.wesavestructures.info/events/category/Parking-Structure-Durability

This is the second session in The Parking Structure Durability Series, focused on proven strategies for maintaining the strength and longevity of your parking assets.