Underground Infrastructure Under Attack:

How Metrorrey Line 1 Stopped Corrosion Before It Became Catastrophic

Every day, millions of people rely on transit infrastructure they never see.

Hidden behind walls and beneath city streets are tunnels, stations, and structural systems that must perform reliably for decades. Yet many of these assets face the same invisible enemy:

Corrosion.

When corrosion takes hold inside reinforced concrete, deterioration accelerates:

• Concrete begins to crack and delaminate

• Reinforcing steel loses section and strength

• Water intrusion increases

• Maintenance costs escalate

• Service life rapidly declines

This was the challenge facing Line 1 of the Metrorrey transit system in Monterrey, Mexico.

The Challenge

Engineers discovered significant deterioration throughout portions of the tunnel system, including:

Visible Signs of Distress

• Exposed, corroded reinforcing steel

• Delaminated concrete surfaces

• Loss of concrete alkalinity

• Carbonation-related deterioration

• Water infiltration through walls and ceilings

• Cracking caused by trapped moisture

Previous coating installations had inadvertently trapped water within the structure, accelerating degradation and creating conditions that promoted further corrosion.

Without intervention, the deterioration cycle would continue to worsen.

The Objective

The project team needed a solution capable of:

• Halting active corrosion

• Protecting embedded reinforcing steel

• Improving concrete durability

• Reducing permeability

• Strengthening deteriorated concrete

• Extending service life

• Minimizing future maintenance requirements

Most importantly, they needed a solution that would work within the concrete itself—not simply cover the problem.

The SURTREAT Solution

SURTREAT implemented a comprehensive rehabilitation program utilizing:

TPS XII

Vapor Phase Corrosion Inhibitor

Provides corrosion protection by migrating through the concrete matrix and forming a protective molecular barrier around reinforcing steel.

TPS II

Ion-Exchange Densification Technology

Strengthens and densifies concrete while reducing porosity and moisture movement throughout the substrate.

Phase 1: Surface Preparation

Successful rehabilitation starts with proper preparation.

Key Activities

• Dustless abrasive blasting using Garnet 30/60 media

• Removal of deteriorated coatings

• Exposure of affected concrete surfaces

• Cleaning of contaminated areas

• Verification inspections before treatment

Why It Matters

Proper surface preparation allows treatment technologies to penetrate the concrete matrix and perform as intended.

Phase 2: Corrosion Mitigation with TPS XII

TPS XII was applied to areas exhibiting active corrosion.

Benefits

• Migrates through concrete as a vapor phase inhibitor

• Protects reinforcing steel

• Stabilizes corrosion activity

• Reduces future chloride-induced deterioration

• Extends reinforcement service life

Application Method

• Spray-applied for complete coverage

• Designed to penetrate areas surrounding embedded steel

Phase 3: Concrete Densification with TPS II

Following corrosion treatment, TPS II was applied to improve the condition of the concrete itself.

TPS II Delivered

• Reduced concrete porosity

• Enhanced tensile characteristics

• Improved moisture resistance

• Increased durability

• Improved resistance to future deterioration

Application Process

• Multiple treatment applications

• Controlled water misting between coats

• Absorption verification inspections

Unlike conventional coatings, TPS II works within the concrete matrix, modifying the substrate rather than simply creating a surface film.

Results That Matter

Corrosion Inhibition

• Active corrosion was stabilized

• Reinforcing steel received long-term protection

• Future chloride-induced damage was significantly reduced

Improved Concrete Performance

• Reduced porosity

• Enhanced structural properties

• Improved resistance to cracking

Restored Structural Integrity

• Deteriorated areas were stabilized

• Tunnel infrastructure returned to a safer operating condition

• Asset longevity was improved

Long-Term Water Resistance

• Reduced water accumulation

• Improved durability

• Lower anticipated maintenance requirements

The Bigger Lesson

The Metrorrey project demonstrates an important reality facing infrastructure owners worldwide:

The most effective rehabilitation strategies address deterioration at its source.

Instead of repeatedly applying coatings that can fail over time, infrastructure owners are increasingly looking for technologies that:

• Stop corrosion internally

• Strengthen existing concrete

• Reduce permeability

• Extend service life

• Lower life-cycle costs

By combining corrosion inhibition and concrete densification, SURTREAT helped transform a deteriorating tunnel into a protected and strengthened asset prepared for decades of continued service.

Is Your Infrastructure Showing Similar Signs?

Watch for:

• Water infiltration

• Rust staining

• Delaminated concrete

• Spalling

• Exposed reinforcing steel

• Carbonation damage

• Recurring maintenance issues

These are often early warning signs of deeper deterioration occurring within the concrete matrix.

Learn How SURTREAT Can Help

If your tunnels, parking structures, bridges, wastewater facilities, marine assets, or transit infrastructure are showing signs of deterioration, SURTREAT can help evaluate the condition and develop a solution focused on extending service life—not just covering symptoms.

Protect the asset. Preserve the investment. Extend the service life.