How to Evaluate and Mitigate Corrosion in Reinforced Concrete Structures

Reinforced concrete is the backbone of our built infrastructure. Yet, hidden within these critical structures lies a persistent threat to long-term durability: corrosion of the steel reinforcement. Over time, corrosion can lead to cracking, delamination, and spalling, which impact structural durability and safety.

What Causes Corrosion in Reinforced Concrete?

At the core of the problem is a chemical reaction. When moisture, oxygen, and contaminants such as chloride ions penetrate the concrete cover together, they disrupt the highly alkaline passive oxide film, which acts as a protective layer surrounding embedded steel reinforcement. Over time, the corrosion reaction causes a buildup of rust, which is greater in volume than the original steel.  This rust applies pressure on the surrounding concrete, causing cracks, surface delamination and eventually concrete spalling.

The two main reasons behind corrosion in reinforced concrete are:

• Chloride Ingress: Often from de-icing salts or marine exposure; chlorides break down the passive layer protecting steel reinforcement.
• Carbonation: A natural process where carbon dioxide reduces the pH of concrete, allowing corrosion to initiate. Often found in structures in urban environments with high carbon dioxide levels and pollutants. Think parking structures, tunnels and even historic/old buildings.
  
  

Understanding these mechanisms is essential for engineers, asset owners, and maintenance professionals aiming to design resilient structures and preserve aging ones.

More details here on why corrosion happens.

Corrosion Mitigation for Existing Concrete Structures

While new construction can incorporate materials and designs to mitigate corrosion, existing infrastructure requires thoughtful intervention, including:

• Improved Cement Mix Design: Using low-permeability concrete and supplementary cementitious materials to reduce the ingress of harmful contaminates.
• Surface Treatments and Coatings: Sealers, membranes, and coatings act as physical barriers, which can help mitigate chloride and other contaminant ingress.
• Cathodic Protection: Galvanic and impressed current systems that protect the steel from further corrosion and concrete degradation.

These methods extend the service life of infrastructure and can be tailored to each structure's environmental exposure and condition.

How Do We Assess Corrosion Damage? NDT and Destructive Techniques Explained

Evaluating structural health is a critical first step before choosing a repair or rehabilitation approach. If you don’t know what’s wrong, how will you know the best way to fix it?

Non-Destructive Testing (NDT):

Non-destructive testing (NDT) techniques allow us to assess the condition of concrete structures without damaging them. These tools are fast, efficient, and essential for identifying hidden deterioration, mapping corrosion activity, and guiding targeted investigations.

• Impact Echo/Pulse Velocity: Determines concrete characteristics and identifies delamination, cracking, and voids.
• Ground-Penetrating Radar (GPR): Identifies steel reinforcement locations and concrete cover depth and provide a qualitative assessment of the condition of reinforced concrete.
• Corrosion Potential Mapping: Measures the electrochemical potential difference between two points to determine corrosion risk.

Corrosion potential test being performed on concrete bridge substructure.

Concrete Material Testing:

These testing methods give us critical insight into the internal condition of concrete and reinforcement. These techniques help validate corrosion risks and structural performance, especially when planning long-term repairs.

• Carbonation Depth: Determines how far CO₂ has penetrated the concrete, lowering pH and increasing corrosion risk. We also evaluate concrete cover to assess the remaining service life.
• Chloride Concentration: Concrete powder samples are tested to measure chloride levels at various depths. This helps assess corrosion activity and informs service life modeling.
• Compressive Strength: Core samples are tested to confirm concrete strength and structural capacity—key for load ratings and safety assessments.
• Petrography: Microscopic analysis identifies deterioration mechanisms like freeze-thaw, ASR, and sulfate attack, while also detailing the original mix composition.

Carbonation depth test performed on concrete core.

By combining both types of assessment, engineers and owners can gain a comprehensive understanding of the damage—and can confidently determine whether to repair, protect, or replace.

Why It Matters: The Economic and Safety Impacts of Corrosion

Corrosion-related deterioration contributes to billions of dollars in global infrastructure repair annually and accounts for over 3% of global GDP. Early identification and targeted mitigation strategies can help avoid costly shutdowns, extend service life, and protect public safety.

Want to explore this topic further?

Pratik Murkate from VCS Engineering  shares additional insights, context, and answers your questions during our upcoming webinar on May 21st, 2025 - Corrosion 101: Causes and Assessment Strategies . 

Register Now