We’ve been talking a lot lately about corrosion. There are many corrosive elements that impact building structures from water to oxygen to mold. Today we are going to be talking about one of the elements we are constantly battling: salt.
Chloride ions, found in de-icing salts and marine environments, present a major threat to the durability and strength of building structures. Over time, exposure to chloride ions leads to the corrosion of steel reinforcements, deterioration of concrete, and damage to other critical elements. Understanding how chloride ions impact these components is essential to implementing effective preventative strategies and maintaining structural integrity.
How Chloride Ions Affect Building Elements
1. Steel Reinforcement in Concrete
Chloride ions directly attack steel reinforcements in concrete. When they penetrate concrete, they break down the protective oxide layer surrounding the steel, causing it to rust. As rust forms, it expands, putting internal pressure on the surrounding concrete. This pressure causes cracking, spalling, and ultimately weakens the structure. Over time, foundations, columns, and load-bearing components can lose their strength if left untreated.
2. Concrete Structures
Concrete also suffers when chloride ions infiltrate. They penetrate through cracks or porous areas, reducing the alkalinity of the concrete and allowing corrosion of the embedded steel. This leads to surface cracks, spalling, and delamination, which worsen as chloride ions continue to seep in. Without proper maintenance, the concrete’s strength will degrade, eventually requiring extensive repairs or even replacement.
3. Roofs and Foundations
In coastal areas or regions where de-icing salts are used, chloride ions damage roofs and foundations. Roof membranes, particularly those with metal components, can deteriorate over time due to salt exposure, resulting in leaks and corrosion. Foundations that come into contact with groundwater containing chloride ions face similar risks, as the steel reinforcement corrodes and weakens critical support structures.
High-Risk Areas for Chloride Ion Damage
You’re most likely to see chloride ion damage in coastal regions, where salt-laden air permeates building materials. In cold climates where de-icing salts are regularly used, chloride ions can splash onto structures like bridges, parking garages, and buildings near treated roads. Buildings exposed to frequent salt contact or those with poor drainage or waterproofing are at higher risk of chloride-induced damage.
Prevention and Maintenance Strategies
Preventing chloride-induced damage is crucial for preserving a building’s structural integrity. Here are some practical steps to prevent or minimize chloride damage:
1. Apply Sealants and Protective Coatings
One of the most effective ways to prevent chloride ion penetration is by applying protective sealants to exposed concrete surfaces. Silane and siloxane-based coatings create a water-repellent barrier that blocks moisture and chloride ions from entering the concrete. For steel reinforcements, anti-corrosive coatings can be applied before embedding them in concrete. This forms a protective layer that shields the steel from chloride exposure and corrosion.
2. Use High-Quality Concrete Mixes
Choosing dense, low-permeability concrete mixes helps reduce the likelihood of chloride infiltration. By adding materials like fly ash, slag, or silica fume to the mix, you can lower the permeability of the concrete and slow the movement of chloride ions. Ensuring proper curing and maintaining the right water-cement ratio also creates stronger, more durable concrete, making it less vulnerable to chloride ions.
3. Incorporate Corrosion Inhibitors
Adding corrosion inhibitors to concrete mixes is another powerful way to combat chloride ions. These additives prevent or slow down the corrosion process by neutralizing the effect of chloride ions. Some inhibitors form a protective film on the steel surface, while others modify the electrochemical environment inside the concrete, reducing the likelihood of corrosion.
4. Install Cathodic Protection Systems
Cathodic protection provides an advanced method for preventing steel corrosion in chloride-rich environments. This system applies a small electrical charge to the steel reinforcement, converting the steel into the cathode of an electrochemical cell. This prevents the steel from corroding, even in highly corrosive environments. Though more costly, cathodic protection works well for structures exposed to high levels of chloride, such as bridges and marine structures.
5. Ensure Proper Drainage
Maintaining good drainage minimizes chloride exposure by preventing water and salts from accumulating around the structure. Proper slope grading, drainage channels, and waterproofing measures can significantly reduce the risk of chloride penetration into foundations and other critical structural elements.
6. Perform Regular Inspections and Maintenance
Regular inspections allow you to detect early signs of chloride-induced corrosion, such as rust stains, cracking, spalling, and discoloration. By addressing these issues promptly, you can repair damaged areas before they become major problems. In chloride-rich environments like coastal or road-adjacent areas, frequent inspections and proactive maintenance are key to preventing significant damage.
Consequences of Neglecting Prevention
Failing to take these preventive measures leads to serious structural issues over time. Chloride-induced corrosion, if left unchecked, weakens concrete, rusts steel reinforcements, and reduces the structure’s load-bearing capacity. You may face large-scale projects, such as concrete replacement, steel reinforcement repairs, or even full structural rehabilitation, if corrosion progresses unchecked. In severe cases, neglected corrosion can lead to partial or complete structural failure, posing significant safety risks and requiring costly emergency repairs.
Conclusion
Chloride ions pose a significant threat to building structures, especially in areas exposed to salts, such as coastal regions or roads treated with de-icing agents. However, by applying preventive measures like protective coatings, using high-quality concrete, adding corrosion inhibitors, and performing regular inspections, you can dramatically reduce the impact of chloride ions. Neglecting these precautions can lead to costly repairs, loss of structural integrity, and potential safety hazards. Early intervention and consistent maintenance are key to preserving the strength and longevity of buildings exposed to chloride ions.
