Rebar rust is a severe hazard in concrete structures. .
So, it is essential for builders to know the signs of corrosion and how to stop it from forming
How Rusting Rebar Compromises Structural Integrity
Reinforcement corrosion is one of the most common causes of structural damage in concrete. Rebar can rust over years or months, depending on how exposed it is. Certain materials — particularly chlorides and salt — significantly accelerate the corrosion process.
Some builders may mistakenly overlook the possibility of corrosion since rebar is completely embedded in concrete. However, even a small crack in the surrounding concrete is enough to let water seep in and begin the corrosion process.
Rust can go unnoticed for an extended period unless large stretches of rebar are exposed. By the time the it is a structural stability hazard, it often requires expensive, intensive repairs. Corrosion is particularly dangerous on stretches of elevated concrete that rely on rebar to maintain tensile stability. As the rebar corrodes, the concrete slowly loses support. Eventually, any downward force can easily cause the concrete to collapse.
Corroded rebar can also give way rapidly with the slightest physical trigger. Sadly, this is exactly what happened in the 2021 collapse of a condominium building in Miami, Florida in the United States. The accident killed 98 people and occurred in a matter of seconds, leaving no time to evacuate. Afterward, investigators found large amounts of heavily corroded steel rebar, hinting at the building’s dangerously poor structural integrity.
How to Identify and Repair Rusted Rebar
How can builders find and remove rust from embedded rebar? The easiest approach is visual inspection. Severe corrosion usually occurs when concrete damage exposes rebar to the elements, so major hazards should be clearly visible. Keep an eye out for everything from thin cracks to chunks of missing concrete.
Consulting with a structural engineer is always a good idea before attempting any repairs. An expert can ensure repair personnel resolve the corrosion without further endangering the building’s structural integrity.
Builders usually fix rusty rebar using spot repairs. They start by removing the concrete surrounding the corroded section. Once the rebar is exposed, builders either remove the rust or remove the rebar itself, depending on the severity of the corrosion. If the rust is minor, they usually clean it off and leave the rebar in.
Builders can use a variety of techniques to remove layers of rust. For example, media blasting is one fast and effective solution. A low-density blasting media may be ideal for cleaning rebar since a small amount is highly effective, making it a good choice for covering a narrow surface area. In addition to media blasting, builders may also use wire brushing to remove rust.
The full extent of the corrosion is often visible only after repair personnel clean the rebar. So, the next step is a thorough inspection. At this stage, builders determine if the rebar is worth saving or if they need to replace it.
If they leave the rebar in, they cover it in a corrosion-resistant coating or sealant to prevent further damage. Otherwise, repair personnel remove the damaged rebar and install new, well-coated rebar. Afterward, they cover it with a fresh layer of crack-resistant concrete.
Tips and Tricks for Preventing Rust
It is worth noting all rebar has a low passive corrosion rate. So, over time, some amount of corrosion is inevitable. However, builders can take precautions to minimize the risk.
For instance, films and coatings can dramatically reduce rebar corrosion rates. The Australian Steel Institute maintains two standards covering rebar surface treatments — AS/NZS 5131:2016 and AS/NZS 2312 — which builders can use as a starting point. These standards outline the recommended surface treatment process and coating options. The two most common approaches are paint coatings and hot dip galvanizing.
Additionally, crack-resistant concrete mixtures minimize the likelihood of water getting into the embedded rebar. In wet or humid environments, it is a good idea to use a low water ratio in the concrete mixture to prevent internal chemical reactions and erosion. Builders can also finish concrete with water-resistant coatings as an additional defense against the elements.
Prevent Rusting Rebar to Ensure Structural Stability
Rebar corrosion is a common cause of structural damage, but there are ways to identify, repair and prevent it. Builders can start by conducting a physical inspection for cracks or concrete damage. Carefully clean, coat or replace any rusted rebar. Apply surface treatments on rebar and surrounding concrete to prevent future rust formation.