What is concrete cancer?
Concrete cancer refers to the progressive deterioration of reinforced concrete, usually triggered by the corrosion of the embedded steel reinforcement (rebar). As the steel rusts, it expands up to 7 times its original volume, placing internal pressure on the surrounding concrete. This causes the concrete to crack, break away, and delaminate—exposing more steel to moisture and oxygen, accelerating the cycle.
This degenerative process compromises the structural integrity of buildings, balconies, beams, and facades. It’s especially common in coastal, humid, or poorly maintained environments.
How to Identify Concrete Cancer
Concrete cancer is often misidentified as general cracking or wear. However, early detection can save thousands in remediation. Here are key signs to look for:
Rust stains on concrete surfaces (often appearing as vertical streaks)
Cracking in a horizontal or stepped pattern, often near corners or edges
Spalling – flaky or crumbling concrete, especially when pieces break off
Delamination – a hollow sound when tapping the surface with a hammer
Exposed or corroding rebar
Leaking through cracks in balconies, suspended slabs or basements
If you observe a combination of these symptoms, there’s a high chance of underlying reinforcement corrosion.
Credit to Building Rectification Services
What Causes Concrete Cancer?
There are several factors that contribute to the development of concrete cancer:
1. Moisture Ingress
Water is the primary enemy. It enters through cracks, porous surfaces, or unsealed joints. Once inside, it reaches the rebar and initiates corrosion.
2. Carbonation
Over time, carbon dioxide from the atmosphere reacts with the calcium hydroxide in concrete, reducing its pH and compromising the protective layer around the steel. This process is known as carbonation, and it leaves the rebar vulnerable to rusting.
3. Chloride Attack
In coastal environments or structures exposed to harsh chemicals (pool chlorine), chlorides penetrate the concrete and aggressively corrode the steel reinforcement.
4. Poor Workmanship or Design
Inadequate concrete cover over the rebar
Use of low-quality materials
Poor compaction or curing
Cold joints and honeycombing
5. Movement or Cracking in the Structure
Ground movement, thermal expansion, or mechanical stress can lead to cracking, creating easy pathways for water and contaminants.
Significant structural cracking in a concrete wall has already led to ingress of its retained materials. The longer this crack is left open, the further the steel can degrade
Credit to Chicago Building Inspection
What Increases the Risk of Concrete Cancer?
Some factors significantly increase the likelihood of concrete cancer:
Proximity to the coast (high salt exposure)
Constant water immersion with the addition of chemicals (pools)
High humidity environments
Buildings over 20 years old without maintenance
Flat roofs and balconies that hold water
Structures with inadequate drainage or waterproofing systems
Even newer buildings are at risk if corners are cut during construction or if water ingress is not adequately addressed.
Why Concrete Cancer Must Be Addressed Early
Ignoring early signs of concrete cancer can lead to:
Expensive structural repairs
Potential safety hazards (especially in public or multi-residential buildings)
Loss of property value
Building code non-compliance
Ongoing moisture ingress and indoor mould problems
The longer the rebar is left exposed to moisture and oxygen, the more extensive the damage becomes. Delaying repairs may result in the need to replace entire structural elements rather than perform localised patch repairs.
How to Fix Concrete Cancer
There is no one-size-fits-all solution. The correct repair method depends on the extent of the damage, the cause, and the structure’s use. However, most repairs follow these essential steps:
1. Assessment & Diagnosis
Use of cover meters, corrosion detectors and rebound hammers
Infrared thermography or ultrasonic pulse tests
Visual inspection and sounding with a hammer
Professional inspection is crucial to map out affected areas accurately.
2. Remove Damaged Concrete
All loose, delaminated, or spalled concrete must be cut or broken away. This exposes the corroded steel underneath.
Credit to S & S Remedial
3. Treat or Replace Rebar
Clean rust from exposed reinforcement using mechanical tools or rust removers
Replace bars if corrosion has significantly reduced cross-section
Apply a corrosion-inhibiting primer to protect the steel from further attack
4. Install Galvanic Sacrificial Anodes
Galvanic sacrificial anodes are small metal discs or rods (usually made of zinc) that are connected to the steel reinforcement before patch repairs are carried out. They work by corroding in place of the steel – essentially "sacrificing" themselves to protect the rebar..
In simple terms:
The anode is a weaker metal that corrodes first.
It's electrically connected to the rebar.
Moisture and salts cause the anode to corrode instead of the steel.
This slows or halts the corrosion process, preventing concrete cancer from progressing
They're often embedded around the perimeter of repair patches or in areas prone to corrosion. Galvanic anodes provide long-term protection, especially in aggressive environments, and are commonly used in large infrastructure and marine repairs, but can be equally effective in residential settings.
5. Reinstate the Concrete
Use a polymer-modified repair mortar designed for structural repairs
Ensure proper bonding to the existing substrate with a bonding agent
Compact and finish in layers to avoid shrinkage cracking
Credit to Sika GBR
6. Waterproof and Seal the Area
Apply a breathable waterproof membrane or anti-carbonation coating to prevent further ingress of moisture and CO2.
Long-Term Prevention
To stop concrete cancer from returning:
Seal all cracks and control joints
Ensure good site drainage to divert water away from the structure
Apply anti-carbonation or silane/siloxane sealers
Perform regular inspections of exposed concrete
Use high-quality materials in future construction
In more serious cases, cathodic protection systems can be installed to reduce electrochemical corrosion activity in large concrete structures.
Professional Remediation
Fixing concrete cancer requires more than just patching a crack. If you’re dealing with a concrete structure that shows signs of deterioration, we recommend seeking expert guidance.
At TruBond Concrete Repairs, we offer:
Detailed inspections and reporting
Structural repair planning
Certified application of specialist systems
Waterproofing and surface sealing
Long-term maintenance solutions
We help strata managers, homeowners, engineers and builders get peace of mind—and extend the lifespan of their structures.
Concerned about concrete cancer?
Don’t wait. Contact TruBond Concrete Repairs for a professional assessment and practical repair plan tailored to your structure.