What is Concrete Cancer?
As the name implies – concrete cancer is a serious and wide spread problem where the expansion of oxides in reinforcing steel or rebar causes structural steel to expand up to eight times it’s original size, forcing concrete to delaminate. This unwelcome problem results in spalling where the concrete initially cracks, further accelerating the process, then breaks away. Once the concrete is compromised – initially through a small crack – this spalling process can quickly become severe with the threat of falling masonry a very real danger. Left unattended the structure itself can be compromised.
How do I know If I have It
- The early signs of concrete cancer include a localised brown discolouration on the surface of your concrete. This brown stain is the iron oxide leeching out of the concrete and is usually located close to a crack or small spalling.
- Any drummy sound when the concrete is tapped also indicates that you have a problem with concrete de-lamination with the most likely cause being concrete cancer.
How do I Repair Concrete Cancer
If you notice any of the above symptoms early intervention is definitely the best policy.
- Remove any spalling, cracked, or drummy concrete.
- Remove any concrete surrounding the rusty steel so you have access to it.
- Thoroughly remove as much rust as possible using a mechanical wire brush, scraper etc.
- Apply a quality rust converter thoroughly saturating the area. This will apply phosphoric acid to any rust remaining which is then converted to an iron phosphate coating.
- After 10 minutes wash off thoroughly and allow to dry.
- Depending on the application – repair the hole with an epoxy cementitious repair compound. First apply a slurry of the product which acts as a binder – let this semi dry. This is a specialised extra hard product purpose designed for concrete repair including structural applications and is available from Sica Australia PTY Ltd
What Causes Concrete Cancer
Concrete cancer is caused by one or more of the following;
- Rebar (steel) being located too close to the surface or sides of the concrete.
- Uneven concrete where standing water over time can compromise surface areas.
- Reduction in concrete alkalinity caused by certain aggregates and sands. Even though Portland cement is extremely alkaline a minimum PH8 is essential to avoid steel oxidation.
- Failure to repair minor cracks and damage to concrete in exposed areas.
General Concrete Repairs
Cracked concrete should be repaired ASAP as water inflow will increase damage rapidly.
Tip; Small long cracks can be sealed off from further water damage by cleaning out the crack making sure you leave no loose material. Brush away any dust or debris. Using a caulking gun, squeeze a bead of compound along the crack in sections that you can reach without moving. Using a finger or fine small sponge dipped in a mixture of washing up liquid and water and smooth out your bead of sealant. A clear silicon is ideal as there are no colour matching issues but specialised cloured caulking products can also be used.
Video – Repairing concrete