What is Concrete Cancer?
“Concrete Cancer” a generic term often used to describe cracking and spalling concrete in buildings. Concrete cancer indicates a severe problem which requires remediation.
Concrete in buildings is often concrete with steel bars inside it to act as reinforcement in the tension zones of the concrete.
The “cancer” term is often used as this is a problem which once it starts, tends to grow and spread until eventually, it will affect the structural integrity of the building. This type of deterioration is a problem best attended to in the early stages when it has not spread. Addressing this issue as soon as possible is likely to minimize the extent of damage, which in turn reduces the remediation costs.
The problem occurs in steel-reinforced concrete elements, such as balconies, edges of floor slabs and concrete wall panels.
What causes concrete cancer?
Over time moisture and salts permeate into and move through the concrete. This moisture will eventually encounter the steel reinforcement bars, causing the steel to rust. As the steel bars rust, they expand causing the concrete around them to crack and spall.
This cracking, along with the associated rust staining on the concrete, are the typical telltale signs of concrete cancer.
As the concrete cracks, it then allows easier water penetration to the steel bars, accelerating the process.
There are several important factors which will determine how quickly concrete cancer is likely to occur. These are:
- the proximity of the building to the sea or an industrial area. Airborne salts will cause a problem much faster.
- is the concrete sealed or painted, thus reducing moisture and salt penetration?
- is it good quality concrete (ie strong and impervious) or is it poor quality concrete which allows more moisture and salt intrusion?
- how much concrete is there around the steel bars? The greater the concrete cover, the longer it will take for the salts to get to the steel and hence the longer to start rusting.
- how old is the building? The older the building, the more time the moisture and salts have had to penetrate the concrete.
How important is it to treat concrete cancer?
The steel reinforcement bars in the concrete act as tension tie rods and are vital for the performance of the concrete element.
If concrete cancer occurs, it will:
- reduce the cross-section of steel reinforcing bar able to act as a tension tie
- spall concrete off the outside of the element, breaking it apart.
Hence, the concrete element becomes more and more ineffective and unable to do its job.
It should be noted that concrete cancer deterioration in one part of a concrete element may render the entire member ineffective.
When should concrete cancer be treated?
It is important to treat the concrete cancer as early as possible. Leaving it untreated may lead to the spreading of the rusting along the steel bars, or extensive loss of cross-section of the steel bar, which affects its ability to perform.
If the rusting of the reinforcement is allowed to spread along the reinforcement bars it means that a much greater area needs to be treated, rather than a small area. This increases the cost of the remedial work.
If the rusting of the steel reinforcement is allowed to continue unabated, the cross-sectional area of the bar may reduce or the bar may break. This then means that the remedial work will need to include replacement of the steel reinforcing bar, at a much higher cost than treating the bar when only slightly rusted.
We have had several cases where steel-reinforced concrete balconies have had to be cut off the building and completely rebuilt, as the concrete cancer was so severe that they could not be saved. Don’t leave your concrete cancer untreated until it is too late!
What can be done to treat concrete cancer?
We can specify many ways to treat and remediate the concrete cancer.
In the early stages, treatment can be as simple as cleaning and painting with specialised products. However this may still be expensive, depending on the extent of damage and ease of access to the affected areas.
In later stages of concrete cancer, the repair work is much more involved and may include replacement of steel reinforcement and extensive patching.
Other remedial work may be specified, depending on site conditions, such as the installation of galvanic anodes to slow future corrosion.
The above advice is generic only and cannot be taken as site-specific for a particular case.
Each case needs to be assessed and reported on individually by an experienced structural engineer, who will specify particular remedial work for that building and site.
For more information on Concrete Cancer Treatment please contact Magryn.