WHY YOU NEED TO KNOW ABOUT CONCRETE CANCER AND HOW BEST TO AVOID IT
Concrete cancer is the term given to the gradual destruction of concrete caused by rusting of embedded steelwork as a result of water penetration and can lead to a building's structural integrity being compromised. When water penetrates concrete through fine cracks or weathered, porous surfaces, it rusts the structural steel within which then expands. When the steel expands it creates more concrete cracks allowing for more water penetration, cancer spread and eventual spalling (when concrete starts to fall off a building), which will continue, if left untreated.
worn surfaces: unprotected, porous surfaces lead to water absorption and concrete cancer.
cracked / fractured concrete: cracks provide water access to the steel reinforcement
instigating concrete cancer and fracturing the concrete enabling further water penetration.
moisture stains and ponding: inadequate drainage causes water to settle into concrete
leading to concrete cancer.
failing control and expansion joints: joints that do not facilitate concrete movement can lead to concrete fracturing and concrete cancer.
inadequate concrete cover: steel reinforcement too close to the surface makes it easier for water absorption resulting in concrete cancer.
rust stains: when water comes into contact with steel reinforcement, the steel rusts.
rusted balustrade fixings: rust spreads to the embedded concrete starting the concrete cancer process.
bubbling paint: paint that appears to be bubbling i.e. on soffits, often means concrete cancer is present.
hollow surfaces: concrete surfaces that seem hollow usually have concrete cancer.
exposed steel reinforcement: concrete cancer causes concrete to break away exposing the steel reinforcement.
10 POSSIBLE SIGNS OF CONCRETE CANCER
Concrete cancer is the term given to the process where rusting structural steel begins to rust and in doing so expands, creating stresses and fractures in the surrounding concrete. This process is ongoing if not addressed according to structural engineer specifications. If left to develop, the fracturing concrete allows further areas of moisture penetration in-turn leading to the development of larger and more numerous areas of concrete cancer. This process is ongoing if the rusting steel is not correctly addressed and the surfaces are left with no waterproof coating. In time, initial small areas of concrete cancer become larger and more expensive to repair. In our experience this equates to growth in the damage of approximately 5% per year, directly impacting repair costs.
Once repairs are carried out, and robust, flexible, non-slip waterproof coatings applied, the repairs and original surfaces are protected from the development of new instances of concrete cancer. Setting aside a budget for these repairs is a priority to prevent cost increases, and to maintain the structural integrity and value of the asset. As a general rule :
Concrete cancer repairs cost around $900 - $1,200 + GST / sqm to repair (extent of repairs increase 5% annually).
Waterproof coatings (which act to prevent the onset of further concrete cancer) cost $90 - $135 + GST/ sqm to supply and install.
As the above rates demonstrate, the repair and prevention of concrete cancer is of the utmost importance for the owners in terms of maintaining the value of their asset and preventing high repair costs in the future.
Concrete cancer observed in various areas as nominated which is attributable to / evidenced by;
FRACTURED CONCRETE ELEMENTS
Fracturing in concrete leading edges, soffits, beams and columns is most commonly due to the onset and development of concrete cancer. These areas may present with visible surface rust stains, localised fracturing, and sound ‘drummy’ when tapped with a hammer. These require complete breakout to reveal clean steel, rust removed from all surfaces of the steel, and concrete reinstated to paintable finishes using specifically engineered structural patching materials. The methodology used by Conspar since 1996 is verified and recommended by Structural Engineers and is fully detailed in our 'Site Specific Specifications (SSS)'.
Furthermore, exposed areas of steel elements connected to / through concrete such as steel beams, lintels and balustrade fixings, are often the weakest point in regard to the onset and development of concrete cancer in buildings. These elements provide a link between exposed weathering surface areas and the structural substrate, and it is often the case that the steel elements begin to rust first, causing fine cracks and fractures at the interface of steel and concrete elements. In time this damage grows, eventually leading to the rust spreading deeper into the substrate and attacking the structural reinforcing in the concrete in below and adjacent to these areas.
In order to address the various types of structural damage, and importantly, correctly address the source of the issue in order to provide long-term solutions for the property owners, a selection of the following works may be required:
a. Repair and rectify all areas of concrete cancer as detailed in the 'Site Specific Scope of Work (SSW)' which is compiled following a site visit. The relevant repair methodology as specified in the nominated material Product Data Sheet is then applied.
b. Structural steel posts with signs of deterioration in the form of rust build-up at base plate and head plate locations, and surface corrosion generally; Where localised repair by mechanical abrasion of rust and correct sealing of the steel are not sufficient, damaged structural steel posts are replaced with new, hot-dipped galvinised posts. In some cases such as in marine environments these will also be factory-coated in protective coatings to provide higher performance protection. These coating systems are produced independently by industry material specifiers and detailed for the owners in the 'Site Specific Specifications (SSS)'