Don t let Concrete Cancer destroy your biggest asset!

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1 CONCRETE CANCER & CONCRETE SPALLING EXPLANATION BY JOHN F. JOHNSON, SR. PARTNER M.A.C. CORP PANAMA Don t let Concrete Cancer destroy your biggest asset! What is Concrete Cancer? Concrete Cancer is caused by many factors: Factors Include: carbonation, moisture, efflorescence and salt. When concrete cracks, water penetrates through causing the steel reinforcement deep inside to rust. Rusting steel then sheds its skin forcing the layers of rust to expand and push away the concrete surrounding it. This results in large (the size of a car in the case of the Franklin D. Roosevelt Freeway on the East River side of NYC) or small pieces (in the case of the Seacliff Apartment in SA) of concrete cracking and/or falling away and allowing steel reinforcement to become even more corroded and may cause devastating structural weakness (wear) on both the steel and the concrete. DETECTION On the outside of the affected concrete rust stains are visable, broken concrete or even rusted steel reinforcement poking through the concrete slab, walkway, eave, awning, facade, garage, flat roofs, balcony edges etc.

2 However, what is not detectable by the human eye is the spread of the "cancer" throughout the concrete, and will continue to spread if left untreated. Concrete Cancer and Spalling Repair Concrete cancer is caused when the steel reinforcing within a concrete slab begins to rust. As steel rusts it can expand up to 7 times its original size causing the surrounding concrete to be displaced and become flakey. As the steel pushes the concrete away, more water gets to the steel expediting the process. The process is often referred to as concrete spalling. Continually washing/hosing, as is being carried out on the Seacliff Apartments only serves to exacerbate the problem. Tell-tale signs of Spalling Concrete Unless one is a structural engineer, or have seen the signs before, chances are signs of spalling are not recognized and completely disregarded, even when it's time to organise concrete cancer repair work. Here are a few key signs indicating the need for structural repair. Flaking and cracking concrete (concrete spalling) Rust stains which seem to leak out from within the concrete Bubbling of concrete render or Leaks which appear in the roof or internal walls As often as not, observers mistake these signs as general weathering and dilapidation, caused by the elements; but whilst this is true to some extent and may play a part in exacerbating the problem, the real problem lies within the concrete itself. Risks of Spalled Concrete Whilst all will agree that spalled concrete is an eye-sore, what many people fail to realise is that as time goes on, concrete cancer also represents a potential OH&S hazard. Over time, and with increased exposure to the elements, untreated pieces of concrete may fall from the structure. If these fall from heights in high traffic areas, then passers-by will be at risk of injury, and other buildings in proximity, at risk of damage as well. Spalling and delaminated concrete should be repaired immediately, as deferring the decision to treat it will inevitably lead to increased problems into the future. 2

3 How Concrete Cancer Begins The process can start in many ways, but generally it is due to one of the following: Poorly treated reinforcing steel being used when the slab is poured The ends of the reinforcing being too close to the surface. As water seeps through the concrete it picks up limestone and other chemicals. When it hits the steel it causes oxidation to occur in the form of rust Incompatible metals being used in close proximity to each other, thus causing a reaction which allows water into the slab Stress fractures from bearing weight or general wear and tear allow water to penetrate the concrete and react with the steel Poorly installed window and door lintels are exposed to the elements causing rusting to occur Furthermore, any attempts to fix the problem for the short-term (such as rendering over the problem) will only exacerbate the issue. Despite, potentially looking better, the rusting process will continue below the surface causing the steel to again displace the concrete and in some cases rust so badly the steel eventually needs replacement. Treatment and repair of the concrete is the best solution. Concrete Cancer Repairs The M.A.C. Corp Panana team have a certain expertise in this field, however at the present time we do not operate within Australia. There are however reputable Groups who do provide a full service in Australia (albeit through Agents), one of which is FOSROC. FOSROC use a Product for this purpose known as Galvafroid / Galvashield, however we would recommend that if you do engage FOSROC, that you request them to use a MAC Product as MAC far out-performs Galvafroid (See FOSROC Test Summary). FOSROC staff are trained in the identification of the underlying issues causing your visible and structural defects. Ideally you should request your Repairer provide you with a scope of works, a repair methodology and an estimate before they begin the process of repairing your concrete. In brief summary they should remove all drummy concrete and brick work, grind back the reinforcing steel to remove all rust and treat the steel with anti-corrosive membranes (or replace the steel if required). Once the steel underneath has been treated they should then reinstate the actual concrete and the visual component (bricks or render) to restore the original facade. It may also require that the entire building be further protected with a cathodic device. Where the issue has originated in the base and floor by floor slabs or on the roof of the building structure, it is likely that waterproofing will also need to be undertaken. 3

4 Once the rusted reinforcing has been repaired, application of a waterproofing membrane will help prevent the ingress of moisture to the slab and prolong the life of the steel and therefore the structure itself. CAUTION: Sadly, as often as not, fixing concrete cancer is just one part of the problem. Depending on the nature of your building, its age or the cause of the original problem, you may need more than just spalling repair. 4

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