Concrete cancer is a problem many buildings can face. This phenomenon occurs when the internal framework, made from steel bars or mesh, is exposed to water or air. This exposure creates a build-up of carbonic acid which in turn creates rust, corroding the steel reinforcement. If no action is taken by the owners or tenants, this rust and decay will spread across the floor and into the walls, causing severe structural issues for the building. There have been numerous occasions where entire buildings have had to be pulled down and rebuilt as a result of concrete cancer. In other cases, such as the Champlain Tower in Miami, untreated concrete cancer caused the building to collapse which led to the death of three people. In this blog, we discuss the causes of concrete cancer, first signs of concrete cancer and the remedies.
Concrete Spalling Vs Concrete Cancer
Before dissecting concrete cancer, its causes and its potential remedies, it is important that we distinguish between concrete spalling and concrete cancer. These words are often used interchangeably. Concrete spalling describes the physical degradation and break-down of the concrete or cement rendering. Concrete cancer on the other hand refers to the spread and, if left untreated, worsening of concrete spalling. Although in most situations, concrete spalling is usually a sign of concrete cancer, these terms are not completely synonymous. Concrete spalling may also occur as a result of:
This is when water seeps into concrete structures through capillary absorption. This water is then frozen, creating micro cracks in the concrete surface. When the ice melts and temperatures rise, this damage is revealed. This cycle then repeats, increasing the number of and enlarging the microcracks. These cycles are typically seen where buildings endure below 0 degree temperatures such as Russia or Canada.
Poor Finishing Techniques
Many people believe that poor concrete finishing techniques only impact a floor or walls aesthetic value. Although this correct to a certain degree, the incorrect use of proper construction techniques can lead to Concrete Discoloration, Concrete Scaling, Concrete Curling, Concrete Crazing, or Concrete Cracking. To assist in minimising and reducing the discoloration of concrete it is imperative to ensure that the contractor has prepared the proper subgrade and subgrade uniform. It is also important to make sure that the worker does not finish the concrete prior to it bleeding. Concrete scaling is what happens when the concrete contains inadequate strength. Scaling sees the concrete slab flake off and or peel away. This may occur during freeze and thaw cycles. Concrete scaling can also occur when concretes are non-air-entrained or too little entrained air. Concrete Curling sees the bending of a concrete slab. This bending occurs as a result of different moisture and temperature levels between the top and bottom surfaces. A method of preventing this is making sure that the subgrade is damp during warm weather. It is also important to be careful when initially pouring the concrete mixture as segregation may occur, meaning, more moisture is found at the top of the concrete slap and less at the bottom. Workers should use proper control joints and should be vigilant when placing the steel reinforcements. Concrete Crazing is the inter connection and network of fine cracks and fissures. Although this does not impact the concrete’s strength or have any adverse effects on the concrete’s durability, it does look extremely unappealing when wet. This is caused by attempting to finish the concrete too early. Furthermore, it is important to make sure that no water is added to the concrete during the finishing process. Finally, concrete cracking can be caused by the improper compaction of the subgrade. It is important to make sure that all topsoil, organics and soft spots are removed from the surface as this will allow for proper compaction and help reduce the chances of settling.
The process of curing concrete can be defined and describing as providing adequate time to allow the concrete to achieve the desired properties for its intended use. It also is inclusive of providing adequate moisture and temperature for the concrete when pouring. Good concrete curing should see the enabling of prolonged hydration and the formation of a well-developed microstructure. When concrete is cured incorrectly or inadequately, reduced compressive strength development and increased drying shrinkage may occur. As such its abrasive resistance, durability and strength are all impacted, leading to concrete spalling.
A bad concrete mix
A bad concrete mix is usually a result of using incorrect quantities of cement or water, not creating a concrete mix that has been batched correctly for its application and may also be the result of recycled materials.
Causes of Concrete Cancer
Although concrete cancer can happen to any building in any location, there are several certain environmental factors that may prove to be predispositions for a building with concrete cancer. As concrete cancer can be caused by water, areas that are near the ocean may be locations of concern. Furthermore, locations and destinations around the world that contain extreme climates and weather conditions such as Mawsynram in India, which has been crowned the wettest inhabited place in the world, are also perfect conditions for concrete cancer to occur. Structurally speaking, properties with flat roofs are far more prone to concrete cancer as water is able to sit on this roof with very little to no run off. Other common triggers of concrete cancer may include design flaws and the incorrect implementation of materials throughout the construction phase such as the inadequate preparation of the reinforcing steel, incompatible support metals, poorly poured or insufficient concrete cover and finally, stress fractures from excessive weight and the close-to-surface positioning of the steel reinforcement. Poor waterproofing is a large catalyst for concrete cancer. The triggering of concrete cancer may occur when there a gaps or spaces around the membrane.
Signs of Concrete Cancer
Although there are many ways concrete cancer can rear its ugly head some common signs include crumbling, flaking or cracking of concrete as well as the appearance of rust stains or bubbling on the concrete or cement render. As the steel reinforcements and concrete weaken, more and more leaks will appear within the roof and walls.
How to Remedy Concrete Cancer
As stated, concrete cancer can be a very expensive, if not, fatal issue if left untreated or misdiagnosed. It is important to understand and know the variety of remedies that may occur as to best suit your budget. As such, the first step in remedying your concrete cancer is giving a civil or structural engineer a call. These engineers will come to your property and diagnose the issue at hand as well provide suggestions as to which methods you may choose to tackle this issue. Some methods of removing concrete cancer may include the site specific electro-chemical treatment (usually chose for properties near the ocean) or the simple removal of damaged concrete and the impacted steel. Of course this steel and concrete will be replaced with new material. Your chosen civil and structural engineer may apply an anti-carbonation coating in order to preserve the concrete.
It is important to keep an eye on your floors and walls as concrete cancer and subsequently, concrete spalling can spring up on residents of any property quite quickly. Individuals don’t notice concrete cancer in its early stages (it’s almost impossible to) so it is important to be extra vigilant when looking at your concrete when it appears on surface level, visible to the human eye. If you have noticed any strange marks on your concrete such as rust spots or bubbling and/or flaking or crumbing of your concrete send us an email at firstname.lastname@example.org or give us a call on 02 9518 0775 to speak to one of our expert engineers today.