Concrete shedding is a state in which concrete starts to degrade or flake off. Common signs of this include cracking, crumbling, rust stains, bubbles on concrete or cement plaster, and leaks in the ceiling and walls. Concrete cancer, on the other hand, is the spread and worsening of concrete peeling. The concrete used in buildings is reinforced with steel and iron bars or meshes.
When exposed to air and water (for example, through leaks from a higher level), a weak carbonic acid begins to form and the bars start to corrode. Concrete is a porous material and can easily absorb surrounding elements, including this corrosive acid. Once corrosion sets in, the steel expands and causes the surrounding concrete to crack, which is known as chipping. This can trigger a vicious cycle by further exposing steel to the elements and accelerating the level of corrosion.
The impact on the building leads to a tragic compromise of structural integrity. Flat concrete roofs are an example of a building structure that is particularly vulnerable to leakage and water-driven concrete cancer if they are not adequately waterproofed. Waterproofing is one of the remedies to prevent concrete splintering and Projex Group supplies high-end PVC sheet membranes to achieve this. Once repairs are carried out and robust, flexible and non-slip waterproof coatings are applied, the original repairs and surfaces are protected from the development of new cases of concrete cancer.
However, corrosion of reinforcing steel is by far the most common cause of chipping and splitting in older concrete structures. In addition to living near the ocean with “common area windows open, leaving corridors with carpet and magnesite underneath to be exposed to the elements that led to the entire unit block having concrete chipping. Chipping is often caused by steel being placed too close to the edge of a concrete slab or because concrete is left uncoated and exposed to excessive weather. Rusty steel increases up to five times its original size, which displaces concrete and causes it to flake.
Over time, and with increased exposure to the elements, untreated pieces of concrete may fall out of the structure. The use of an appropriately qualified contractor is critical for repairing concrete chips, as is the diligent preparation of the substrate and selection of a repair material that is compatible with the host concrete. Freezing and thawing cycles, expansive effects of alkali-silica reaction, inadequate depth of cover over reinforcement, low-quality concrete cover on reinforcing steel, joint chips caused by poorly constructed joints leading to flaking of joints can also be important factors in causing concrete cancer. Concrete chipping will begin to damage both the concrete and steel reinforcement beams in the concrete slab. If left untreated, compromised concrete can quickly lead to serious structural problems that require extensive remediation.
When it comes to concrete repairs, it's important to seek a professional opinion from a reputable company such as Freyssinet. Corroded steel can expand up to ten times its original volume, putting stress on the surrounding concrete, which is why it's so important to start repairing concrete chips as soon as you notice them developing.