What Does a Concrete Shelling Look Like?

Descaling is a deterioration process that affects steel-reinforced concrete structures. Learn what peeling & chipping look like & how to prevent it.

What Does a Concrete Shelling Look Like?

Descaling is the deterioration of steel-reinforced concrete and is characterized by the appearance of cracks and red rust. In severe cases, the concrete sections are completely detached from the reinforcing steel bar (known as “rebar”), exposing the rebar to the elements. The symptoms of peeling concrete are flaking, chipping, and large pieces that you see missing from the concrete surface, exposing the aggregate of coarse, rocky concrete. Those are the symptoms, but the peeling of concrete is a bit more complex than the appearance at the surface level. The descaling of concrete is the result of chemical and physical processes that occur within the concrete itself.

It is a relatively common problem with a number of causes ranging from the way concrete was mixed to environmental conditions. Peeling concrete is a common issue where part of the surface flakes off, breaks or splinters. Also known as flaking, it is caused by a weak surface that is susceptible to damage. When steel is cast into concrete, naturally high alkalinity helps protect embedded steel from corrosion. However, this protection can be compromised by acidic atmospheric gases (known as carbonation), or by salts in concrete, typically from marine environments or de-icing salts.

When combined with oxygen and water, these contaminants create the perfect environment for corrosion. The reason why some concrete structures exhibit widespread flaking while others appear to be in good condition is due to a combination of age, maintenance, concrete quality, cover depth and local environmental conditions. It's not uncommon for contractors and concrete builders to receive calls from customers asking why their concrete is peeling and chipping, and how the problem can be solved. Descaled concrete may resemble round or oval depressions along surfaces. Descaling tends to be more common in cold climates when defrosting chemicals are applied or when seasonal freeze-thaw cycles damage concrete.

Beyond the obvious aesthetic problems, a reduction in cross-sectional area due to flaking and delamination weakens the concrete section. Delamination and chipping of a concrete member are undesirable conditions; they not only represent a potential impact hazard in the scenario in which chipped concrete falls and hits a person, but also reduce the cross-sectional area of the concrete member and decrease its ability to transport safely imposed burdens. The descaling of the concrete normally begins when the steel reinforcement embedded within the concrete member is oxidized. And if you have chipping, have it treated as soon as possible to maintain the structural integrity of the concrete as much as possible. The remedies for chipping vary depending on the severity of the problem, type and location of the structure and other factors. Over time, freeze-thaw cycles can weaken and crack the top layer of concrete, resulting in ugly notches and exposed aggregates. One technique that can prevent flaking is to apply a good water sealant to the finished surface to prevent water from entering the concrete. Rust on rebar takes up more space than original rebar, resulting in pressure build-up and consequently chipping.

CPT carries out concrete testing work as well as manufacturing state-of-the-art corrosion control technology. Splinters can appear because rebar has been exposed and moisture and water have started to rust it or because joints were not built properly. The cover is the thickness of concrete between outer edge of member and steel bar which covers or protects steel from exposure to external elements. Concrete is a good bet for durability, and its look has become increasingly sophisticated and artistic over time. Splinters can also be avoided if handled with care and appropriate techniques are used when pouring such as providing adequate coverage (embedding) of rebar and placing joints in right places at right distances. Concrete repairs must be carried out in accordance with BS EN 1504, European and British standard for repair and protection of reinforced concrete.