What does concrete spalling mean?

Spalling is the deterioration of steel reinforced concrete and is characterised by the appearance of cracks and red rust. In severe cases, sections of concrete become completely detached from the steel reinforcing bar (known as "rebar"), exposing the bar to the elements.

What does concrete spalling mean?

Spalling is the deterioration of steel reinforced concrete and is characterised by the appearance of cracks and red rust. In severe cases, sections of concrete become completely detached from the steel reinforcing bar (known as "rebar"), exposing the bar to the elements. Spalling is a term used to describe areas of concrete that have cracked and detached from the substrate. There are a number of reasons why spalling occurs, including freeze-thaw cycles, the expansive effects of the alkali-silica reaction or exposure to fire.

However, the most common cause of spalling is corrosion of embedded steel reinforcing bars or steel sections. Corroded steel can expand up to ten times its original volume, putting stress on the surrounding concrete. Concrete spalling is a common problem in which part of the surface becomes detached, broken or spalled. Also known as spalling, it is the result of a weak surface that is susceptible to damage.

Concrete spalling describes the state in which concrete begins to degrade or flake off. The most common signs are cracking, crumbling or flaking of the concrete, rust stains or bubbling in the concrete or cement plaster, as well as leaks in the ceiling and walls. Spalling is the flaking or detachment of small particles of cement paste from the near-surface of the finished slab. In most cases, the defect does not affect the service life of the slab if left untreated.

The symptoms of concrete spalling are flaking, chipping and large chunks showing on the surface of the concrete, exposing the coarse, rocky concrete aggregate. These are the symptoms, but concrete spalling is more complex than just the appearance of the surface. Concrete spalling is the result of a chemical and physical process that occurs within the concrete itself. It is a relatively common problem with a number of causes ranging from how the concrete was mixed to environmental conditions.

Both conditions create a weak layer of concrete that is prone to breaking upwards when exposed to freezing. The type of repair and the work involved depends on where the concrete spall is located, how deep it is, whether it is on a vertical or horizontal surface, and whether there is any exposed rebar. Remedies may include specific electrochemical treatment for properties close to the ocean or simply removal of the damaged concrete, cleaning or removal of the affected steel and replacement with new material. Overworking the surface can damage or destroy the air bubbles found in air-entrained concrete.

ACI 318 (Building Code Requirements for Structural Concrete), which is the industry standard in the USA for the design and construction of structural concrete elements in buildings and structures, prescribes the minimum concrete "cover" for all reinforcing steel within that concrete element. Corrosion of reinforcing steel in concrete is a problem that has the potential to cause a wide range of problems ranging from economic to aesthetic. Concrete resurfacing is used to repair and revitalise concrete surfaces that suffer from things as minor as staining and light corrosion due to the elements, to more structural problems such as spalling. Concrete spalling is a defect that appears in a hardened concrete structure or slabs located in colder climates, where the concrete slowly breaks down into small flakes known as spalling from a larger solidified concrete body.

Corrosion is known to affect all concrete buildings and structures around the world, at least to some extent, and huge amounts are spent on addressing these problems. Concrete is porous, so it absorbs the acid created during the spalling process, accelerating corrosion and exposing the internal steel structure to air and water. Over time, due to the force applied by the freeze-thaw cycles along with the internal pressure of the expanded water, the top layer of concrete tends to peel off leaving pit marks, concrete fragments or spalling. The reason why some concrete structures show widespread spalling while others appear to be in good condition is due to a combination of age, maintenance, concrete quality, depth of the concrete layer and local environmental conditions.

The concrete cover varies according to the different exposures of the concrete element and the conditions under which it was formed. The concrete cover is the thickness of concrete between the outer edge of the concrete member and the rebar, which covers or protects the steel from exposure to the outside elements. In some cases where the concrete is new, a waterproofing sealer should be applied one month after the concrete is placed, as well as every few years thereafter. Spalling is typically observed in a concrete slab or concrete overlay in locations that have colder climates and experience the constant destructive forces of cyclic freezing and thawing (freeze-thaw cycle).

Riley Ryan
Riley Ryan

Subtly charming twitter aficionado. Evil web trailblazer. Total beer trailblazer. Professional bacon maven. Prone to fits of apathy. Alcohol fanatic.