Concrete spalling is a common problem in which part of the surface becomes detached, broken or spalled. It is usually caused by corrosion of reinforcing steel bars embedded in the concrete matrix, but can also be triggered by other factors such as inadequate preparation of reinforcing steel, incompatible supporting metals, metal bars placed too close to the surface, stress fractures due to excessive weight, insufficient concrete cover or poorly poured concrete. The environment in which the concrete element is placed has a significant effect on its performance in relation to durability. The most common source of spalling in brick, for example, is excess moisture in which water enters the brick material causing chunks of brick to flake off.
Spalling can be defined as the flaking or breaking of concrete particles from the surface of the concrete and exposure of the reinforcement to the atmosphere. The decomposition of the products of the hydration reaction leads to a reduction in the strength of the concrete and, in doing so, causes spalling. When the hydraulic pressure of the expanding ice exceeds the tensile strength of the concrete, the concrete scales loosen, exposing the aggregates. To repair spalled concrete, it is important to clean the affected area, including the reinforcement, use rust preventive paint on the corroded steel and then patch the spalled area with a concrete mix.
Concrete repairs should be carried out in accordance with European and British Standard BS EN 1504 for the repair and protection of reinforced concrete. Delamination and spalling of a concrete element are undesirable conditions; not only do they represent a potential road hazard in the event of the spalled concrete falling and striking a person, but they also reduce the cross-sectional area of the concrete element and reduce its ability to safely support the imposed loads.