2023-05-23 14:40:51

Spalling of concrete or concrete spalling is a phenomenon where a few parts of the concrete break themselves free from the structure and expose the reinforcement or the insides of the concrete to the atmosphere.

1. Inadequate Cover

Inadequate cover will increase the vulnerability of the reinforcement to the environment. Even the slightest crack on the surface will expose the reinforcement.

When steel comes in contact with water and air, it corrodes. The corrosion products have a higher volume than steel, causing high internal pressure and thereby causing spalling.

Solution: Proper structural design, proper supervision, or cautious handling of the materials.

2. Freeze-thaw Cycles

In cold-weather regions, the seeped water will turn to ice which is higher in volume than that of water.

Solution: This increased volume can be managed by creating artificial air pockets inside the concrete with the help of air-entraining agents.

3. Alkali Aggregate Reactions

When the alkali in the cement reacts with the silica in the aggregates in the presence of water, it will form the Alkali-Silica Gel (ASG), which is higher in volume than the conventional products of hydration.

Solution: Alkali aggregate reaction will not take place if any of the three elements – water, alkali or silica are not present. Therefore, the reaction can be incapacitated by reducing the alkali content in the cement or using silica-free synthetic aggregates.

4. High Temperature

Explosive spalling may occur during a fire or when concrete is exposed to high temperatures, which cause high pore pressure developed by oversaturation. High-strength concrete is more vulnerable to failure under high temperatures than that normal strength concrete due to the increased brittleness.

Solution: Increasing the fire safety of the building will reduce the risk of explosive spalling.

5. Improper Compaction

Improper compaction may leave the reinforcements exposed to the environment, initiating corrosion and thereby spalling.

Solution: Proper supervision and using vibrators to ensure proper compaction will rectify the problem.

6. Improper Water Content

Low water content will reduce the workability and make it hard for compaction. This may lead to the formation of unintended air pockets which may later pave a way for crack formation. High water-cement ratio will reduce the strength of the concrete thus making it more vulnerable to micro cracks and thereby spalling.

Solution: Correct mix design ratio, proper supervision has to be followed to avoid any mishaps during the mixing process.

7. Sulphate Attack

It is caused by sulphate rich cement or the sulphates present in the atmosphere. The decomposition of the products of the hydration reaction leads to reduction in the strength of the concrete and in doing so causes spalling.

Solution: Using sulphate resisting cement and decreasing the permeability of the concrete.

8. Chloride Attack

This occurs in the structures exposed to sea water. Chloride attack will directly cause corrosion to the steel reinforcements inducing the spalling concrete.

Solution: Increasing the concrete cover, coating the reinforcements with anti-rusting paints.

9. Rough Finishes

A rough surface finished structure tends to accumulate more water on the surface than a smooth surface finished structure. The rough finished structure will increase the seepage of water and may encourage spalling.

Solution: Provide smooth finishes.

10. Polluted Environment

The pollution in the environment will also cause chemical attack on the concrete. The pollutants with sulphide elements will combine with water and ingress into the structure and cause spalling.

Solution: This can be avoided by applying water repellent paints on the surfaces.