What Is Spalling Of Concrete ?
Spalling of concrete is a phenomenon where few parts of the concrete break itself free from the structure and expose the reinforcement or the insides of the concrete to the atmosphere.
Spalling is caused by certain chemical reactions inside the concrete which lead to the formation of foreign products which are of high volume. These new products due to lack of space inside the concrete will increase the internal pressure. As a result, cracks are formed to release this pressure outside.
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| Civil Insta |
Causes Of Spalling Of Concrete
- Corrosion of Embedded Metals
- Inadequate Cover
- Freeze thaw Cycles
- High Temperature
- Alkali Aggregate Reactions
- Improper Compaction
- Improper Water Content
- Sulphate Attack
- Chloride Attack
- Rough Finishes
1. Corrosion Of Embedded Metals
As described earlier, steel uses for the reinforcement, so the corrosion of the steel and other embedded material cause the deterioration of concrete. When steel rust the resultant corrosion occupies a large volume than the steel.
2. 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 products of the corrosion have high volume than that of steel causing high internal pressure and thereby causing spalling.
3. Freeze thaw Cycles
In cold weather regions, the seeped water will turn to ice which is higher in volume than that of water.
4. High Temperature
Explosive spalling may occur during fire or when concrete is exposed to high temperature which causes high pore pressure developed by the oversaturation. High strength concrete is more vulnerable to failure under high temperature than that of normal strength concrete due to the increased brittleness.
5. Alkali Aggregation Reactions
When the alkali in the cement reacts with silica in the aggregate in the presence of water, it will from the alkali silica gel which is higher in volume than the conventional products of hydration.
6. Improper Compaction
Improper compaction may leave the environment initiating corrosion and thereby spalling.
7. 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.
8. Sulphate Attack
It is caused by rich cement or the sulphate 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.
9. Chloride Attack
This occur in structures exposed to sea water. Chloride attack will directly cause corrosion to the steel reinforcement inducing the spalling concrete.
10. Rough Finishes
A rough finished surface 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.
Repair Of Spalling Of Concrete
- Remove the concrete at the spalled areas to expose the corroded steel bars.
- Clean the exposed area of steel bars with wire brush to remove the rust from the bars.
- Clean the exposed area with compressed air.
- Apply two coats of anti-rust paint to the steel bars.
- Before patching the area, apply a bonding agent to the affected surface to ensure proper adhesion.
- The affected area shall be filled with normal concrete or polymer modified cement mortar.
