Concrete Scaling: Ways to Fix and Prevent it

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Concrete scaling is the local flaking or peeling off of the near-surface concrete due to environmental factors like freezing and thawing. Other factors that may contribute to the initiation of concrete scaling are the use of low-strength concrete, deicing salts, and a high water-cement ratio in a concrete mixture.

The process of concrete scaling begins with small patches, but develops and merges with the larger patches and broader areas if it is not repaired soon. The scaling in concrete can be fixed by cleaning the deteriorated areas and resurfacing the concrete.

How does Concrete Scaling Occur?

Essentially, water in concrete creates an expansive pressure due to repeated freezing and thawing cycles and leads to the breakaway of near-surface concrete. Deicing chemicals exacerbate the expansive water pressure as it increases the concrete saturation and freezing and thawing cycles.

In moderate cases, the depth of patches ranges from 2.5 to 10 mm. However, it leads to aggregate exposure and popping out of aggregates in severe cases.

Causes of Concrete Scaling

1. Exposure of concrete to freezing and thawing cycles before the concrete gains the required strength (27 MPa).
2. Use of low-strength concrete or high water-cement ratio, which facilitates deeper penetration of water and deicing solutions.
3. The use of non-air entrained or too little entrained air leads to poor air void system in hardened concrete.
4. Improper curing regime.
5. Curing concrete for a shorter period than required leads to the increase in  concrete permeability, reduction of concrete strength and durability.
6. Lack of adequate concrete protection after its placement.
7. Improper finishing may trap water in the concrete surface and subsequently reduce concrete strength.
8. Quick-drying of concrete surface prevents the concrete surface from achieving the designated strength. As a result, the risk of scaling increases.
9. The use of deicing chemicals for new concrete increases the likelihood of scaling.

Cases of Scaling of Concrete

The scaling of concrete may be divided into several cases, which are presented in Table-1:

Table-1: Cases of Concrete Scaling

Cases of scaling	Description	Surface loss
Light	Aggregates are not exposed	Concrete surface loses mortar
Medium	Exposure of coarse aggregate	Loss of concrete layer (thickness ranges from 0.5 to 1 cm)
Severe	Loss of mortar around aggregates	Loss of concrete layer (thickness ranges from 1 to 2 cm)
Very severe	Loss of surface mortar and coarse aggregate particles	Loss of concrete layer (depth is greater than 2 cm)

Effects of Scaling on Concrete

1. Reduced concrete strength
2. Compromised concrete durability
3. Concrete spalling, if not repaired soon
4. Distorted appearance of concrete
5. Increased maintenance cost

Preventive Measures

1. Design concrete mix properly; use appropriate water-cement ratio (maximum 0.45) and well-graded aggregate.
2. Use a suitable curing method.
3. The curing period should be long enough (minimum seven days) for concrete to gain a strength (27 MPa or 70% of design strength) that can resist scaling.
4. Do not carry out finishing operations when water is on the concrete surface.
5. Prevent the addition of water when concrete is troweled or floated prematurely.
6. Do not perform finishing works before bleeding water comes to the concrete surface. So, let bleed water come to the surface and evaporate, and then begin the finishing operation.
7. Prevent vibrating screed for high slump concrete as it creates a weak layer of concrete surface.
8. Avoid the exposure of concrete to corrosive substances. For example, salts like calcium, magnesium, or sodium chloride for new concrete surfaces.
9. Protect newly placed concrete from severe environmental conditions and avoid full saturation of new concrete before freezing and thawing cycles during the winter season.
10. Slope the concrete slab surface properly to drain water. Saturated concrete is at risk of freezing and thawing and subsequent surface deterioration.
11. Clean concrete slab surface and apply a suitable waterproofing system every 3-5 years to prevent penetration of water and deicing solutions.

Repairing Concrete Scaling

1. Remove loose concrete and clean the surface of any dirt and debris.
2. Dampen the cleaned concrete area and apply a thin layer of cement paste before concrete placement for resurfacing.
3. Place proper concrete type to resurface the damaged area. Latex-modified concrete (polymer-modified cement concrete) is a good option.
4. Apply pressure on the concrete while the finishing operation is being performed.
5. The construction joints can be sealed with an epoxy resin sealer.

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