Concrete scaling refers to the local flaking or peeling of the concrete surface due to exposure to environmental conditions such as freezing and thawing. Factors that contribute to concrete scaling include low-strength concrete, the use of deicing salts, and a high water-cement ratio in the mix.
The initial phase of concrete scaling starts with small patches that can expand and merge into larger areas if not promptly repaired. Fixing concrete scaling involves cleaning the affected areas and resurfacing the damaged concrete.
How Does Concrete Scaling Occur?
Concrete scaling occurs when water within the concrete creates pressure due to repeated cycles of freezing and thawing. This pressure can cause the near-surface concrete to break away. Deicing chemicals intensify this effect by increasing the saturation of concrete and enhancing the frequency of freezing and thawing cycles.
In moderate cases, the depth of the scaled areas can range from 2.5 to 10 mm. In severe cases, concrete scaling can result in the exposure of aggregates and even their dislodgment.
Causes of Concrete Scaling
- Exposure to Freezing and Thawing Cycles Before Strength Gain: Concrete exposed to freeze-thaw cycles before it achieves the necessary strength (27 MPa) is susceptible to scaling.
- Use of Low-Strength Concrete or High Water-Cement Ratio: This type of mix allows deeper penetration of water and deicing chemicals, making the concrete more vulnerable to scaling.
- Insufficient Air Entrainment: Using non-air-entrained concrete or insufficiently entrained air results in a poor air void system within the hardened concrete.
- Improper Curing: Not following an adequate curing process increases the permeability of the concrete, reducing both its strength and durability.
- Short Curing Period: Insufficient curing time can lead to higher concrete permeability, reduced strength, and decreased durability.
- Lack of Concrete Protection After Placement: Failing to protect concrete after placement can make it susceptible to environmental damage.
- Improper Finishing: Incorrect finishing processes can trap water at the surface of the concrete, weakening its structure.
- Quick-Drying Concrete Surface: If the surface dries too quickly, it may not reach the designated strength, which increases the risk of scaling.
- Use of Deicing Chemicals on New Concrete: Applying deicing chemicals to fresh concrete increases the likelihood of scaling.
Effects of Scaling on Concrete
- Reduced Concrete Strength: Scaling diminishes the overall strength of the concrete.
- Compromised Durability: The long-term durability of the concrete is impacted.
- Concrete Spalling: Scaling can lead to more severe spalling if not addressed.
- Distorted Appearance: The visual appeal of the concrete is significantly affected.
- Increased Maintenance Costs: Repairing scaled concrete can be costly and time-consuming.
Preventive Measures
- Proper Concrete Mix Design: Ensure the mix has an appropriate water-cement ratio (maximum 0.45) and well-graded aggregates.
- Use a Suitable Curing Method: The curing process should be adequate and thorough.
- Sufficient Curing Period: Allow at least seven days of curing for the concrete to reach 27 MPa or 70% of its design strength, making it capable of resisting scaling.
- Avoid Premature Finishing Operations: Do not perform any finishing when there is water on the surface of the concrete.
- Prevent Premature Water Addition: Avoid adding water during troweling or floating before the bleeding process completes.
- Allow Bleed Water to Evaporate: Wait for bleed water to come to the surface and evaporate before starting the finishing process.
- Avoid Vibrating Screeds for High Slump Concrete: Using vibrating screeds on high-slump concrete can create a weak surface layer.
- Protect Against Corrosive Substances: Refrain from using deicing salts like calcium chloride, magnesium chloride, or sodium chloride on new concrete surfaces.
- Protect New Concrete: Shield new concrete from harsh environmental conditions and prevent full saturation before freeze-thaw cycles in winter.
- Ensure Proper Sloping: Slope the concrete surface appropriately to allow water drainage. Saturated concrete is more prone to freeze-thaw damage.
- Waterproofing: Clean the concrete surface and apply a waterproofing system every 3-5 years to prevent water and deicing solution penetration.
Repairing Concrete Scaling
- Remove Loose Concrete: Clear away any loose or flaking concrete and clean the surface thoroughly to remove dirt and debris.
- Dampen the Surface: Moisten the cleaned area and apply a thin layer of cement paste before placing the resurfacing concrete.
- Use Proper Resurfacing Concrete: Apply a suitable type of concrete for resurfacing, such as latex-modified concrete or polymer-modified cement concrete.
- Apply Pressure During Finishing: Ensure the application of pressure when performing finishing operations to achieve a durable surface.
- Seal Construction Joints: Seal joints with an epoxy resin sealer to prevent water infiltration and enhance durability.
Conclusion
Concrete scaling can significantly impact the strength, appearance, and durability of concrete structures. By understanding its causes and taking preventive measures, such as using a proper mix design and adequate curing, one can mitigate the risk of scaling. Timely repairs using appropriate resurfacing techniques ensure the longevity and performance of concrete, maintaining both its functionality and aesthetics.
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