Protecting concrete from water is crucial for its longevity and structural integrity, preventing issues like spalling, cracking, and freeze-thaw damage. This is primarily achieved by making the concrete less permeable or water-repellent.
Concrete is inherently porous, allowing water and dissolved salts to penetrate, which can lead to various forms of deterioration. Effective protection involves using barrier coatings or penetrating treatments that prevent water ingress.
Two primary methods for protecting concrete from water, as indicated by the references, include using crystalline waterproofing and applying silane and siloxane-based water repellents.
1. Crystalline Waterproofing
Crystalline waterproofing is a method that uses special chemicals applied to the concrete surface or added to the concrete mix during batching. These chemicals react with water and cementitious particles within the concrete to form insoluble crystals.
- How it Works: The crystalline growth fills the pores, capillaries, and micro-cracks within the concrete mass. This makes the concrete impermeable to water from any direction, even under hydrostatic pressure.
- Benefits:
- Becomes an integral part of the concrete.
- Can seal minor cracks that develop later (self-sealing properties).
- Effective against both positive and negative water pressure.
- Long-lasting protection.
- Applications: Often used in basements, tunnels, water tanks, foundations, and concrete slabs exposed to moisture.
2. Silane and Siloxane Water Repellents
Silane and siloxane water repellents are penetrating sealers that do not form a film on the surface but rather soak into the concrete pores. They chemically react with the concrete substrate to create a hydrophobic (water-repelling) zone near the surface.
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How it Works: These silicon-based molecules penetrate the concrete and bond to the concrete's internal structure, lining the pores. This lining repels liquid water, preventing it from entering, while still allowing water vapor to escape (making the concrete "breathable"). This breathability is important as it prevents moisture buildup within the concrete itself.
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Types Based on Molecular Size:
- Silane-based water repellents: These are typically used for dense concrete surfaces like bridge decks, parking garages, and pavements. Silane molecules are smaller and can penetrate deeper into tight pore structures.
- Siloxane-based water repellents: These are generally used for more porous surfaces such as concrete facades, split-faced block, and pavers. Siloxane molecules are larger and are effective at repelling water from surfaces with larger pores or capillaries.
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Shared Characteristics:
- Excellent water repellency.
- Minimal or no change to the appearance of the concrete.
- Protect against freeze-thaw cycles and de-icing salt damage.
- Reduce efflorescence and staining.
- Note: These are surface treatments and do not offer protection against hydrostatic pressure from below the slab or behind walls.
Here's a comparison of the two main approaches based on the references:
| Feature | Crystalline Waterproofing | Silane/Siloxane Water Repellents |
|---|---|---|
| Mechanism | Forms crystals within pores & capillaries | Creates hydrophobic lining within pores |
| Penetration | Deep, becomes integral part of concrete | Penetrates near surface |
| Water Pressure | Effective against positive & negative pressure | Effective against liquid water penetration |
| Appearance | Typically no change (if integral/slurry) | Minimal to no change |
| Breathability | Can reduce some breathability (filling pores) | Highly breathable |
| Self-Sealing | Can seal minor cracks | No self-sealing properties |
| Application | Below-grade, water retention structures | Above-grade, traffic surfaces, facades |
Choosing the right method depends on the specific application, exposure conditions, and desired outcome. Crystalline waterproofing provides deep, structural impermeability, while silane/siloxane treatments offer surface-level water repellency and protection against surface-related deterioration.
