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Tunnel environments are uniquely harsh, characterized by constant moisture, piston-effect air pressure from passing vehicles, and the necessity for high fire resistance.

Key Technical Requirements

1. Fire Performance & Passive Protection

In a tunnel, a fire can reach extreme temperatures very quickly (the RWS curve or HCinc curve). Tunnel boards must be Class A1 Non-combustible.

• Thermal Insulation: The board must protect the structural concrete or steel lining from “spalling” (where moisture in concrete expands and causes the surface to explode).
• Toxic Fumes: They must be zero-smoke and zero-halogen to ensure visibility and breathability for evacuees.

2. Durability & Hydrophobic Properties

Unlike standard siding, tunnel boards are often exposed to groundwater seepage and high-pressure washing.

• Water Absorption: High-quality tunnel boards are autoclaved and often treated with a factory-applied hydrophobic coating.
• Freeze-Thaw Resistance: In colder climates, the board must withstand hundreds of cycles without delaminating or cracking.

3. Pressure & Vibration Resistance

The “piston effect” caused by high-speed trains or heavy trucks creates significant positive and negative air pressure.

• Mechanical Strength: The boards are typically thicker (often 12mm to 20mm) and denser than residential siding.
• Fixing Systems: They are usually installed on high-grade stainless steel (316L) sub-frames to prevent galvanic corrosion.

• Common Comparison: Fiber Cement vs. MgO for Tunnels