Why Type X fire boards are crucial for fire protection systems for tunnels?

European Assessment Document, EAD 350142-00-1106, based on ETAG 018 Part 4, defines fire protective products like boards for enhancing the fire resistance of load-bearing elements (e.g., concrete) or assemblies.

Climatic categories range from Type Z2 (internal dry use only) to Type X (unrestricted exposure).
Type X requires products to endure full weather exposure—rain, UV, freeze/thaw cycles, and humidity—while maintaining essential characteristics like fire resistance (Class A1 per EN 13501-1), mechanical stability, and durability over a working life of at least 25 years.
AESTUVER Tx, a cement-bonded, glass fibre-reinforced lightweight concrete board meets these demands explicitly. The ETA specifies:

- For thicknesses from 20 mm to less than 60 mm (and 60 mm), it achieves Type X for all uses, provided permanent moisture penetration is prevented (e.g., natural ventilation, lack of standing water).

- It complies with use categories 1–10 in ETAG 018-1, including protection of load-bearing concrete elements (Type 3), which is directly relevant to tunnel linings.

- Key performances include non-combustible reaction to fire (A1), water impermeability (per EN 12467, Clause 5.4.5), and bending strength (minimum modulus of rupture of 1.5 MPa in wet conditions).
 
This classification is verified through component-specific assessments, including durability tests under EN 12467 for resistance to water deterioration, soak/dry cycles, freeze/thaw, and heat/rain. The board's design and mineral composition ensure it retains integrity in exposed conditions, with no essential changes in fire-protective properties expected.

Practical examples include:
- Cladding for Tunnel Linings: Installed as direct or independent cladding on concrete slabs/walls, AESTUVER Tx prevents thermal damage, as seen in projects like German road tunnels where it's used for retrofits and new builds. Its abrasion resistance handles cleaning cycles and hits from stones and pebbles.

- Frost and Water Resilience: In numerous countries with snow falls and negative temperatures, where winter road salts are applied and ice forms, the board's Type X status ensures it withstands de-icing chemicals without degradation—critical for maintaining performance for the design life.

- Ventilation and Smoke Control: As part of fire-separating assemblies (use category 8), it contributes to compartmentalization, limiting fire spread in long tunnels.
 
Industry sources confirm its tunnel-specific design: AESTUVER Tx achieves "the best classification for weather, frost, and water resistance with Type-X," making it suitable for underground transport systems where moisture and temperature extremes are routine.

Durability is the cornerstone of Type X fire boards, assessed via extended methods in EAD Clause 2.2.2.4 (25-year working life) and EN 12467. These tests simulate accelerated aging, ensuring the board's performance (e.g., fire resistance, adhesion) holds under exposure. AESTUVER Tx passed all: resistance to water (Clause 7.3.5), soak/dry (7.3.6), freeze/thaw (7.4.1), and heat/rain (7.4.2), with no cracks, delamination, or strength loss affecting use.

 
These protocols mirror tunnel realities through controlled extremes:

- Freeze/Thaw Testing (EN 12467, Clause 7.4.1): Boards undergo 100 cycles of freezing (-20°C) and thawing in water, assessing strength retention (ratio RL). In tunnels, this reflects winter conditions where water seeps in, freezes, and expands—potentially cracking weaker materials. Real-life example: Numerous tunnels experience sub-zero temps  with meltwater; AESTUVER Tx's passing ensures no spalling or loss of fire protection, as proven in installations where boards endured 10+ years without failure.

- Heat/Rain Cycles (Clause 7.4.2): 80 cycles of heating (to 70°C) followed by water spraying simulate humid, hot environments. Tunnels often see heat from traffic (up to 50°C locally) combined with rain ingress at portals or leaks. This test reflects scenarios like summer heatwaves in hot climates, where moisture from vehicle wash or condensation cycles with drying; the board's resistance prevents warping and allows for maintaining tight joints.

- Soak/Dry Resistance (Clause 7.3.6): 50 cycles of immersion and drying measure dimensional stability. In urban tunnels like those in London or Paris, frequent cleaning with water jets or humidity from poor ventilation causes wetting/drying stress.

AESTUVER Tx's ensures the performance of fire protection systems for tunnels with no shrinkage (up to -0.25 mm/m at low humidity), preventing gaps that could allow fire penetration—mirroring real cases where untreated concrete degrades from cyclic moisture.

- Water Deterioration (Clause 7.3.5): Full immersion tests impermeability, with no water drops through the board. Tunnels face constant dampness from groundwater; this equates to scenarios in tunnels under rivers or seabed (e.g., Tyne Tunnel in Newcastle or Tuen Mun Chek Lap Kok Tunnel in Hong Kong) where water erodes materials. The board's "resistant" rating (per ETA) has held in field applications, with no reported moisture-induced failures over 25 years.
 
These tests, conducted under AVCP System 1 (third-party certification), provide a safety margin: accelerated conditions exceed typical tunnel exposures, ensuring longevity.