Fire resistant behavior of newly developed bottom-ash-based cementitious coating applied concrete tunnel lining under RABT fire loading

When tunnels are exposed to prolonged fires, they are likely to suffer heavy damage and partial collapse. Because of the difficulties involved in repairing tunnels damaged by fire, the application of fire protection coatings as a preventive measure has been widely used. The application of such coatings is a relatively simple construction method that is effective in protecting tunnel structures from collapse. However, the coating materials currently available are rather expensive and have low compressive and tensile strengths. Low strengths of coating materials can lead to fatigue failure and spalling of the tunnel linings, both during fire loading, due to internal evaporative pressure, and after fire loading, due to negative pressure from service traffic. This paper presents a newly developed fire-protection cementitious coating material, which can resist both fire and service traffic loadings. The newly developed coating material is low in cost and high in strength, qualities achieved by using bottom ash as the fine aggregate. Polypropylene fibers are used to release internal evaporative pressure via melting during thermal loading, providing a pass-through channel. The developed coating material is experimentally evaluated by means of static strength tests and RABT fire loading tests using an LPG furnace. The strength properties, failure mechanisms, and thermal protection study results for this material are discussed in detail.