Robotic Application of a 50 mm Thick Sprayed Concrete Fireproofing Layer

Fire is one of the most serious risks to a tunnel. The nature of tunnels—being long enclosed spaces—can increase the intensity of a fire, and make fire-fighting and rescue operations difficult. The damage that can be caused has been demonstrated by a number of historic tunnel fires, such as the Channel Tunnel fires of 1996 and 2008, and the Mont Blanc Tunnel fire in 1999.

Without any intervention, the high temperatures in a fire create thermal stresses and a build-up of vapour pressure within the pores of concrete, which eventually exceed the tensile strength and trigger explosive spalling. Spalling exposes the core of the section to severe temperatures, leading to a loss of concrete and steel reinforcement strength or further spalling of successive layers. The concrete used in tunnel linings is particularly susceptible to explosive spalling, due to its low permeability achieved by the addition of microsilica.^[1]