The effects of the passive fire protection layer on the behavior of concrete tunnel linings: A field fire testing study

The concrete tunnel lining behavior when exposed to a natural fire loading is very important for the designing of tunnel lining safety. This work presents details of field tunnel fire testing of concrete tunnel linings with and without the fire resistant coatings under a real and natural tunnel fire loading designed using the heat release rate (HRR). This test aims to develop a better understanding of concrete lining behaviors and the effects of the fire resistant coating when exposed to such a fire, rather than the standard temperature-time curves in a furnace as described in most past studies. The results of concrete spalling are shown on both the vault and spandrel areas with a total area of approximate 0.8 m2 and a maximum depth of 10 mm for concrete lining without the fire resistant coating. The underlying concrete maintains its original nature but with complete failure of the fire resistant coating after the fire as for the concrete lining with the fire resistant coating. The lowest concrete facial strength ratio normalized by the initial average value is 95.2% and 78.9% on the right spandrel, respectively, for concrete lining with and without the fire resistant coating. The smoke and the concrete lining temperatures were also measured. The highest average smoke temperature of 675 °C for the case with the fire resistant coating is higher than the 600 °C for the other case at a same experimental condition but different environments. The concrete temperatures for lining without the fire resistant coating are slightly higher than those for lining with the fire resistant coating. The concrete tunnel lining with the fire resistant coating shows a crucial and strong thermal hysteresis nature, and is useful in avoiding a fast and severe temperature rise, as well as potential spalling. The concrete lining without the fire resistant coating has only slight damage in this test. As a result, the fire resistant coating is not believed to be necessary for a natural tunnel fire with the HRR lower than this test. The results are also expected to a useful complement to concrete tunnel lining fire data.