Assessment Methods of Fire Damages in Concrete Tunnel Linings

The assessment of fire damage in concrete structures is a complex but intriguing task involving different areas of expertise, from Material Science to Structural Design, from Non-Destructive Testing to Fire Engineering. The problem grows to be even more challenging in the case of tunnels, as a consequence of the high fire severity and the operational difficulties implied by this type of infrastructure, but also because of the pressing time restrictions due to the high cost of traffic disruption during the assessment and repair works. A general overview on this subject is given in the paper, pointing out the different scales of observation, the relevant clues to be analysed at each scale and their appropriate inspection tools. These latter comprise a wide range of investigation techniques of different reliability and cost, but not many of them turn out to be viable and convenient to tackle the problem in question. In this perspective, some innovative assessment methods have been developed in recent years, having in common the ability to reveal the layered structure of fire damaged concrete, the relatively fast and easy implementation and the immediate availability of the results. A brief account on the features and the limitations of these methods is given also, as a tentative to trace some directions for future advances in this important and still open issue.