Fire behaviour of tunnel concrete – Results of a DZSF research project

Abstract Fires in railway tunnels pose a considerable challenge to the integrity of the structures. The main objective of the research project "Structural fire protection in railway tunnels", funded by the German Centre for Railway Research (DZSF), is to experimentally investigate the fire behaviour of tunnel concrete under realistic conditions. The background to this includes new developments in concrete technology and the limited data available on the influence of these parameters on spalling. A cascading experimental approach was used for the analysis. The first step involved meso‐scale screening tests for the three main tunnel construction methods – shotcrete, segmental and cut and cover construction. Practical concrete mixes were used, some of which were taken directly from construction sites. These fire tests served to narrow down the relevant factors at the material level. In a second step, large‐scale fire tests were carried out on loaded test specimens to investigate the behaviour of the components. This article presents the test programme, the methodology used and initial observations on the behaviour of the concretes tested under fire conditions. The findings presented here represent an intermediate step and will be evaluated and developed in a further phase of the project.