Effect of temperature on the in-situ and post-heating residual strength of FRC tunnel segments by means of Simplified Barcelona test

Abstract

The occurrence of a fire into a tunnel lining can lead to tremendous losses and casualties. In the case of tunnels produced with reinforced concrete segments, even a short exposure time at moderate temperatures can lead to a severe degradation of the cementitious matrix and, in some cases, of the reinforcement. The occurrence of spalling is still more critical, given that it can evolve to a total collapse of the structure. The use of synthetic macrofibers helps to avoid cracking and spalling in tunnel segments. However, when subjected to elevated temperatures, causes losses in reinforcement capacity of segments. In this context, this project aims to investigate the effect of elevated temperatures on the mechanical behavior of FRC (fiber reinforced concretes) tunnel segments by means of Simplified Barcelona Tests. Samples extracted from the tunnel concrete segments will be tested after an exposure period of 1h at constant temperature in two different testing conditions: In-situ (hot condition) and residual (after cooling). Targeted constant temperatures considered will be in a range of 25°C to 600°C, in view of the main dehydration processes present in the Portland cement matrix. Thermogravimetry (TG) and X-ray diffraction (XRD) analysis will be used to study matrix phase changes as a function of temperature. Scanning electron microscopy (SEM) will be addressed in order to investigate the damage processes in the plain matrix and in the fiber-matrix interfaces. The results will be used through AES model to evaluate the possible reduction of the strength capacity of the tunnel segments. Such results will also provide important parameters for future designs of FRC tunnel segments in terms of structural safety, damage tolerance and maintenance.