Using a vermiculite-based fire protection mortar to increase the fire resistance of reinforced concrete tunnels

The mechanical properties of reinforced concrete elements tend to be damaged and weakened after they have been exposed to a significant fire, leading to a thinner alkaline protective coating around steel reinforcement, as well as a reduction in the yield and stiffness of the steel. In tunnels, fire can increase the concrete temperature extremely rapidly, as the heat generated cannot escape, resulting in high vapor pressures within the concrete structure, which in turn leads to explosive spalling and a significant loss of strength, potentially endangering human lives. In this study a series of experiments was conducted to evaluate the performance of a specific lightweight fireproofing material in terms of its behavior in fire. Test specimens were produced and tested in accordance with exposure under the RWS fire curve up to a temperature of 1,350 °C as outlined in EFNARC guidelines, then the passive protection provided by the product was evaluated for various layer thicknesses and exposure times. To further substantiate these laboratory findings, a full-scale field test was carried out in an existing reinforced concrete tunnel (Panagopoula twin railway tunnel). The results further contributed to defining and evaluating the parameters in up-scaling this performance under real field conditions, and its influence as a realistic intervention scenario during tunnel service operations.