An Experimental Study on the Fire Behavior of Concrete Segments in Tunnel Linings
As soon as the plan to build deep and long tunnels in Korea was announced, guaranteeing fire-resistance of R/C tunnel linings became an important issue. As a matter of fact, the R/C segments used in bored tunnels are structural members which are requested to resist both the transverse pressure of the soil and the longitudinal thrust of the TBM. Because of the temperature sensitivity of the high-performance concrete (compressive strength>40 MPa) that will be used, proper measures should be taken against possible fire-induced damage, like surface spalling and deterioration of the reinforcement. In the past, concrete linings were built in Korea with scanty attention to their fire safety, as demonstrated by the lack of studies on fire resistance of both materials and structures. Therefore, in this study the objective is how to improve the safety of R/C tunnel linings in case of fire, by comparing the damage observed in some full-scale tests recently performance in Korea with the damage observed in the tests performed by EFNARC (European Federation of Producer and Applicators of Specialist Products for Structures) and by investigating the fire behavior of a concrete lining as a whole.
Mechanical properties of various concrete after high temperature exposure Mechanical property of various types of concrete after high temperature exposure is investigated. Considering compressive strength requirement for a vertical element in high rise building, concrete specimens with various design strengths of 35, 80, 100, and 150 MPa were tested. Particularly, the influence of incorporated steel fiber on fire resistance is of interest in this study. Experimental results show that the fire resistance depends on the design strength and steel fiber content. Normal strength concrete (NSC) of a design strength of 35 MPa or high performance concrete (HPC) of 80-100 MPa does not spall when exposed to 100-400 °C of temperature. However, an explosive spalling occurs at 300 °C when the HPCs contain 1 vol.% of steel fiber. Ultra-high performance concrete (UHPC) of a design strength of 150 MPa and 1.5 vol.% of steel fiber also shows dramatic spalling at 300 °C. The experimental results found in this study can contribute to a better understanding of the behaviors of HPC and UHPC under fire and the role of steel fiber on the fire resistance.
