Open Access Library Journal How to cite this paper: Sakkas, K., Kapelari, S., Panias, D., Nomikos, P. and Sofianos, A. (2014) Fire Resistant K-Based Metakaolin Geopolymer for Passive Fire Protection of Concrete Tunnel Linings. Open Access Library Journal, 1: e806. http://dx.doi.org/10.4236/oalib.1100806 Fire Resistant K-Based Metakaolin Geopolymer for Passive Fire Protection of Concrete Tunnel Linings Konstantinos Sakkas 1,2 , Stergiani Kapelari 1 , Dimitrios Panias 1 , Pavlos Nomikos 2 , Alexandros Sofianos 2 1 Laboratory of Metallurgy, School of Mining and Metallurgical Engineering, National Technical University of Athens, Athens, Greece 2 Laboratory of Tunnelling, School of Mining and Metallurgical Engineering, National Technical University of Athens, Athens, Greece Email: sakkas@metal.ntua.gr Received 27 June 2014; revised 31 July 2014; accepted 7 September 2014 Copyright © 2014 by authors and OALib. This work is licensed under the Creative Commons Attribution International License (CC BY). http://creativecommons.org/licenses/by/4.0/ Abstract A fire resistant metakaolin geopolymer is developed and its performance under thermal loading is examined in this paper. The geopolymer was prepared by mixing metakaolin, doped with solid SiO2, with a highly alkaline potassium hydroxide aqueous phase in order to create a paste that was subsequently cured at 70˚C for a certain period of time. The addition of solid SiO2 was important in order the geopolymer developed to be fire resistant for temperatures up to 1350˚C. The mechani- cal, physical and thermal properties of the metakaolin geopolymer were measured and compared with available commercial fire resistant materials. The behavior of the metakaolin geopolymer upon exposure on fire was studied following the EFNARC guidelines for testing of passive fire pro- tection for concrete tunnels linings. The geopolymer was subjected to the most severe fire sce- nario, the Rijks Water Staat (RWS) temperature-time curve. During the test, the temperature in the geopolymer/concrete interface remained under 220˚C, which is 160˚C lower than the RWS test requirement, proving the ability of material to work successfully as an efficient thermal barrier. After the test the surface of the geopolymer had exfoliated and cracked, without losing its struc- tural integrity. Thus, the concrete slab protected by the geopolymer did not appear any form of spalling or degradation of its compressive strength. Keywords Metakaolin, Geopolymer, Tunnel Linings, Passive Fire Protection Subject Areas: Composite Material, Inorganic Chemistry, Material Experiment