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Innovative materials for passive fire protection of tunnels
Abstract and Figures
An essential element of tunnel design is to ensure that the structural elements will not fail due to
the high temperatures, which may be developed during a fire. For this problem, three different methods
however there is always a need for developing a new material with improved fire resistance properties and
low cost. The geopolymerization technology seems to be very attractive in developing effective fire
resistant materials. So using a slag as a raw material,pure alumina and a highly alkaline solution a fire
resistant geopolymer was produced. The mechanical, physical and thermal properties of the produced
material were measured. Also the resistance under high temperatures (up to 1350 oC) according to
E.F.N.A.R.C specifications and guidelines was tested. From the tests results it is concluded that the
geopolymer perform well under severe fire scenario without yielding or spalling, according to the standard
fire temperature curves.
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Geopolymer Resins and Geopolymer Cements are new advanced mineral binders. In both cases, resins/binders and cements, the same green chemistry is used: geopolymerization. In industrialized countries, for geopolymer applications, emphasis was put on fire and heat resistance, and also in radioactive and toxic-waste management, yielding sophisticated geopolymer resins and binders: K-poly(sialate- siloxo), K-poly(sialate-disiloxo) systems, as well as K-nano-polysialate matrices. In emerging countries, the driving elements for sustainable development are Green-House and Global Warming concerns. The geopolymer green-chemistry generates new types of low-CO2 cements for building and infrastructure applications, based on geological as well as industrial waste-materials (coal fly-ashes, coal-mining waste, etc.). As a consequence, Geopolymer Concrete possesses physico-chemical properties entirely different from those of regular Portland-Cement-based concrete.
The design of a fire resistant coating for tunnel passive fire protection and its performance under thermal loading are presented. The material falls under the class of potassium based geopolymers (K-geopolymer) and was prepared by mixing ferronickel (FeNi) slag, doped with pure alumina, with a highly alkaline potassium hydroxide aqueous phase. The physical, mechanical and thermal properties of the K-geopolymer were determined and compared to those of some commercially available fire resistant materials. Its behavior upon exposure to fire was assessed by subjecting a concrete slab, coated with a 5 cm thick K-geopolymer layer, to thermal loading under the RijksWaterStaat (RWS) temperature–time curve, which is considered as the most severe prescribed tunnel fire scenario. During the test, the geopolymer/concrete interface temperature remained under 280 �C, which is 100 �C lower than the RWS test requirement, proving the effectiveness of the material as a thermal barrier. In addition, the K-geopolymer retained its structural integrity after the test, without any significant macroscopic damage.
In this paper the effect of the water, sodium hydroxide and sodium silicate contents in the synthesis of fly ash-based geopolymers on their compressive strength is investigated. X-ray diffractograms of geopolymers indicated the existence of the major crystalline phases of fly ash, as well as the formation of a new amorphous phase in the geopolymeric matrices. Fourier-transform infrared (FTIR) spectroscopy analysis revealed essential fly ash phase transformations within geopolymers that affected their mechanical strength. Compressive strength of the produced geopolymers is correlated with the role that the investigated parameters play in the geopolymerization process. The compressive strength is increased with the decrease of water content, as well as with the increase of sodium silicate in the synthesis of geopolymers. Concerning the sodium hydroxide content in the geopolymers synthesis compressive strength is observed to being optimized for a sodium hydroxide concentration in the aqueous phase equal to 6.6 M. In general, a compromise among the investigated parameters might lead to geopolymeric materials with a compressive strength higher than 40 MPa.
Nomikos P and Sofianos A 2014b Potassium based geopolymer for passive fire protection of concrete tunnels linings Tunnelling and Underground Space Technology 43
- K Sakkas
- D Panias
Sakkas K, Panias D, Nomikos P and Sofianos A 2014b Potassium based geopolymer for passive fire
protection of concrete tunnels linings Tunnelling and Underground Space Technology 43 148-56