Structure, Design and Applications of Geopolymeric Materials Ioanna Giannopoulou 1,a and Dimitrios Panias 1,b 1 National Technical University of Athens, School of Mining and Metallurgical Engineering, Laboratory of Metallurgy, 9 Heroon Polytechniou str., Zografos Campus, 15780, Athens – Greece. a mmmpgi@central.ntua.gr, b panias@metal.ntua.gr Keywords: Geopolymerization, Inorganic Polymers Abstract. The term “geopolymer” was firstly applied to describe a family of alkaline aluminosilicate binders formed by the alkali activation of aluminosilicate minerals. The formation of geopolymeric materials is the result of a complicated heterogeneous chemical reaction occurring between Al-Si solid materials and strongly alkaline silicate solutions. The geopolymerization reaction is exothermic and takes place under atmospheric pressure at temperatures below 100 o C. Despite of the intense research on the geopolymerization of different aluminosilicate materials and the development of a wide range of geopolymeric materials, the exact mechanism that takes place during geopolymerization is not fully understood. The most proposed mechanism for geopolymerization includes the following four stages, which proceed in parallel and thus, it is impossible to be distinguished: (i) Dissolution of Si and Al from the solid aluminosilicate materials in the strongly alkaline aqueous solution. (ii) Formation of Si and / or Si-Al oligomers in the aqueous phase. (iii) Polycondensation of the oligomers to form a three-dimensional aluminosilicate framework. (iv) Bonding of the solid particles into the geopolymeric framework and hardening of the whole system into a final solid polymeric structure. This paper will describe in detail the structure of the geopeolymeric materials, the parameters that has to be taken into consideration for their designing and their potential applications. Introduction Geopolymers is a new family of synthetic aluminosilicate materials formed by alkali activation of solid aluminosilicate raw materials [1]. The term “alkali activation” refers to the chemical dissolution of aluminosilicate raw materials in a strongly alkaline environment caused by an aqueous solution of sodium or potassium hydroxide. Geopolymers belong to the family of inorganic polymers, which are macromolecules linked by covalent bonds and having -Si-O-M-O- backbone, where M denotes principally aluminum and secondarily other metals such as iron [1,2]. The difference between geopolymers and the other inorganic polymers lies in the kind of silicon and aluminum precursors used for their synthesis. Normal inorganic polymers are synthesized with the sol – gel process, which employs silicon and aluminum alkoxides in alcohol–water solution as precursors. In such systems the alkoxide groups are removed stepwise by hydrolysis under acidic or basic catalysis and replaced by hydroxyl groups, which then form -M-O-M- linkages, where M denotes Si or Al. Thus, branched polymeric chains grow and interconnect and through the gelation process form a network that spans the entire solution volume. Inorganic polymers, such as Poly(aluminosiloxanes), are polymers containing an -Si-O-Al-O- backbone synthesized by the sodium salt of a poly(dimethylsiloxane) and aluminium chloride as Si and Al precursors, respectively. Geopolymers, on the other hand, are synthesized by alkali activation of solid aluminosilicate raw materials utilizing as activator a strong alkaline aqueous solution of sodium or potassium silicate and sodium or potassium hydroxide [3]. In this case the Si precursor is the sodium or potassium silicate solution as well as the dissolved silicon from the aluminosilicate raw