I. NIKOLIĆ et al ... GEOPOLYMERIZATION OF FLY ASH AS A POSSIBLE SOLUTION … ZAŠTITA MATERIJALA 53 (2012) broj 4 361 IRENA NIKOLIĆ 1 , RADOMIR ZEJAK 2 , Scientific paper DRAGOLJUB BLEČIĆ 1 , MILENA TADIĆ 1 , UDC:504.3.056 VELIMIR R. RADMILOVIĆ 3 Geopolymerization of fly ash as a possible solution for stabilization of used sandblasting grit Geopolymers are relatively new, environmentally friendly and light weight materials which form as a result of a reaction of aluminosilicate materials with a highly alkaline solution. They are characterised by good mechanical properties and are considered a possible replacement for ordinary Portland cement in construction. In addition, geopolymerization technology is recognized as a possible way of immobilization of toxic waste (nuclear waste, waste water, waste containing heavy metals, etc.). In this paper, we have investigated the possibility of immobilization of used sandblasting grit in fly ash based geopolymers. The results have shown that geopolymerization of fly ash with the addition of used sandblasting grit is possible. Microstructure of synthesized geopolymers is characterised by the presence of aluminosilicate gel and unreacted fly ash. However, compared to fly ash based geopolymers, lower compressive strength is obtained. It is demonstrated that Si/Al ratio determines the compressive strength of geopolymers. Key words: geopolymerisation, geopolymer, fly ash, sanblasting grit. 1. INTRODUCTION Fly ash is a coal fire by-product material from coal fired power stations. The total amount of coal combustion product produced worldwide is estimated to be about 550 million tonnes, about 68 % of which is from fly ash, and about 117 millions of tonnes of fly ash is valorized into the construction industry and underground mining during 2008. year [1]. Fly ash has already been applied in the civil engineering as an additive to the cement, as raw kiln feed material and as a direct cement replacement, in concrete, in the production of lightweight aggregates and lightweight blocks and road construction. In addition of red mud, steel slag and used sandblasting grit, fly ash landfill in Pljevlja is indentified as a major environmental problem in Montenegro. It is estimated that about 44 t/h of fly ash is produced in coal fired power station Pljevlja [2], so its valorisation deserves special attention. In recent years, intense studies of the geopolymerization process as an option of fly ash utilisation were studied extensively. Glukhovsky first hypothesized that natural geological transformation which occurs in aluminosilicate minerals may be the basis of structure formation process in a cementitious binder 3. Later, Davidovits 4 suggested that a reaction of solid. Author's address: 1 University of Montenegro, Faculty of Metallurgy and Technology, Dž. Vasingtona bb, Podgo- rica, Montenegro, 2 University of Montenegro, Faculty of Civil Engineering, Dž. Vašingtona bb, Podgorica, Monte- negro, 3 University of Belgrade, Faculty of Technology and Metallurgy, Karnegijeva 4, Belgrade, Serbia Paper received: 12.05.2012. aluminosilicate minerals with strong alkali metal silicate solutions be called “geopolymerization” and useful, environmentally friendly materials produced in such a way - “geopolymers” or inorganic polymers. Raw materials for the synthesis of geopolymers can be either natural aluminosilicate minerals 5,6, or waste with high content of SiO 2 and Al 2 O 3 ,such as fly ash and metallurgical slag 7,8. In the pastten years geopolymers attracted much attention primarily due to good mechanical properties. The geopolymeri- zation mechanism has not yet been clarified and it is assumed that it consists of several steps 9:  Dissolution of solid aluminosilicate materials in a strong alkaline aqueous solution  Formation of Si and/or Si–Al oligomers in an aqueous phase  Polycondensation of oligomeric species or units in an aqueous phase to form an inorganic polymeric material  Bonding of undissolved solid particles in the final geopolymeric structure. Besides, geopolymerization is recognized as a possible technology for immobilization of hazardous waste 10. In that sense we have investigated the possibility of immobilization of used sandblasting grit through the geopolymerization process. Sandblasting grit is used in shipyards to clean dirt, corrosion, paint or other coatings from ship surfaces and, as a result, it contains organic and inorganic toxic components which may represent an important problem in the environment protection policy.