Production Geopolymer Materials by Coal Fly Ash

Topics: Fly ash, Concrete, Coal Pages: 8 (2438 words) Published: October 17, 2010
Abstract : Coal ash is the main waste from power plant. It is estimated that the consumption of the coal for power plant will increase to 240 million tons each year and the coal ash wastes will produce more than 2 million tons per year. Although the utilization of coal fly ash can be reached 74.1%, large amount of coal fly ash and bottom ash still cannot be utilized. The purpose of this research is to develop a process to manufacture geopolymer using coal fly ash waste. The test results show that the characteristics of waste coal fly ash-based geopolymer have great physical/mechanical properties for fire resistance test. A 10 mm thick geopolymer panel was exposed to a 1100¢J flame, with the measured back-side temperatures reaching less than 470¢J after 30 minutes. The products can be fabricated for construction purposes and have great application potential. Keyword: coal fly ash, geopolymer, fire resistances

Throughout the world, the amount of coal fly ash from power plant is increasing. The production of coal fly ash from Tai-Power Company (TPC) is about two million tons per year and the quantity of fly ash is four times of bottom ash in Taiwan (Kuo, 1991 Kuo, 1994 ¡F ¡FLee et al., 1998¡FWang et al., 1996). For the purpose of energy, economic developing, and environmental ecosystem conserving, many research works and development investigations have been conducted in its utilizations as a starting material, such as using coal fly ash to produce artificial reef (Kuo, 1994), as an addition materials for concrete (Kuo, 1994; Lai, 1994¡FYang, 1997), raw materials of ceramic (Wang et al., 1994), etc. The reuse amount of fly ash is still limited. However, due to the coal fly ash in Taiwan is classified as Class F (Yen, 1996), and it could be a good raw material for making geopolymer. Geopolymers, an inorganic polymer, firstly developed by Joseph Davidovits in 1978 (Comrie and Davidovits, 1988; Davidovits et al., 1990), have been gradually attracting world attention as potentially revolutionary materials. It is a class of three-dimensionally networked alumino-silicate materials, similar to natural zeolite minerals. Unlike conventional organic polymers, glass, ceramic, or cement, geopolymers are non-combustible, heat-resistant, formed at low temperatures, and fire/acid resistant. The bond of geopolymer is chemical bonding the mechanism is different to cement hydration. While using fly ash as cement addition, between fly ash and Ca(OH)2 occurred during cement hydration, will appear secondary reaction, then forming hydrated materials (Ke, 1994). However, the geopolymerisation including the following step: (1) the dissolution of alumino-silicate oxide in MOH solution (M=Na or K); (2) the diffusion of dissolved Al and Si complexes, from particle surfaces to the interparticle space; (3) the formation of a gel phase resulting from the polymerization between an added silicate solution and Al and Si complexes; (4) hardening of the gel phase by the exclusion of spare water to form geopolymeric product (Xu et al., 2001). According to previous studies (Hua et al., 1999¡F Swanepoel et al., 2002), geopolymerisation involves a chemical reaction between various aluminosilicate oxides with silicates under highly alkaline conditions, which can be presented schematically as follow: + n(Si 2 2 + 2nSiO + NaOH/KOH ++ n(OH) -O -( H (1) O,Al) O Na ,K 3 -O ¡Ð -SiO)3 -Si -Al 25 O 2+ 4nH 2 (Si-Al materials) (OH) 2 (Geopolymer precusor)

+) ¡Ð + 4H (Na ,K -O-Si-O-) n(OH)¡Ð 3 -Si-O-Al +NaOH/KOH+ - (-Si-O-Al2 (2) O 3 -O-Si-(OH) OOO (OH) 2 (Geopolymer backbone) The aim of this research is to try to fabricate a coal fly ash-based geopolymer for fire -resistance purposes that has the potential for using coal fly ash in Taiwan.

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Table1. The composition of fly ash and metakaolinite Composition (Wt. %) SiO2 Al2 O3 Fe2 O3 CaO MgO Na 2 O K2 O TiO2 PbO ZnO Cr2 O3 1800 1600 1400

Fly ash 59.95 22.35 3.65 1.45 0.77 0.62 1.07 0.99 0.04...
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