18 TH INTERNATIONAL CONFERENCE ON COMPOSITE MATERIALS 1 Introduction Geopolymer is an amorphous alumino-silicate material. Its structure is silicon and aluminium atoms bonding together by sharing oxygen atoms. Once the alumino-silicate powder was mixed with alkaline solution, a paste formed and transformed to hard material and gained strength [1]. Geopolymer was applied in many fields such as a replacement of Portland cement because its production lower energy and does not release the green house gases and use in building and mortar applications because of their short time strength development [2-4]. Geopolymer was prepared by dissolution of raw materials which have silica and alumina such as metakaolin and fly ash in alkaline solution [5]. In this study, geopolymer were prepared by using fly ash from power plant in Thailand as a raw material and the proportion of H 2 O and Na 2 O was varied to study their effect. Furthermore, the use of rice husk ash (RHA), by product from agriculture was studied to test possibility for apply as a replacement of fly ash 2 Experimental procedures 2.1 Raw materials and mixture compositions Fly ash, rice husk ash and sodium hydroxide (NaOH) were used as raw materials. The fly ash used was supplied by Mae Moh power plant in Lampang, Thailand. Its chemical analysis demonstrated that the fly ash was composed of SiO 2 , Al 2 O 3 , Fe 2 O 3 and CaO as the major component [5, 6]. Rice husk ash was obtained by burning the rice husk at 600 ๐ C for 2h in an electric furnace. The obtained rice husk ash was amorphous phase which was confirmed by XRD. Two series of mixtures were used in this experiment. In the first series, the mixtures was prepared by mixing fly ash and NaOH with varying the H 2 O and Na 2 O mol ratio in order to investigate the effect of H 2 O and Na 2 O on the properties of geopolymer. The compositions of the mixtures in this series are shown in Table1. For the second series, some amount of fly ash was replaced by rice husk ash. The amount of rice husk ash silica was varied from 5-15 wt% as the compositions shown in Table2. PREPARATION OF GEOPOLYMER USING FLY ASH AND RICE HUSK SILICA AS RAW MATERIALS P. Chaiyapoom 1,2 , S. Jiemsirilers 1,2* , S. Wada 1,2 , K. Hemra 3 , P. Thavorniti 3 1 Research Unit of Advanced Ceramics, Department of Materials Science, Faculty of Science, Chulalongkorn University, Bangkok, Thailand, 2 National Center for Petroleum, Petrochemicals and Advanced Materials, Chulalongkorn University, Bangkok, Thailand, (sirithan.j@chula.ac.th ) 3 National Metal and Materials Technology Center, Klong Luang, Pathumthani, Thailand Keywords: Geopolymer, fly ash, silica, Al-waste Abstract: Fly ash was used as raw material for making geopolymer. The samples were prepared by mixing fly ash and activator: sodium hydroxide (NaOH) with varying the proportion of H 2 O and Na 2 O. In addition, the possibility of using rice husk ash (RHA) as a partial replacement for fly ash raw material was studied. After mixing, the mixtures were casted in a plastic mold and left to harden for 48 hr at room temperature and 60 ๐ C and further cured for 7 days. The existing phases were investigated by using XRD. Bending strength and density of the geopolymers were also examined. Results showed that the amount of H 2 O and Na 2 O in the mixtures had an effect on the properties of geopolymer. The strength decreased with an increase in H 2 O mol ratio and the appropriate mol ratio of Na 2 O was 1.0. The addition of RHA as a silica source also had an effect on the strength of geopolymer. The strength increased with an increase in silica content.