SYNTHESIS AND CHARACTERIZATION OF METAKAOLIN BASED GEOPOLYMER FROM NARATHIWAT AND PRACHIN CLAYS

Abstract

Geopolymers are a new type of CaO-free inorganic alumino-silicate cementitious material, which have been developed as an alternative material to replace Portland cement. Geopolymers, are three dimensional structure, have excellent properties and high performance such as higher resistance to acid and fire, long-term durability, low shrinkage and low permeability, etc. Metakaolin based geopolymers were synthesized by using kaolin from Narathiwat and Prachinburi provinces, Thailand as starting materials. The purposes of this research were to investigate the optimum conditions of geopolymers which give good properties. Raw materials were characterized by X-ray diffraction (XRD), Differential Thermal Analysis (DTA) and Particle size distribution. Metakaolins were obtained by calcination of Narathiwat and Prachinburi kaolins. The calcined temperature was 650°C and soaked for 6 h. in order to allow kaolinite transformed to metakaolinite completely then they were analyzed by XRF for chemical compositions which was calculated to mix the raw materials with alkali solutions. The obtained metakaolin was mixed with strong alkaline solution until homogeneous with the different conditions which were concentrations of sodium hydroxide (NaOH), Si/Al ratios, curing temperatures and curing time. Narathiwat and Prachinburi geopolymers were characterized by XRD, SEM, FTIR, Compressive strength, Bulk density, Water absorption and Apparent porosity. XRD pattern showed that metakaolinite phases were change to were more amorphous phase. The best concentration for this study was 12 M of NaOH which gave the highest compressive strength with the Si/Al ratio of Narathiwat and Prachinburi geopolymers were 1.49 and 2.52, respectively. The optimum curing time was 28 days at ambient temperature, since the geopolymerization occurred slowly at room temperature. The FTIR spectra could confirm the developed geopolymeric structure.