EFFECT OF ALKALI CHOICE ON GEOPOLYMER PROPERTIES Waltrud M. Kriven and Jonathan L. Bell University of Illinois at Urbana Champaign 105 Materials Science and Engineering Blgd. 1304 W. Green St. Urbana, IL 61801 ABSTRACT A series of geopolymers were made using both KOH and NaOH alkaline solution by curing in an autoclave at 1000 psi and 80 o C, respectively, for 24 hours. Samples were made using only KOH or NaOH or some combination thereof. The resulting samples were tested using scanning electron microscopy (SEM), environmental scanning electron microscopy (ESEM), mercury intrusion porosimetry (MIP), and x-ray diffraction (XRD). The autoclave technique produced highly reacted, 0.25 in. diameter, cylindrical samples which were virtually free of macropores. A separate series of 1 in. diameter compression samples were made and tested after being cured at 40 o C for 24 hours. It was found that there may be a critical combination of KOH and NaOH that can be added to produce a highly dissolved and crossed linked sample. The multiple alkali sources can act in a synergistic fashion to create a sample of optimal properties. INTRODUCTION A geopolymer can be defined as the material that results from the geosynthesis of polymeric alumino-silicates and alkali-silicates, yielding a three-dimensional polymeric framework of linked SiO 4 and AlO 4 tetrahedra. 1  An aluminosilicate material such as kaolinite can be dissolved in an alkali-silicate solution to form a rock hard brittle ceramic. Using the proper chemistry, one can attain a high strength material that can set in a little as a few hours at room temperature. Geopolymer materials and geopolymer cement blends can be used for a number of applications such as fire and acid resistance, immobilization of heavy metals, bonding of metal and ceramic surfaces, and various structural materials. The alkali solution of choice both in research and industry is typically KOH or NaOH due to is performance, cost, and availability. Most studies examine the effect of using one or the other exclusively. The intention of the current study is to examine various properties of geopolymer samples prepared using KOH and NaOH exclusively, as well as in blends. EXPERIMENTAL METHODS All of the materials used to make the geopolymer cement in this study are listed in Table I. Alkali waterglass solutions were made by dissolving silica into the respective alkali solution according to the ratios given in Table 2. These ratios were chosen based on previous work, as it allows for optimal workability and strength. 2, 5, 7, 8 The waterglass solutions were aged for two weeks to ensure full dissolution of silica. Hydrite PXN clay was calcined at 700 o C for 1 hour in order to obtain metakaolin as confirmed by XRD. 2 This ensured a higher reactivity of clay in the waterglass. The metakaolin was then added to the waterglass solution and mixed for 15 min using a high shear mixer (IKA Labortechnik RW200ZM high shear mixer) and subsequently vibrated for 5 min. to remove entrapped air bubbles. Samples of the type listed in Table III were then poured into respective molds to either be autoclaved or prepared for compression testing.