(570a) Understanding the Synthesis, Structure and Durability of Fly Ash Geopolymers

The activation of coal fly ash by alkaline hydroxide and/or silicate solutions leads to the formation of a class of materials known as ?geopolymers.' These materials have been proposed as an alternative to Portland cement to reduce the currently very high worldwide CO₂ emissions due to concrete manufacture. However, for the commercial utilization of this technology to succeed, a fuller understanding of their intrinsic physicochemical properties is required. Recent work has focused on the analysis of the synthesis mechanisms, nanostructure, microstructure and chemical durability of the primary binder phase within geopolymers, which has generally been identified as an X-ray amorphous, nano- to meso-porous aluminosilicate gel. This presentation draws together data from a wide range of analytical techniques to present a detailed overview of the current state of the art in the understanding of fly ash geopolymers. Infrared spectroscopy, diffractometry, microscopy, thermal analysis and porosimetry are all able to provide key information, enabling researchers to ?piece together' the details of geopolymer structure and performance on length scales ranging from nanometers to centimeters. In addition, the use of 'model systems' - systems with simpler chemistry but similar synthesis pathways - also provides valuable information regarding reaction mechanisms during geopolymer formation. The most commonly studied model system is the reaction between alkali silicate solutions and metakaolin (calcined kaolinite clay), and some recent key insights obtained from this system will also be discussed.