Invited Talk: Geopolymerisation Using Coal Fly Ash and Wood Fly Ash with Internal and External Alkali Sources

Geopolymers offer several advantages over Ordinary Portland cement(OPC), especially in terms of environmental sustainability and physiochemical properties. Here geopolymers were formulated using coal fly ash with high iron oxide and calcium oxide contents and displayed improved heat resistance, but a relatively lowered acid resistance than conventional OPC. The costs of alkaline reagents used and the benefit of geopolymer selling were the major factors affecting the economic feasibility of geopolymer production. To further lower this cost incurred due to use of external alkaline reagents and to facilitate the recycling of more ash, a follow-up study using wood fly ash as the alternative source of alkaline activator for the geopolymerisation with coal fly ash was done. However, the leaching of heavy metals from the wood fly ash could potentially pose an environmental concern. Therefore, the focus of this study was to reduce the leachability of wood fly ash throughout the geopolymerisation process and to understand the effects of various factors on the leaching process. Our result showed that the dominant factor was the type of alkaline activator. By comparing the leaching data to the Denmark’s leaching criteria, the best performing geopolymer sample uses wood fly ash as its alkaline activator, thus doing away with any external alkaline source and reducing the overall cost.