Effect of elevated hot temperatures on hybrid geopolymer synthesized with coal fly and bottom ashes

H. Kim, C.W. Park
University of Seoul,

Keywords: geopolymer, coal ash mixture, alkali activator, high temperature, compressive strength, thermal conductivity, morphology


Ordinary Portland Cement (OPC) concrete has been most widely used for construction materials although the strength deterioration of OPC concrete in high temperature has been pointed out as its inherent flaw. Considering that fire is one of the hazards that attack buildings, however, OPC concrete does not seem to be suitable as durable building materials. One of the main reasons for the deformation of OPC concrete in elevated temperature is the thermal incompatibility between its aggregates. In contrast to OPC concrete, geopolymer cement is well known for its higher fire resistance due to its inorganic rigid. We have employed coal fly and bottom ash mixture containing heterogeneous particles having different shapes as a source material of so-called hybrid geopolymer. To investigate the thermal behaviors of the hybrid geopolymer subjected to high temperatures, we manufactured the geopolymer with coal fly (mean particle size=32.9 μm) and bottom (mean particle size = 206.7 μm) ash under alkali activator solution by replacing bottom ash contents up to 80 percent by weight of ash mixture. The geopolymer samples obtained were placed on a furnace and exposed to 300, 600 and 900 ℃. The changes in compressive strength, thermal conductivity and other morphologies were observed. Especially after exposed to 900 ℃, the geopolymer exhibited the highest values of compressive strength and thermal conductivity with changing its color gray to reddish. SEM and XRD showed that the geopolymer treated in 900 ℃ was sintered to bring about new crystalline phases of nepheline and anorthoclase which contributed to the strength improvement.