Extruded cellular fly ash construction materials

Class C and Class F fly ashes were evaluated as candidates for the major component of low cost, low density, high strength ceramics suitable for construction use. The main objectives of this research were to: establish that strength reduction is linear with extruded cellular void fraction, develop low temperature processing of fly ash, and develop processing of thin-walled cellular bodies from fly ash. The scope of research included the development of processing procedures to produce the desired strengths and strength-to-density ratios (SDR), and to design dies to extrude honeycombs with a desired bulk density.;The bulk compressive strength for a honeycomb shape was empirically modeled as a function of the bulk and wall densities. It was assumed that the macrostructural incorporation of large, continuous channels along the extrusion axis would reduce the compressive strength (measured parallel to the extrusion axis) linearly. This is in contrast to the normally observed exponential decrease for ceramics with random microstructural porosity. This approach allows prediction of the wall density needed to attain a desired bulk density-strength combination. Conversely, experimentally attained densities can be used to design a die to extrude honeycombs having the desired bulk density and compressive strength. The wall density determines the solid area fraction that, after correction for any specific volume changes caused by densification or formation of reaction products, can be used to design the appropriate die.;Bulk densities and crushing strengths of honeycomb samples consolidated by sintering and by autoclaving were studied as a function of their respective compositions and processing conditions. Typical bulk densities, crushing strengths, and SDR obtained were 1.13 g/cm...