Alkali-activated fly ash foams - synthesis, chemo-physical properties and microstructure modeling

摘要

Inorganic foams offer several unique properties such as low thermal conductivity, fire resistance, or UV stability. Inorganic foam specimens were synthesized from fly ash and aluminium powder through an alkali-activation process. Depending on mix proportions, bulk densities ranged between 400 and 800 kg/m~3. Thermal treatment at 80°C for 12 hours accelerated curing process. Compressive strength was found in the range 4.5-9.0 MPa, flexural strength 0.6-1.7 MPa, Young's modulus 0.6-1.1 GPa, thermal conductivity 0.14-0.16 W/m/K and thermal capacity around 1100 J/kg/K. Exposing the foams to temperature 800°C led to a small decrease of compressive strength while exposure to 1100°C sintered the foam to higher strength of 13 MPa. Volumetric shrinkage 20% occurred at 1100°C without further disintegration. Residual compressive strength was determined after exposure to NaCl, HC1, Na2SO4, MgSO4, H2SO4. The highest reduction to 20% occured in both acids with pH=2 after one year of exposition. Digitized microstructures entered finite element analysis to validate a stress-strain diagram.