Numerical simulation of porosity on thermal properties and fire resistance of foamed concrete

Abstract

The relationship between thermal insulation properties and porosity of fly ash based foam concrete was built, in which effective density, effective heat conductivity, and effective specific heat of fly ash based foam concrete were deduced as functions of porosity. Using the model, the effective heat conductivity of density of 580 kg/m³ fly ash based foam concrete was the theoretically calculated as 0.145 W/(m K) while the experimental measured value was 0.142 W/(m K). The relative error of heat conductivity was very low at 2.1%. The effective specific heat within the model was 967.05 J/kg K and the experimental value was 920 J/kg K with a relative error of 5.1%. Then, the effective heat conductivity and specific heat models were incorporated into heat transferring model to calculate the temperature field of fly ash based foam concrete wall during a fire incident. Finally, the temperature field of fly ash based foam concrete wall and traditional dense concrete wall during fire incident were calculated and compared. Comparing the temperature field of the fly ash based foam concrete wall with the traditional concrete wall, it was found that at close to fire-side surface, the temperature in the fly ash based foam concrete wall could reach 1039 °C, while the lowest temperature in the fly ash based foam concrete wall remained at 20 °C for a thickness of 7 mm. In contrast, at close to fire side of surface, the temperature of traditional concrete wall was 987.2 °C at 360 s and the lowest temperature in the traditional wall was 102.9 °C at the opposite side-wall surface far away from the fire direction. As expected, the data demonstrated that the use of fly ash based foam concrete in wall construction adds greatly to the time for people to leave in safety.

Keywords:

• foam concrete
• porosity
• effective heat conductivity
• effective specific heat
• temperature field