The thermal conductivity mechanism of sewage sludge ash lightweight materials

The foaming reactions and the hydration and Pozzolanic effects of processed sewage sludge ash (SSA) allow it to be used as the main ingredient to make lightweight materials. The thermal conductivity of the SSA lightweight materials (SSALM), the SSA properties and how the mixing ratio of the materials influences the heat insulation properties are investigated. The results show that the thermal conductivity of SSA is low. When at room temperature, the pores in the specimens are filled with air, hence, the thermal conduction modes of these materials will be solid or air conduction. Radiant thermal conduction and natural convection can be ignored. The characteristics of the porosity, irregular particles and lightweight after the foaming reaction lead the thermal conductivity of the SSALM low to be 0.0763-0.2474 W/m K. When the water-to-solid ratio (W/S) and the amount of aluminum powder are increased, open and connected pores are formed, which negatively affects the compressive strength and the thermal conductivity. In addition, the total pore volume and thermal conductivity of SSALM are inversely proportional.