Effect of nano- and micron-materials on the thermal properties behavior in wet environments and heat transfer mechanism of foam concrete

Foamed concrete is a lightweight material with low thermal conductivity, widely used in civil engineering. However, its insulation performance slightly underperforms compared to organic insulation materials, while its porous structure results in poor impermeability and high moisture content, further affecting its thermal conductivity in wet environments. To improve the properties of foamed concrete, we incorporated aerogels (AG), hollow glass microspheres (HGM), and nano-silica (NS) in foamed concrete and adopted an orthogonal test to find the optimal behavior. The results show that adding 4 % AG reduced the moisture content of foamed concrete in a wet saturated state by 17.4 %, while the thermal conductivity in a dry state was reduced by 44.29 % and that in a wet saturated state was reduced by 18.1 %. On the other side, the addition of 4 % HGM also reduced the moisture content in a wet saturated state by 18.4 %, while the thermal conductivity in a dry state and a wet saturated state decreased by 17.13 % and 18.07 %, respectively. In contrast, although the addition of 4 % NS decreased the moisture content in a wet saturated state by 5.2 %, the thermal conductivity in a dry state and a wet saturated state increased by 17.83 % and 5.3 %, respectively. The effect of these nano- and micro-materials on the density of foamed concrete was analyzed, and an equation fitting the relationship between the moisture content and thermal conductivity was determined. We applied X-ray diffraction (XRD) and scanning electron microscopy (SEM) to better understand the relations between the microstructure and properties of the synthesized materials. Finally, the effect of these additives on the heat transfer mechanism in foamed concrete was discussed.