Innovative multi-functional foamed concrete made from rice husk ash: thermal insulation and electromagnetic wave absorption

The casual disposal of rice husks leads to space occupation and environmental pollution. This study explored rice husk ash as a substitute for conventional materials to prepare novel multifunctional foam concrete. The mechanical properties of the foam concrete were characterized, and the samples' thermal conductivity and reflectance loss were tested using the heat flow meter method and coaxial transmission method to evaluate the insulation and electromagnetic absorption capabilities of the multifunctional foam concrete. The results indicate that the substitution of rice husk ash resulted in a decrease in compressive strength and flexural strength of the foam concrete. However, there was a particular enhancement in insulation and electromagnetic absorption capabilities. By alkaline activation and adjustment of the rice husk ash, the strength of the foam concrete showed an initial increase followed by a decrease with increasing alkaline content. When the rice husk ash content was 10%, and the alkaline content was 0.4wt.%, the thermal conductivity decreased to 0.139 W/(m·K), meeting industry standards. Adding 1wt.% of carbon fibers resulted in optimal electromagnetic absorption performance, with a minimum reflection loss of −19.7 dB. Furthermore, developing this new multifunctional foam concrete can bring substantial economic benefits and mitigate the emission of 10.09 kg of carbon dioxide per square meter of foam concrete wall produced.