Microwave absorption and mechanical properties of double-layer cement-based composites containing different replacement levels of fly ash

Abstract Double-layer absorbing cement-based composites with the thickness of 10 mm were prepared, including different replacement levels of fly ash (FA) in the absorbing layer as well as the matching layer for impedance matching. Waste polyethylene terephthalate bottle fragment was introduced as electromagnetic transparent reinforcement aggregate. Carbon black was used to be original absorbent in the absorbing layer. The microstructure and electromagnetic parameters of FA were closely looked at through scanning electron microscope, X-ray diffraction, and analyzer of vector network. The absorption and mechanical properties of cement-based composites were tested. It turned out that when the optimal replacement ratio of FA in the absorbing layer and matching layer gets to 50%:30%, the minimum value of reflection loss achieves −22.3 dB at 13.2 GHz; also, the value of absorption bandwidth that is effective (<−8 dB) is 6.4 GHz. Ni-Zn ferrite proves to be a feasible absorbent that is additional for the matching layer compared to what is added to the absorbing layer. The compressive strength of all the mixtures decreased, while the flexural strength decreased first and then increased with the rise of the FA replacement level.