Sustainable PET-POFA composite bricks for microwave absorption application

The integration of smart building technologies and the associated microwave radiation exposure highlights the need for sustainable and effective absorbent materials in construction. This study investigates the fabrication and electromagnetic characterization of composite bricks developed from polyethylene terephthalate (PET) plastic waste and palm oil fuel ash (POFA), targeting dual functionality in structural performance and microwave absorption. Bricks were produced with varying PET contents (5%, 10%, and 20%) as an aggregate replacement, and the selected composite contained 10% POFA. After a standard curing process of 28 days, all samples were evaluated for microwave absorption using the NRL Free Space Arch method in the frequency range of 1 to 12 GHz, in both horizontal (6 cm thick) and vertical (10 cm thick) representing the orientations for brick installation. The results showed that PET-modified bricks (P5, P10, P20) achieved significantly higher microwave absorption compared to conventional commercial bricks, and the addition of POFA further enhanced the absorption performance, with the P10F10 composite achieving an absorption peak of -49.65 dB in the S-band. The vertical orientation intensifies the absorption in all developed bricks, as indicated by the maximum absorption of the P20 brick of -35.58 dB in the X-band. Material property analysis showed PET increased electrical resistivity and dielectric permittivity, whereas POFA addition reduced permittivity and moderate resistivity, thereby optimizing impedance matching and dissipative losses. These findings demonstrate a promising approach to sustainable construction, leveraging waste-derived materials for high-performance microwave absorbers that support both environmental and technological demands in modern buildings.