Sludge-based carbon as an effective admixture in alkali-activated cementitious composites to shield electromagnetic radiation

Highlights

• Sludge-based strengthens the EMI shielding behavior of alkali-activated cementitious composites.
• Composite with 20 wt% of the functional admixture achieves 4220 dB/m across the X-band.
• The dominating shielding mechanism depends on the content of the functional admixture.
• Reduction in compressive strength and flexural strength with the functional admixture inclusion is noted.

Abstract

This study first utilizes pyrolyzed municipal sludge (PMS) to prepare waste-based alkali-activated cementitious composites (ACC) with enhanced electromagnetic interference (EMI) shielding properties. The effect of PMS content on the EMI shielding effectiveness of the ACC was systematically investigated. The PMS used in this study features an amorphous carbon structure and ion oxides, which contribute positively to the shielding performance. Both the real and imaginary components of permittivity increase with higher PMS content, indicating enhanced dielectric and conductive properties. When PMS content is below 12 wt%, absorption is the dominant shielding mechanism; however, reflection becomes dominant when the content exceeds 12 wt%. The skin depths of the ACC are smaller than the specimen thickness and decrease with increasing frequency, further enhancing EMI shielding effectiveness. The maximum total shielding effectiveness (SE_T) achieved was 20.8–25.3 dB over the X-band, approximately five times higher than ACC without PMS. Across all PMS content levels, absorption loss (SE_A) is the primary contributor to SE_T. The shielding mechanisms include conduction loss and polarization loss, such as defect-induced interfacial polarization, dipolar polarization, and molecular currents. This study discovers a new approach to using municipal sludge as an EMI shielding admixture and contributes to global sustainability in the construction industry.