Electromagnetic interference shielding properties of carbon fiber mortars with mill scale and red mud: A comparative study

Abstract

This study investigates the synergistic effects of incorporating carbon fiber with industrial wastes such as mill scale and red mud on the mechanical and electromagnetic properties of mortars. Carbon fiber is introduced at a volume fraction of 0.5 %, while mill scale replaces the crushed stone aggregate, and red mud replaces the cement at volume and weight ratios of 10 %, 20 %, and 30 %, respectively. The results reveal that incorporating mill scale and red mud generally reduces compressive strength. Mill scale's high density and coarse particle size can disrupt the mortar matrix, while replacing cement with red mud reduces the overall binder content, further weakening the mortar. Compared to the control sample, which does not include any conductive additives, mill scale causes approximately a 55 % reduction in compressive strength, while red mud results in about a 35 % decrease. Electromagnetic interference (EMI) shielding properties show substantial improvements with the inclusion of both mill scale and red mud in carbon fiber-reinforced mortars. Mortars containing these additives exhibit significant Shielding Effectiveness Transmission (SET) values across the 8-12 GHz frequency range, surpassing control samples that do not include admixture. Specifically, carbon fiber-reinforced mortars with 10 %, 20 %, and 30 % mill scale achieve SET values of 12-17 dB, 18-24 dB, and 25-34 dB, respectively. Similarly, mortars with 10 %, 20 %, and 30 % red mud achieve SET values of 8-11 dB, 14-27 dB, and 22-34 dB, respectively. Analysis of Shielding Absorption (SEA) values indicates that mortars with 10 %, 20 %, and 30 % mill scale and 0.5 % carbon fiber achieve SEA values of 11-15 dB, 16-23 dB, and 23-32 dB, respectively. Likewise, carbon fiber-reinforced mortars with 10 %, 20 %, and 30 % red mud achieve SEA values of 5-8 dB, 11-12 dB, and 21-31 dB, respectively. Despite the reduction in compressive strength, both additives effectively improve EMI shielding, demonstrating the feasibility of using industrial wastes for multifunctional mortar applications.