Synergistic effects of carbon, steel, and polypropylene fibers with ZnO on the electromagnetic shielding of rhyolitic tuff geo-tile

Abstract

Geopolymers have emerged as promising materials for incorporating supplementary additives to enhance electromagnetic (EM) shielding performance. However, the combined effects of functional powders and conductive fibers on the mechanical, electromagnetic, economic, and environmental performance of rhyolitic tuff-based geopolymers remain insufficiently understood. Therefore, this study investigated rhyolitic tuff-based geopolymers incorporating micronized calcite and ZnO at varying percentages and reinforced with 2% by volume of three distinct fiber types, namely polypropylene, brass-coated micro-steel, and carbon fibers. A comprehensive experimental program was conducted, including water absorption, shrinkage measurements, compressive and flexural strength tests, microstructural analysis, and EM shielding effectiveness measurements across the 900–6000 MHz frequency band at 100 MHz intervals. The carbon dioxide (CO₂) emissions and production costs of the developed geopolymers were also evaluated and compared with those of conventional ceramic tiles. The mechanical performance of rhyolitic tuff-based geopolymers was significantly enhanced by the incorporation of ZnO powder. However, fiber type played a pivotal role in determining the EM shielding properties. The highest total EM shielding values among the investigated fiber types were obtained for the carbon fiber-reinforced geopolymers, reaching 31.2, 42.8, 39.16, and 46.86 dB at 900, 1800, 2400, and 5000 MHz, respectively. The combination of 2.5 vol.% ZnO and 2 vol.% carbon fibers provided the highest total EM shielding performance, reaching 60.32 dB at 5800 MHz. The lowest recorded CO₂ emissions and production cost were 2.63 kg CO₂/m² and $1.30/m², respectively, corresponding to reductions of approximately 81.7% and 90.9% compared with conventional ceramic tiles. Overall, the findings demonstrate that ZnO improves the mechanical performance of rhyolitic tuff-based geopolymers, whereas carbon fibers substantially enhance their EM shielding effectiveness. The developed composites therefore offer a promising low-cost and environmentally sustainable alternative for multifunctional building applications requiring high EM shielding performance.