Development of geopolymer composites for EMI shielding from steel industry waste

In this study waste from steel industries, namely, mill scale, red dust, and iron ore fines have been used as additives in geopolymer matrix for imparting EMI shielding properties in the developed composite material. geopolymer is inherently more conductive in comparison to conventional cement matrix and helps to achieve better EMI shielding. For a 30-mm geopolymer sample the EMI SE was found to be up to 9 dB in the frequency range 0.1 to 1.5 GHz. The EMI SE values for steel industry waste material, namely, mill scale, red dust, and iron ore fine were found to be 24 dB, 12 dB, and 10 dB, respectively. The addition of iron ore fine had the least change in EMI SE value of geopolymer, while the addition of mill scale had the most change in EMI SE value of geopolymer. The addition of 10 wt% SS fiber in geopolymer control sample resulted in enhanced EMI SE value 28–69 dB. Further as little as 2 wt% of steel fiber along with mill scale helped enhance EMI SE value up to 22–67 dB. As electrical conductivity of geopolymer is low, the magnetic properties like saturation magnetization helps in improving the EMI shielding of the composites. Mill scale geopolymer had the highest saturation magnetization of 22.165 emu/g, followed by red dust geopolymer 10.69 emu/g and iron ore fine geopolymer (1.76 emu/g). The control sample had the least magnetization 1.34 emu/g and the least EMI shielding. Impedance spectroscopy and equivalent circuit modeling show that electrical conductivity alone was not responsible for the observed change in EMI SE upon addition of steel industry waste and SS fiber. The magnetic properties of the geopolymer composites were responsible for the EMI shielding in the geopolymer composites. Further, this study clearly shows that geopolymer-based EMI shielding composite material can be used as a building material due to adequate compressive strength (up to 30 MPa) of the developed material.