Effect of crack width on electromagnetic interference shielding effectiveness of high-performance cementitious composites containing steel and carbon fibers

In this study, the effects of carbon fibers and crack widths on the electromagnetic interference (EMI) shielding effectiveness of high-performance fiber-reinforced cementitious composites (HPFRCCs) with 2 vol.% straight steel fibers were evaluated. To this end, 0.2 vol.% carbon fibers were added and four penetrated pre-crack widths ranging from 0.02 to 0.2 mm were applied under tension. The tensile strength and electrical resistance of the composites were also investigated. The test results indicated that adding 0.2% carbon fibers effectively enhanced the tensile strength, electrical conductivity, and shielding effectiveness of the HPFRCC. Furthermore, the electrical conductivity was improved by 224%, and a 27% higher shielding effectiveness was achieved. A shielding effectiveness of 48.5 dB at 1 GHz was achieved with a specimen thickness of 25 mm. Tiny cracks with a width of 20 μm significantly reduced the EMI shielding effectiveness of the HPFRCC by approximately 40%. For the plain HPFRCC, the shielding effectiveness was not significantly affected by the crack width, as it was thoroughly cracked. The benefits of adding carbon fibers for improving the shielding effectiveness disappeared at crack widths greater than 0.1 mm. Thus, the addition of carbon fibers was effective only for HPFRCCs without cracks or with very tiny cracks of less than 40 μm.