The Effects of Multi-Walled Carbon Nanotubes and Steel Fibers on the AC Impedance and Electromagnetic Shielding Effectiveness of High-Performance, Fiber-Reinforced Cementitious Composites

Abstract

This study aimed to investigate the effect of multi-walled carbon nanotubes (MWCNTs) and steel fibers on the AC impedance and electromagnetic shielding effectiveness (SE) of a high-performance, fiber-reinforced cementitious composite (HPFRCC). The electrical conductivity of the 100 MPa HPFRCC with 0.30% MWCNT was 0.093 S/cm and that of the 180 MPa HPFRCC with 0.4% MWCNT and 2.0% steel fiber was 0.10 S/cm. At 2.0% steel fiber and 0.3% MWCNT contents, the electromagnetic SE values of the HPFRCC were 45.8 dB (horizontal) and 42.1 dB (vertical), which are slightly higher than that (37.9 dB (horizontal)) of 2.0% steel fiber content and that (39.2 dB (horizontal)) of 0.3% MWCNT content. The incorporation of steel fibers did not result in any electrical percolation path in the HPFRCC at the micro level; therefore, a high electrical conductivity could not be achieved. At the macro level, the proper dispersion of the steel fibers into the HPFRCC helped reflect and absorb the electromagnetic waves, increasing the electromagnetic SE. The incorporation of steel fibers helped improve the electromagnetic SE regardless of the formation of percolation paths, whereas the incorporation of MWCNTs helped improve the electromagnetic SE only when percolation paths were formed in the cement matrix.

Influence of chemically treated carbon fibers on the electromagnetic shielding of ultra-high-performance fiber-reinforced concrete

“…Similarly, Hixson et al [45] reported that owing to the similar time constants between the oxide films on the steel fiber and copper electrode, the low frequency bulk arc, indicating the matrix contribution, can overlap with the electrode arc. This is also consistent with the findings of Lee et al [2] for steel-fiber-reinforced cement mortar. It is obvious that, regardless of the chemical treatment on the surface of the carbon fibers, the electrical conductivity increased with an increase in the carbon fiber content.…”

“…The shielding effectiveness of the UHPFRC was found to be 30 dB at 1.0 GHz (Fig. 11a), which was much higher than that (> 10 dB) of the plain cement mortar without steel fibers [2]. Therefore, the use of steel fibers is effective at improving the shielding effectiveness of the UHPC.…”

“…To evaluate the influence of the chemically treated carbon fibers on the electrical conductivity of UHPFRC, prismatic samples with a cross-sectional area of 60 × 60 mm 2 and a length of 160 mm were fabricated. Copper wires were used for the electrodes and wrapped around the prismatic samples in 1.5-mm deep notches that were made on the four sides using a diamond blade.…”

“…The two-probe method, which is one of the mostly commonly used methods for measuring resistivity, was adopted, and the interval of the copper wires was determined to be 30 mm. An alternative current (AC) impedance measurement was used as a previous study [2] and an LCR meter, produced by Keysight Technologies (E4980A), was used to receive the electrical signals at various frequencies (1 Hz-1 MHz).…”

“…To achieve sufficient effectiveness in the electrical conductivity and electromagnetic (EM) shielding of nonconductive concrete, which is one of the most widely used materials in building construction in the past several decades, carbon-based fibers or fillers have been adopted [1][2][3][4][5][6][7]. Electrical conductivity is required for utilizing concrete as a self-sensing material for structural health monitoring [3,8,9] and for mitigating the EM waves passing through concrete walls and its disturbance of electrical circuits and devices [1,[10][11][12][13].…”