Electromagnetic wave absorbing properties of cement-based composites bonded with a special CNTs@calcium aluminate

The dispersion of carbon nanotubes (CNTs) in the matrix of cement-based composites remains a challenge due to its poor water wettability. The cement-based composites for electromagnetic wave (EMW) absorbing were prepared with a special binder of calcium aluminate cement coated carbon nanofibers (CNTs@CAC). S71CB and S71CT, which were prepared by mixing carbon black (CB) and CNTs with CAC, respectively, were used as control experiments. The type and content of cement on EMW absorbing properties of cement-based composites were investigated by microstructure characterization as well as measurement of conductivity and electromagnetic parameters. The results showed that the cement-based composites bonded with CNTs@CAC had the best CNTs dispersion, and excellent EMW absorbing properties in the X-band compared with S71CB and S71CT, with an effective absorption bandwidth (EAB) of 3.52 GHz at a thickness of 2.4 mm. The excellent EMW absorption performance was attributed to the shell-core structure of CNTs@CAC, CNTs formed a 3D network structure in the composites during the hydration of CNTs@CAC, which contributes to enhancing the EMW loss mechanism of the cement-based composites. The CNTs network structure provided pathways for electron transport enhancing the conductive loss, and the abundant heterointerfaces enhanced the interface polarization loss of cement-based composites. Excess CNTs@CAC addition caused high conductivity, resulting in impedance mismatch that reduced the EMW absorption properties of cement-based composites. The optimum content of CNTs@CAC was 40 wt%, and the cement-based composites exhibited the best EMW absorption properties, with the EAB of 3.59 GHz obtained at a thickness of 1.9 mm.