Design and Optimization of Double-layer Structure for Improved Electromagnetic Wave Absorbing Characteristic of Single-layer Foam Cement-based Materials Containing Carbon Black

Electromagnetic wave (EMW) absorbing properties are increasingly needed in cement-based materials; however, lightweight and broadband absorption properties are challenging to realize. This study aims to create lightweight, broadband, and highly efficient EMW-absorbing materials by investigating a foam cement-based material with single- and double-layer structures containing carbon black (CB). The results revealed that CB significantly affects the mechanical properties and electrical conductivity of foam cement-based materials. The compressive strength of the foam cement-based material containing 1.5 wt.% CB with a density of 0.9 g·cm-3 can reach 7.0 MPa and has satisfactory workability and conductivity. The dielectric properties of the foam cement-based material can be synergistically controlled by its density and CB content, and obtain favorable electric loss ability. For a single-layer structure, the optimal reflection loss (RL) value of a specimen with 10mm-thick can reach -29.67 dB with an efficient bandwidth of 0.99 GHz. In contrast, the double-layer structure exhibited remarkable broadband characteristics. When the total thickness of double-layer structure is 10 mm, the optimal two specimens can achieve a minimum RL value of -28.62 and -25.52 dB with a maximum effective bandwidth of 1.49 and 1.87 GHz, respectively. This study proposes single- and double-layer foam cement-based structures with excellent impedance matching and loss attenuation ability, and constructs an effective design method for cement-based materials to achieve lightweight and broadband absorption. In addition, these cement-based materials can be regarded as a new generation of EMW-absorbing materials in the field of construction engineering.