| High-toughness cementitious composites(HTCCs)have garnered increasingly more attention due to their ability to overcome the brittle and crack-prone characteristics of traditional cement-based materials.The enhancement of HTCCs with robust wave absorption capabilities can effectively ensure the safety of special buildings in complex electromagnetic environments and broaden their application fields.In this study,we investigate the mechanism of electromagnetic wave absorption in cement-based materials and analyze the influence of various reinforced fibers and admixtures on their wave absorption performance.This is conducted at multiple scales,including electromagnetic properties,microstructure,and molecular structure.Furthermore,our study proposes a theoretical basis for enhancing the wave absorption performance of HTCCs,and synthesizes HTCCs with strong wave absorption performance.The main content of this research is as follows:·A multi-scale study is conducted to investigate the wave absorption properties,electromagnetic properties,microstructure,and molecular structure of a conventional HTCC,which shows excellent wave absorption properties.The improvement mechanism of the impedance matching property and the enhancement mechanism of the absorbing property of HTCCs are revealed.It is found that the dielectric property of cement-based materials in the microwave band is primarily influenced by the Debye relaxation process,while the magnetic property in the microwave band is predominantly controlled by the natural resonance and eddy current effect.The correlation among the microwave absorption,the electromagnetic properties,the molecular structure and the microstructures of the material is established.Specifically,the Debye relaxation process in cement-based materials is mainly influenced by molecular polarization,interfacial polarization,pore effects,and nano effects of the material.This study reveals a phenomenon that poly(vinyl alcohol)(PVA)fibers can promote calcium ion enrichment around the fibers within the matrix of cement-based materials.It also elucidates the multi-scale mechanism of the interaction between PVA fibers and fly ash,ranging from the molecular structure of hydration products to the wave absorption properties of cement-based materials.·This study investigates the effects of basalt fibers on the wave absorption properties,electromagnetic properties,and microstructure of the matrix of HTCCs.The influence of adding basalt fibers on the electromagnetic properties of cement-based materials is explored.The relationship between the microstructural changes and the influence of basalt fibers on the electromagnetic properties of cement-based materials is established.Moreover,the influence of basalt fibers on the interference waveform of the reflectivity curve of cement-based materials is analyzed.The related results can potentially contribute to the development of cement-based materials with broadband wave absorption performance.·The effects of the blending synergy of PVA fibers and basalt fibers on the wave absorption properties,electromagnetic properties,hydration products,and pore structure of HTCCs are investigated.The blending synergy of PVA fibers and basalt fibers is found to improve the impedance matching characteristics and wave absorption properties of cement-based materials.This improvement is attributed to the effect of fibers on the pore structures and the molecular structure of hydration products in HTCCs.·The effects of carbonyl iron powder as magnetic absorbers on the wave absorption properties and electromagnetic properties of cement-based materials are studied.We reveal that the carbonyl iron powder in cement-based materials exhibits a selfassembled core-shell structure.The influence of carbonyl iron powder with a selfassembled core-shell structure on the electromagnetic properties and wave absorption properties of cement-based materials is analyzed.·A HTCC with strong wave absorption performance is synthesized.The wave absorption performance of HTCCs is enhanced by optimizing the integration of analyzed reinforced fibers and mixtures and improving the impedance matching characteristics of the material based on conventional HTCCs.The developed HTCC with strong wave absorption performance exhibits excellent wave absorption properties,with an average reflectivity of-10.63 d B and effective absorption bandwidths of 14.08 GHz(<-7 d B)and 11.80 GHz(<-10 d B),respectively.Meanwhile,it has strain-hardening characteristics,thus realizing the integration of high toughness and strong wave absorption performance in cementbased materials.Our research results have advanced the knowledge and understanding of how to improve the wave absorption properties of cement-based materials.A correlation is established between the wave absorption properties,electromagnetic properties,microstructure,and molecular structure of cement-based materials at multiple scales.Our study paves the way for the multifunctionalization of HTCCs,leading to their wider range of applications. |
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