Study On Cement-based Electromagnetic Shielding Composite Materials Of Ferrite, Graphite And Steel Fibers

With the rapid development of economy, electromagnetic radiation has been becomingthe fourth pollution following the atmospheric pollution, water pollution and noise pollution,which imperils the health of human beings seriously. Using cement-based electromagneticshielding composites would be one of the effective methods to protect the electromagneticradiation according to the requirement of civil buildings. Therefore it would have greatsignificance to study the cement-based electromagnetic shielding composites due to the wideapplication, facilitating construction and lower cost in civil buildings.The materials of the electromagnetic loss ability such as ferrite, graphite and steel fibershave been used in the application study of cement-based composite, this paper mainlydiscusses the electromagnetic shielding properties, electrical conductive properties, flowproperties and mechanical properties in cement-based composites with ferrite, graphite andsteel fibers, and also analyses the effects of steel fiber contents and specimens thickness onelectromagnitic shielding properties.The shielding effectiveness of cement-based compositesis measured with shielding effectiveness devices on coaxial plane fixture-spectrum analyzermethod in the frequency range of0MHz—1500MHz. Then the electrical resistivity ofspecimens is measured with four-probe method.Results show that cement mortars with steel fibers will reach the maximum shieldingeffectiveness, about12.5dB in the frequency of1500MHz and the steel fiber content is1%.After adding ferrite and steel fiber into cement mortar, the maximum of SE attaines45dB,1%of the steel fiber contents is also the percolation threshold of shielding effectiveness atthis time, and the continuous bandwidth of SE above10dB has been expanded. At the sametime, adding graphite and steel fibers, when the steel fiber content is1%, although themaximum of SE is17dB, overall electromagnetic shielding effectiveness is better than othersin the whole frequency range. When the steel fiber cotents of cemcent-based composites withferrite, graphite and steel fibers is1.5%, the maximum of SE can reach about33dB and thecontinuous bandwidth of SE above10dB is wider. For shielding effectiveness of cementmortar when its thickness is5mm and10mm, results show that the shielding effectiveness ofthe specimens is proportional to its thickness, and the effect of electromagnetic shielding isimproved in the lower frequency. When the thickness of cement mortar with graphite andsteel fibers is10mm and the steel fiber content is also1%, the maximum of SE can attainabout25dB and the continuous bandwidth of SE above10dB reaches1300MHz. Theelectromagnetic shielding bandwidth of cement-based composites with ferrite, graphite and different contents of steel fibers all reaches1200MHz, and the maximum shieldingeffectiveness of these cement-based composites are all more than30dB in the frequencyrange of800MHz—1500MHz, especially the maximum of SE can attain42dB, which showsthat these cement-based composites have very good shielding effectiveness ofelectromagnetic wave in high frequency range.Compared the electrical conductive properties of all cement mortar specimens, the betterthe electrical conductive properties of cement-based composites with the certain steel fibercontents are, the better electromagnetic shielding properties are. For exemple, the minimumelectrical resistivity of cement-based composites with graphite and steel fibers can attain0.6Ω m when the stell fiber cotent is about1%, and for the cement mortar composites with threekinds of addtives,1%of the steel fiber content is also the percolation threshold of electricalconductive properties, and the electrical resistivity reaches0.55Ω m with the best electricalconductive properties.Adding Mn-Zn ferrite, graphite and steel fibers into cement mortar specimens, theconsistency of mortar reduces about10mm-30mm than that of pure cement mortar specimens.With the additives increases, the consistency of mortar reduces, so the flow propertie isgetting worse. Therefore, the additives should be controlled in a suitable range.In general, compared to the pure cement mortar specimens, adding ferrite, graphite andsteel fibers into cement mortar can improve their flexural strength and compressive strength.But the mechanical properties of cement mortar with ferrite, graphite and steel fibers weredecreased a little compared with other cement mortars with ferrite and steel fibers or graphiteand steel fibers, then we can take some appropriate measures to improve the materialsstrength.