Study On The Properties Of High Iron Fly-ash And The Absorption Of Cement-based Composite Materials

With the rapid development of electronic industry, it was significance for protection against electromagnetic radiation in the civilian and military fields. There are some preconditions that can promote the use of absorbing materials in construction, such as selecting economic and effective absorbing agents without affecting the structural characteristics which get good absorption characteristics in building materials. The research on the base of high iron fly ash with iron-rich minerals characteristics, through stduy on electromagnetic properties of fly ash particles,research into the effection of high-ash cement-based material electromagnetic properties changes in the composition of materials. Through study the mechanism and influence factors, providing basic data for high iron fly ash using in cement-based absorbing materials,application of development reference of cement-based building absorbing materials, and proposing new ways of fly ash high value-added use,promoting the utilization of fly ash development.The experiments found that the iron content of fly ash particles in defferent size and density were large differences, the particle size within in the range of 45-30μm and density greater than 2.8 g/cm3 of the fly ash particles had a higher iron content, 21.5% and 52% separately. The X-diffraction analysis of fly ash showed that iron minerals were mainly hematite and magnetite, small amount of magnetic hematite, Mg-Fe spinel and Mg-Fe-Al oxide solid solution.Fly ash particles of different densities were significantly different iron minerals, there was strong diffraction peaks of the iron minerals in the larger density of fly ash particles. The magnetite was the primary minerals in fly ash particles which density larger than 2.8g/cm3. The iron mineral were differences in of different particle size of magnetic fly ash, the smaller the particle size, the stronger the diffraction peaks of iron minerals. The study with scanning electron microscopy and energy dispersive analyzer (SEM + EDS)showed, low-iron fly ash in fly ash particles were smooth and the mainly elements were Si, Al, O, etc. The iron-rich particles had the rough surface relatively,and the mainly elements were Fe, Si, Al, O, etc. The crystal could be observed on the particle surface, such as platy and quadrangular pyramid, by elemental and mineral analysis, were identified as hematite and magnetite crystals.The electromagnetic properties study of fly ash particles in different size and density show that,the dielectric of different size had some differences, but did not change significantly. The fly ash particles which density in 1.55-2.0g/cm3 had much larger dielectric than the other density of particles. Density of particles greater than 2.8 g/cm3 had some of the dielectric constant and a certain permeability. The remaining particles have a certain dielectric, but the real and imaginary parts are small. After the incorporation of high iron fly ash ,cement-based materials can improve the absorption properties of electromagnetic waves. High iron fly ash accounted for 20-40% of cement, three are some absorbtion peaks in the 2-18GHz frequency band and maximum absorption of up to 14.7dB. The thickness of cement-based material effected on the absorbing properties to a certain extent, the absorption of electromagnetic waves up to 17.7dB which thickness of 10mm, the electromagnetic wave absorption fluctuating in 7dB which thickness of 30mm. The disposal on fly ash, such as magnetic separation, grinding, high temperature and saturated lime water immersion did not improvement the microwave absorption properties of materials.The higher iron content of fly ash was not necessarily for absorbing properties of cement based materials.Structure of spherical particles of fly ash, the cenosphere content in fly ash particles, the iron mineral form in fly ash particles and the internal structure of cement-based material effected the absorbing properties of cement-based materials.The high-iron fly ash mixed with carbon fiber of 5mm and 10mm length and steel fiber of diameter 0.5mm long 10mm in cement-based materials, but the test content does not improve the absorbing properties, and about 0.1mm diameter copper fiber could significantly improve the absorbing properties of cement-based materials at higher frequencies, the absorption of more than 10dB bandwidth up to 4GHz.