Research On Preparing And Performance For Sulphoaluminate Cement Foam Concrete Microwave Absorbing Composites

With the development of intelligent society,people are suffering from the threat of electromagnetic radiation.At present,the predicament of cement based electromagnetic wave absorbing materials of impedance mismatching,low absorbing performance and heavy self-weight which seriously limit its application.Thus the development of high efficient electromagnetic absorbing material has an important significance of national defense and society.Foam concrete used as a new kind of lightweight porous materials has many advantages like energy-saving environmental protection,convenient construction and well-behaved.The entrained air voids help the formation of homogeneous pore structure and reduce the composite dielectric constant which improves its microwave sensitivity,it has been improved its possibility of using as electromagnetic wave absorbing materials.This paper uses sulphoaluminate cement as cementing material to prepare foam concrete which possesses stable pore structure by pre-researching the HPMC as dispersing agent and polycarboxylate superplasticizer influence on its pore structure.Then this paper studies the performance of the sulphoaluminate cement foam concrete by internal doping of the nano carbon black(CB),analyzes its electromagnetic parameters by coaxial line reflection and calculates its electromagnetic wave reflectivity and absorbing properties based on the transmission line theory,the results are as follows:(1)The increased dispersing agent concentration helps to develop stable air bubbles and rise bubble surface concentration to a certain extent,however the addition of dispersing agent will affect the work performance of fresh cement paste.In fact,the growth of bubble in cement paste relate to the paste flowability,the more bubbles mix,the more influence on pore structure.(2)The mix of carbon black will increase the amount of water for normal consistency and flowability of cement paste,the flowability cannot be improved by superplasticizer with the CB content(up to 2 mass%).Considering the preparation specificity of foam concrete that it cannot be prepared with content over 2.5 wt.% CB in this case.(3)the incorporation of CB has seriously affected the mechanical strength and pore structure of foam concrete especially for the preparation of low and ultralow density foam concrete,but with the density of foam concrete increasing,instead the influence decreases,even the mechanical strength of higher density foam concrete increases due to good filling effect of nanoscale CB.(4)The introduction of foam structure greatly reduces the real part of the cement permittivity and effectively improves the dielectric loss of the cement,which advantageous to the incident electromagnetic wave transfer through the absorber rather than producing bad reflection.At the same time,the existence of high porosity will provide more space for the propagation of electromagnetic wave,which can be confined in the internal void,and then the energy can be dissipated and consumed by multiple scattering.With the incorporation of CB,the absorbing material can absorb low-frequency electromagnetic waves better.