Study On High Performance Of Cement-based Composite Materials For Microwave Absorbing

With the wide application of the digital communication system and electronic equipment, electromagnetic radiation pollution become a new social pollution. In view of the current electromagnetic environment worsening and the demand of military stealth and protection, study on cement-based composite absorbing material with high efficiency, broadband and structural bearing capacity is a very important subject.The problem of cement-base composite absorbing materials is low absorption efficiency, large mass, high cost, poor stability and low bearing capacity. From three aspects of impedance matching, absorbing efficiency and structure assisted, the high performance cement-based composite absorbing materials are designed. Study the influence of admixtures, porous aggregate, absorbing agent and toughening material on wave absorbing performance, strength and resistivity. First, study the preparation method of nano Co Fe2O4 wave absorption agent. Then discuss the variety and dosage of admixture, porous aggregate, absorbing agent, fiber and other components effect on strength, resistivity and absorbing properties of high performance cement composite absorption materials.The results show that the nano–ferrite powders with the size of 50 nm were prepared by ball milling raw materials including cobalt nitrate, ferric nitrate and sodium hydroxide as well as polyvinyl alcohol as dispersant according to the stoichiometric ratio of 1:2:8.1:0.25 for about 1 hour and calcining for 3 hours at 700 ℃ in resistor furnace. The absorbing wave results show that the reflection of nano Co Fe2O4 is-8.6 d B at 16~20 GHz, when the thickness of nano ferrite Co Fe2O4 is 3 mm. The best concentration of nano ferrite is 1.0% of sodium hexametaphosphate solution by using ultrasonic dispersion technology, and the dispersion effect is best.The results of high performance cement composite absorbing material show that the cement mortar of complex containing 20% fly ash and 15% slag is higher strength, less resistivity and better absorbing effect.The glazed hollow bead mortar is higher compressive strength and less electric resistivity than expanded perlite. With double mixing of 3% graphite and 3% nano ferrite in concrete, the wave absorbing performance is better than two single mixed in concrete. The compressive strength of clay ceramsite concrete is similar to pumice concrete, but resistivity of the pumice concrete is lower than ceramsite concrete, and the absorbing performance of pumice concrete is better. In the concrete mixed with 1% steel fiber can improve the compressive strength, electrical conductivity and wave absorption performance. Above the test results, Preparation of C20 high performance of cement-based composite absorbing materials is as follows:The materials are Fly Ash,Powder: nano Ferrite, graphite, glazed hollow bead, pumice, steel fiber, water reducing agent, dispersing agent,water. The ratio of is 65:20:15:3:3:14.6:124: 12.7:1: 0.6: 50.