Study On Preparation And Performance Of Cement Based Electromagnetic Shielding Mortar Composited With Graphite And Carbon Fiber

With the widely use of electronics and electrical equipments,the electromagnetic protection for structure is also increasing attention. Cement-based electromagnetic shielding mortar is a kind of material shielding electromagnetic wave for building. It has some advantages, such as simple working process, low cost and large cover area. The preparation method and electromagnetic shielding performance of mortar filled with graphite and carbon fibers were studied in this paper. This article explored the effects of various components on the physical mechanical properties and electromagnetic shielding effectiveness of cement mortar. After optimizing formula design and preparation process, mortars with excellent properties were prepared.Mortars composited with different content of graphite and carbon fiber were prepared, respectively. Research results showed that adding graphite or carbon fiber was able to reduce the resistivity of cement-based mortar, and improve the electromagnetic shielding effectiveness as well. Mortars mixed with low content of carbon fiber had lower conductivity and better electromagnetic shielding effectiveness than mortars mixed with larger dosage of graphite. When mortars mixed with both graphite and carbon fiber, they mixed with low content of carbon fiber had good electromagnetic shielding effectiveness. Shielding effectiveness of the mortar mixed with 15wt% graphite and 0.2wt% carbon fiber could reach more than 10 d B in the frequency range of 600 MHz ~1.5GHz.Cement-based mortars filled with graphite and carbon fiber were studied by means of replacing same volume of aggregates, and the influence of different kinds of aggregates on electromagnetic shielding effectiveness was analyzed. Aggregates include quartz sand, vitrified micro bubbles, and expanded polystyrene foam particles. Changing ratio of quartz sand and vitrified micro bubbles had little effect on electromagnetic shielding effectiveness. While the shielding effectiveness of mortar mixed with expanded polystyrene foam particles was improved. That maybe because it can make the surface impedance of the mortar meets the impedance of space and absorbs electromagnetic waves.Using mineral admixtures such as silica fume, fly ash and slag powders to replace the same mass of cement. Wth dosage of silica fume increasing, the electromagnetic shielding effectiveness of mortar increased gradually. But the replacement of fly ash and slag powder had little influence on the electromagnetic shielding effectiveness. Mortars composited with polymer additives were studied, mortars mixed with less than 1% mass of cement of dispersed emulsion powder had little influence on the electromagnetic shielding effectiveness, while mixed with too much powder would reduce the electromagnetic shielding effectiveness by 3 ~ 5 d B. Mixed with 0.2% cement mass fraction of sodium carboxymethyl cellulose(CMC) could reduce the electromagnetic shielding effectiveness by 2 ~ 4 d B.In addition, factors such as the water-cement ratio of mortar, the thickness of the specimen, curing age and the sample structure affecting electromagnetic shielding effectiveness of mortar were also studied this paper. With the increasing of water cement ratio or the thickness of mortar specimen, the electromagnetic shielding effectiveness of mortar increased gradually, while curing age had little effects on the shielding effectiveness of cement mortar. Mortars composited with cooper mesh or used sandwich structure could improve the shielding effectiveness of mortar. Based on the performances of specimens researched in this article, and formula of the common electromagnetic shielding mortar was optimized as cement : silica fume : slag : sand : graphite : carbon fiber(mass ratio) = 394 : 82 : 204 : 680 : 240 : 3.2. Formula of heat insulation and electromagnetic shielding mortar was optimized as cement : fly ash : silica fume : sand : expanded polystyrene particles : carbon fiber : graphite(mass ratio) = 643 : 76 : 46 : 574 : 2.1 : 3.6 : 270.