Reflection properties against electromagnetic waves of chopped carbon fiber reinforced cement mortar

Short carbon fiber reinforced cement mortar specimens were prepared using a "six step" molding process. The reflectivity of the specimens was measured by the NRL reflectivity test system to study the influences of carbon fiber fraction, water/cement ratio and high efficiency water reducing agents on the electromagnetic reflective properties of the mortar in the frequency bands between 8-18GHz. The results showed that the maximum absorption peak value of a non-doped carbon fiber cement mortar against the electromagnetic waves was -29.3dB. The reflection of the mortar against the electromagnetic waves were gradually increased with the increase of the carbon fiber fractions from 0.2% to 1.0%. A turning point ocurred when the carbon fiber mass fraction was 0.6%, above which all the reflectivity values were greater than -10.0dB. Under the same circumustances, the reflectivity was greater when the water/cement ratio was less than 0.6, below which the wave absorbing property of the mortar was dominant. When the water/cement ratio was over 0.6, this property remained in the high frequency bands. The reflectivity values at different frequencies were greater than -8.0dB after superplasticizers were added. Compared with the electromagnetic properties with naphthalene superplasticizers or without any superplasticizers, the mortar exhibited mainly reflection against electromagnetic waves when a polycarboxylate superplasticizer was added.